Emergent particle collection by cyanobacteria through gliding motility and filament buckling

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1. 

   eLife

   Sep 17, 2026

   eLife Assessment

   This manuscript presents important work on macrostructure formation in a freshwater filamentous cyanobacterium, focusing on its ability to aggregate and buckle. The authors employ a wide range of experiments and approaches, including time-lapse imaging and 3D theoretical modelling, to establish the physical dynamics of filaments, such as gliding motility and buckling. They demonstrate that, in addition to gliding motility, filament length and flexibility are essential for the ability of cyanobacteria to capture particles and form aggregates. Overall, the study provides convincing evidence and advances our understanding of the role of microbial motility in the environment. It will be of broad interest to biophysicists and environmental microbiologists.

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2. 

   eLife

   Sep 17, 2026

   Reviewer #1 (Public review):

   Summary:

   In this manuscript, the authors investigate the mechanisms underlying macrostructure formation in a freshwater filamentous cyanobacterium strain, F. draycotensis, focusing on how its ability to aggregate and form these structures depends on the physical properties of the filaments. Using experimental observations, they demonstrate that the cyanobacterium actively captures and surrounds particles, a process driven primarily by gliding motility.

   To explain these physical dynamics, the authors present a 3D model indicating that particle collection relies on filament length, as well as a specific mechanical response, namely, filament buckling and the subsequent formation of loops of bundles of filaments. While the authors have previously documented the buckling and looping characteristics of this …

   Reviewer #1 (Public review):

   Summary:

   In this manuscript, the authors investigate the mechanisms underlying macrostructure formation in a freshwater filamentous cyanobacterium strain, F. draycotensis, focusing on how its ability to aggregate and form these structures depends on the physical properties of the filaments. Using experimental observations, they demonstrate that the cyanobacterium actively captures and surrounds particles, a process driven primarily by gliding motility.

   To explain these physical dynamics, the authors present a 3D model indicating that particle collection relies on filament length, as well as a specific mechanical response, namely, filament buckling and the subsequent formation of loops of bundles of filaments. While the authors have previously documented the buckling and looping characteristics of this strain, this study provides new insight by demonstrating that these physical phenomena are essential for particle capture and collection.

   Strengths:

   This manuscript benefits from a rigorous and detailed quantitative analysis of video recordings, which clearly documents the motility, buckling behaviour, and particle collection dynamics of the filaments.

   The authors effectively validate their hypothesis by using a naturally shorter filamentous strain, which fails to collect particles, suggesting that filament length is indeed a critical parameter.

   To further confirm the length dependency within the same species, the authors experimentally generated shorter filaments of F. draycotensis. The fact that these shortened filaments also lose the capacity to collect particles provides strong evidence supporting their proposed mechanism.

   Weaknesses:

   There is a conceptual concern. The authors linked the specific physical properties of this strain to evolutionary data, highlighting that the studied lineages diverged approximately two billion years ago. This creates a misleading impression that particle collection via flexible looping filaments is a recent evolutionary adaptation. However, particle collection has been observed in other cyanobacteria, such as Trichodesmium, which features short, rigid filaments. Therefore, the term "emerging" does not seem appropriate for the title and text. The capacity to collect particles in the studied strain F. draycotensis appears to be primarily a function of physical characteristics (filament length and flexibility) rather than evolutionary age. Any cyanobacterial strain possessing similar physical properties is likely to exhibit comparable behaviour, rendering the evolutionary timeframe largely irrelevant to the core mechanism. In addition, the phylogenetic tree presented in Figure S5 does not reflect the current consensus on cyanobacterial evolution and systematics and does not align with modern phylogenomic frameworks (see, for example, Strunecky et al., 2023 https://doi.org/10.1111/jpy.13304). There is also no such order Cyanobacteriales, which has been mentioned in a few older publications but is clearly outdated.

   Another concern is that the authors nearly completely ignore the role of type IV pili in the gliding motility of cyanobacteria, including filamentous strains. For a long time, there was a misconception that the gliding motility of cyanobacteria was due to slime protrusion. Slime plays a role in this process. However, several studies have shown that filamentous strains also use type IV pili to glide on surfaces. The authors should discuss this and include it in their model. In addition, the authors concluded that gliding motility is responsible for particle collection by Fluctiforma draycotensis. Although I believe that their conclusion is correct, there might be several limitations to the experiments which allow for other reasons to be considered. Their conclusions were based on the use of a non-motile strain and an unspecified community without the motile Fluctiforma draycotensis strain. The problem I see here is that it is not clear why this strain is not motile; it could be because of the lack of type IV pili, mutations which alter their functionality, defects in slime secretion, any other mutation (e.g. in chemoreceptors), cellular structure, metabolism, or combinations of these. Furthermore, it is possible that the community changes its composition and behaviour when it lives without the cyanobacterium with a rich carbon source (glucose) or with a non-motile cyanobacterium which may not secrete slime or, for example, a signalling component which controls behaviour of the bacteria in the community. For that reason, the authors should be more cautious with their conclusion that solely motility behaviour of Fluctiforma draycotensis is responsible for particle collection. Additional factors might be responsible for these effects.

   Read the original source
3. 

   eLife

   Sep 17, 2026

   Reviewer #2 (Public review):

   Summary:

   The authors studied aggregation, buckling, and particle collection by the filamentous cyanobacterium Fluctiforma draycotensis, as well as by the filamentous Pseudanabaena sp. (order Pseudoanabenales). They performed a range of experiments, from imaging individual gliding filaments to multiple-day experiments showing the formation of large aggregates around a particle formed from a precipitate. They also developed a model of buckling filaments to argue that the ability of elastic filaments to collect particles and form macrostructures is confined to a part of the filament phase space in terms of length and flexibility, meaning that gliding combined with certain filament length and flexibility naturally reproduces the observations.

   Strengths:

   This is an impressive study that uses multiple tools to …

   Reviewer #2 (Public review):

   Summary:

   The authors studied aggregation, buckling, and particle collection by the filamentous cyanobacterium Fluctiforma draycotensis, as well as by the filamentous Pseudanabaena sp. (order Pseudoanabenales). They performed a range of experiments, from imaging individual gliding filaments to multiple-day experiments showing the formation of large aggregates around a particle formed from a precipitate. They also developed a model of buckling filaments to argue that the ability of elastic filaments to collect particles and form macrostructures is confined to a part of the filament phase space in terms of length and flexibility, meaning that gliding combined with certain filament length and flexibility naturally reproduces the observations.

   Strengths:

   This is an impressive study that uses multiple tools to connect macrostructure formation with filaments' gliding motility and buckling. It adds an important perspective on the biological and physical factors at play in the emergence of aggregates.

   Weaknesses:

   The authors ignore the possibility that filament behavior plays an important role in the emergence of the observed patterns. Cyanobacteria have been shown to control their gliding motility (Pfreundt et al Science 2023; Kurjahn et al Nature Comm 2024), and their molecular motors are known to be regulated by chemotaxis-like signaling pathways (Risser ARM 2025). As far as I know, how the coordination between the pulling agents along an individual filament works is actively debated, but there seems to be little doubt that it exists.

   To illustrate this point better, note that the aggregation observed by the authors is consistent with the length-dependent ability of filaments to coordinate gliding (I'm not saying this is how it works in Fluctiforma draycotensis; I'm saying it's consistent). Suppose the coordination requires sufficiently long filaments, which could be the case when signaling molecules travel along the filament, propagating information about when individual pulling agents should reverse. In such a model, short filaments act randomly because they fail to coordinate gliding by the time they glide off nascent aggregates, whereas longer filaments can perform informed reversals because they have more time for coordination. Such behavior then explains the lack of aggregation in Pseudanabaena sp. (via behavior, not lack of stiffness). Note that Trichodesmium is stiff; its filaments do not buckle, yet Trichodesmium forms organized aggregates via tightly controlled motility. Note also that, as the authors report, since Pseudanabaena sp. is both shorter and faster, its filaments have relatively (to the time needed to glide the filaments' length) little time to coordinate reversals. In my opinion, whether the observed patterns passively emerge from gliding and buckling or result from active behavior remains an open question.

   I also have a small suggestion regarding this statement on model novelty:

   The essential novelty of this model is that the filament itself is active and out of equilibrium, and additionally, the forces and torques are applied locally along its centreline, and not at its extremities as in previous steady-state mechanical studies of elastic, twistable filaments such as DNA [31-33] (see Methods and SI).

   This statement needs to be revised as it ignores a substantial body of work on self-organization of active filaments: (R. E. Isele-Holder, J. Elgeti, G. Gompper, Soft Matter 2015; Pfreudnt et al, Science 2023; Faluweki et al PRL 2023; Kurjahn et al Nature Comm 2024).

   Last point: the authors often say that their observations are reproducible ('...reproducibly forms macroscopic granules...'). What is meant? Different experiments on different days, different aliquots?

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4. 

   eLife

   Sep 17, 2026

   Reviewer #3 (Public review):

   Summary:

   The authors report and characterize the formation of aggregate microstructures by the motile filamentous cyanobacterium Fluctiforma draycotensis, which exhibits gliding motility accompanied by rotation along the long axis while excreting EPS. In experiments with motile F. draycotensis cultures, they observed the formation of granular structures composed of cyanobacteria and other material (iron, polystyrene beads, etc.), with macrostructures on the scale of 1mm within 24 hours. The structures were motile at speeds comparable to that of the cyanobacteria filaments, resulting in their growth through coalescence over time. Notably, such macrostructures were absent in nonmotile F. draycotensis, pointing to the role of filament motility in their formation. Through experiments examining the micro-scale …

   Reviewer #3 (Public review):

   Summary:

   The authors report and characterize the formation of aggregate microstructures by the motile filamentous cyanobacterium Fluctiforma draycotensis, which exhibits gliding motility accompanied by rotation along the long axis while excreting EPS. In experiments with motile F. draycotensis cultures, they observed the formation of granular structures composed of cyanobacteria and other material (iron, polystyrene beads, etc.), with macrostructures on the scale of 1mm within 24 hours. The structures were motile at speeds comparable to that of the cyanobacteria filaments, resulting in their growth through coalescence over time. Notably, such macrostructures were absent in nonmotile F. draycotensis, pointing to the role of filament motility in their formation. Through experiments examining the micro-scale dynamics, inert material such as small polystyrene beads was found to be transported by the gliding, buckling, and plectoneme dynamics of the filaments, pointing to the underlying mechanism by which particles are collected into larger-scale microgranule structures.

   To interrogate the properties that drive the cyanobacteria filament buckling, plectoneme formation, and entanglement, the authors develop a mechanical model for filaments as nearly inextensible, slender bodies with resistance to twisting and bending under active gliding forces and torques and responding to fluid flows and surface adhesion. They derive expressions for the thresholds for buckling and twisting instabilities, which are additionally demonstrated and interrogated through simulation via the Immersed Boundary Method. Most importantly, bending and plectoneme formation only occur with sufficiently long filaments, and the threshold is shorter for bending than for plectoneme formation. Experimental observations with wild-type filaments agree with the model-predicted thresholds. The authors perform additional experiments with shorter filaments below both thresholds, including the filamentous bacterium Pseudanabaena, which fail to collect particles (though can in principle form macrostructures).

   Strengths:

   This work appears to be novel (notably, the discovery and characterization of the particle collection behavior of a filamentous cyanobacterium) and has interesting implications for both naturally observed cyanobacterial macrostructures as well as the controllable parameters in engineering them. The experimental and modeling work is well motivated, contributing to the broader understanding of macrostructure formation and material aggregation through active filament dynamics (not exclusive to cyanobacteria), as well as the underlying physical properties governing important filamentous cyanobacterium dynamics. As such, I would expect the results of this paper to be of broad interest to both biophysicists and microbiologists. Generally, the manuscript is well written with clear, compelling figures that illustrate the important conclusions of this study.

   Weaknesses:

   In the section on "Shorter gliding filaments cannot collect particles nor form granule macrostructures", the filamentous cyanobacteria considered *all* fall below the predicted thresholds for bending and twisting. The "long" F. draycotensis are 60 microns in length, notably less than the 120 and 320 micron thresholds derived in the previous section as well as the lengths of filaments considered in Figure 3D, yet these "long" 60 micron filaments form macrostructures. How can this be understood in the context of the model predictions? Is the nature of the macrostructures in Figure 4B, the microscale parameters, or the collection of particles somehow different than those with filaments an order of magnitude longer in earlier parts of the paper? The paper would be stronger if these sorts of questions were addressed in the text and/or with supplementary figures.

   Read the original source
5. 

   eLife

   Sep 17, 2026

   Author response:

   Public Reviews:

   Reviewer #1 (Public review):

   Summary.

   In this manuscript, the authors investigate the mechanisms underlying macrostructure formation in a freshwater filamentous cyanobacterium strain, F. draycotensis, focusing on how its ability to aggregate and form these structures depends on the physical properties of the filaments. Using experimental observations, they demonstrate that the cyanobacterium actively captures and surrounds particles, a process driven primarily by gliding motility.

   To explain these physical dynamics, the authors present a 3D model indicating that particle collection relies on filament length, as well as a specific mechanical response, namely, filament buckling and the subsequent formation of loops of bundles of filaments. While the authors have previously documented the buckling and …

   Author response:

   Public Reviews:

   Reviewer #1 (Public review):

   Summary.

   In this manuscript, the authors investigate the mechanisms underlying macrostructure formation in a freshwater filamentous cyanobacterium strain, F. draycotensis, focusing on how its ability to aggregate and form these structures depends on the physical properties of the filaments. Using experimental observations, they demonstrate that the cyanobacterium actively captures and surrounds particles, a process driven primarily by gliding motility.

   To explain these physical dynamics, the authors present a 3D model indicating that particle collection relies on filament length, as well as a specific mechanical response, namely, filament buckling and the subsequent formation of loops of bundles of filaments. While the authors have previously documented the buckling and looping characteristics of this strain, this study provides new insight by demonstrating that these physical phenomena are essential for particle capture and collection.

   Strengths:

   This manuscript benefits from a rigorous and detailed quantitative analysis of video recordings, which clearly documents the motility, buckling behaviour, and particle collection dynamics of the filaments.

   The authors effectively validate their hypothesis by using a naturally shorter filamentous strain, which fails to collect particles, suggesting that filament length is indeed a critical parameter.

   To further confirm the length dependency within the same species, the authors experimentally generated shorter filaments of F. draycotensis. The fact that these shortened filaments also lose the capacity to collect particles provides strong evidence supporting their proposed mechanism.

   We thank the reviewer for the accurate summary of our work and for their identified strengths of the study.

   Weaknesses:

   There is a conceptual concern. The authors linked the specific physical properties of this strain to evolutionary data, highlighting that the studied lineages diverged approximately two billion years ago. This creates a misleading impression that particle collection via flexible looping filaments is a recent evolutionary adaptation. However, particle collection has been observed in other cyanobacteria, such as Trichodesmium, which features short, rigid filaments. Therefore, the term ”emerging” does not seem appropriate for the title and text. The capacity to collect particles in the studied strain F. draycotensis appears to be primarily a function of physical characteristics (filament length and flexibility) rather than evolutionary age. Any cyanobacterial strain possessing similar physical properties is likely to exhibit comparable behaviour, rendering the evolutionary timeframe largely irrelevant to the core mechanism.

   We would like to first clarify our use of the term “emergent”. It seems that the referee took this in an evolutionary context, whereas we are using this term in the context of its use in systems dynamics, and referring to: “a complex entity displaying behaviors that its components do not have on their own, and emerge only when they interact in a wider whole”. Here, particle collection and dynamic aggregate formation “emerges” from the buckling and interaction of many filaments.

   With regards to the evolution of particle collection behavior, our comment on the evolutionary distance between F. draycotensis and Pseudoanabena sp. was meant to highlight the point that particle collection seems to be a function of physical characteristics and motility: Despite a large evolutionary distance, and possibly many biological differences, a physics-based argument is capturing the difference between the particle collection ability of these two organisms. Thus, we are in agreement here with the reviewer. We did not intend to make any arguments about “evolutionary age” of the particle collection behavior.

   We see that the short, evolutionary comment in the Introduction has confused the reviewer and potentially is confusing to other readers too. We will therefore remove this evolutionary comment from the Introduction section of the revised manuscript and make the point in more detail in the Discussion section.

   In addition, the phylogenetic tree presented in Figure S5 does not reflect the current consensus on cyanobacterial evolution and systematics and does not align with modern phylogenomic frameworks (see, for example, Strunecky et al., 2023 https://doi.org/10.1111/jpy.13304). There is also no such order Cyanobacteriales, which has been mentioned in a few older publications but is clearly outdated.

   We thank the reviewer for this comment, as it has made us realise that we never explained our choice of taxonomic framework in the manuscript, and perhaps this is the source of the confusion.

   The order Cyanobacteriales does exist: it is the order-level name applied in the Genome Taxonomy Database (GTDB) [5, 6], currently the most comprehensive and actively curated genome-based taxonomy of prokaryotes. GTDB classifies taxonomic groups algorithmically, as monophyletic groups in a concatenated marker-protein phylogeny with ranks normalised by relative evolutionary divergence. This has produced a number of re-groupings and new names relative to the older, morphology-derived classifications; many of these have since been formally proposed under the International Code of Nomenclature of Prokaryotes and the SeqCode [2], and are progressively being adopted by the NCBI. The placement of Cyanobacteriales, and of the other orders shown in Figure S5, can be inspected directly on the GTDB “Taxonomy Tree” (see here for the orders within the class Cyanobacteriia).

   We would also like to note that we do not see our tree and the framework of Strunecky et al. as being in conflict. Strunecky et al. constructed their phylogenomic backbone using GTDB-Tk and the same 120-marker concatenated alignment that the GTDB itself uses. What differs between the two schemes is therefore not the underlying phylogeny but the nomenclature applied to the resulting clades: Strunecky et al. work within the botanical tradition and combine the phylogenomic tree with phenotypic characteristics, thereby proposing ten new orders and fifteen new families, whereas GTDB assigns rank boundaries purely by evolutionary divergence and so draws broader order limits. In practice, the GTDB order Cyanobacteriales spans several of the families (e.g. Oscillatoriales and Coleofasciculales) and orders (e.g. Chroococcales and Nostocales), that are proposed within the Strunecky et al. work. Our reason for adopting the GTDB nomenclature is for practical reasons specific to this study. F. draycotensis is a recently described organism [3] that is not included in Strunecky et al. and has no placement in their tree. In GTDB it falls within a family-level lineage (placeholder name JAAUUE01) inside the Cyanobacteriales, with the sequenced members of the Coleofasciculaceae as its closest relatives. We could not have assigned it to one of the Strunecky orders without inventing a placement. The same applies to some of the other, recent metagenomically described cyanobacteria [10], which similarly have no assigned names in the literature. GTDB, by contrast, provides a reproducible, algorithmic assignment for all of these genomes, and is now widely used for this reason in genome- and metagenome-based studies of cyanobacteria (e.g. [1]). We therefore used it consistently throughout.

   Finally, with regards to the reviewer’s point about the tree itself, we would like to note that Figure S5 was intended only to convey the evolutionary distance between F. draycotensis and Pseudanabaena sp., and it was built from a modest set of six concatenated ribosomal protein markers using an approximate maximum-likelihood method with SH-like local support values. This is considerably less rigorous than the 120-marker RAxML and Bayesian analysis of Strunecky et al., and we agree that a stronger tree may be preferable. For the revised manuscript we are recomputing the tree from a substantially larger set of concatenated single-copy marker genes, using IQTREE with model selection and non-parametric bootstrap support. We would note, however, that the specific conclusion drawn from this figure — that the two strains we use for our experimental work, namely F. draycotensis and Pseudoanabena sp. belong to deeply divergent cyanobacterial lineages — is supported by the deep backbone of the cyanobacterial tree, which is stable across marker sets and inference methods, and is equally supported by the tree of Strunecky et al.

   We will make these points clearer in the Methods and Discussion sections of the revised manuscript, as well as the Figure S5 legend.

   Another concern is that the authors nearly completely ignore the role of type IV pili in the gliding motility of cyanobacteria, including filamentous strains. For a long time, there was a misconception that the gliding motility of cyanobacteria was due to slime protrusion. Slime plays a role in this process. However, several studies have shown that filamentous strains also use type IV pili to glide on surfaces. The authors should discuss this and include it in their model.

   The reviewer is correct that we did not include molecular details of gliding motility in our biophysical model. They are also correct to point out that pili and slime biosynthesis genes are shown to be involved in gliding motility [8]. It is, however, still unclear how these factors interact to produce mechanical gliding forces that can result in filament rotation (observed only in some filamentous cyanobacteria), filament reversal, as well as decoordination during such reversals, which we have previously shown in F. draycotensis [9]. Therefore, we have chosen to keep the biophysical model at a coarse-grained, phenomenological level. Instead of explicitly modelling the detailed molecular mechanisms behind force generation, we model only the minimum necessary physical forces and torques needed to reproduce the observed rotation and translation of the filament during gliding under de-coordinated conditions. This model is able to reproduce the experimentally observed buckling and twisting of filaments, and is therefore sufficient and useful to achieve a coarse-grained understanding of mechanical forces and their relationship to buckling, twisting and entanglement, which are the main processes we focus on here. As molecular details behind force generation in rotating, filamentous cyanobacteria become available, more detailed physical models can be constructed. We also note, in this context, that the two filamentous cyanobacteria we compare both encode the type IV pilus machinery, so the presence of a pilus motor does not by itself distinguish a particle-collecting from a non-collecting strain (see our response to the reviewer’s next point).

   We will make these points clearer in the Methods and Discussion sections of the revised manuscript.

   In addition, the authors concluded that gliding motility is responsible for particle collection by Fluctiforma draycotensis. Although I believe that their conclusion is correct, there might be several limitations to the experiments which allow for other reasons to be considered. Their conclusions were based on the use of a non-motile strain and an unspecified community without the motile Fluctiforma draycotensis strain. The problem I see here is that it is not clear why this strain is not motile; it could be because of the lack of type IV pili, mutations which alter their functionality, defects in slime secretion, any other mutation (e.g. in chemoreceptors), cellular structure, metabolism, or combinations of these. Furthermore, it is possible that the community changes its composition and behaviour when it lives without the cyanobacterium with a rich carbon source (glucose) or with a non-motile cyanobacterium which may not secrete slime or, for example, a signalling component which controls behaviour of the bacteria in the community. For that reason, the authors should be more cautious with their conclusion that solely motility behaviour of Fluctiforma draycotensis is responsible for particle collection. Additional factors might be responsible for these effects.

   Our conclusion that gliding motility is the main factor underpinning particle collection is based on several observations.

   Firstly, on the macroscopic scale we present several control experiments where we did not observe particle collection: (i) in the community featuring a non-motile F. draycotensis, and with mostly the same other bacterial species as the community featuring the motile F. draycotensis, (ii) in a bacterial community derived from the original F. draycotensis community but lacking any cyanobacteria, (iii) in the original community with physically shortened F. draycotensis, and (iv) in another cyanobacterial community featuring different bacteria and a naturally shorter, filamentous gliding cyanobacteria Pseudanabaena sp. A straightforward, parsimonious explanation that satisfies all these observations is that particle collection is underpinned by physical characteristics of gliding filamentous cyanobacteria.

   Secondly and more directly, in time-lapse microscopy imaging we repeatedly observe clusters of beads being moved by gliding filaments, and thereby being collected into larger clusters. Thus, whilst factors such as slime secretion also contribute, the primary mechanism driving the observed particle motion seems to be that particles stick to filaments and are carried around with them as they glide. We cannot rule out a contribution of pili to bead attachment and transport. We note, however, that both cyanobacteria compared here encode the type IV pilus machinery. In a homology survey of the two genomes, Pseudanabaena sp. and F. draycotensis both carry orthologues of the core T4P components — the assembly ATPase PilB, the retraction ATPase PilT, the inner-membrane platform protein PilC, the prepilin peptidase PilD, and the alignment-complex proteins PilM and PilF — together with the hormogonium-associated hmpD, hmpF and hmpG. Pseudanabaena sp. is therefore not pilus-deficient, and it does glide, yet it does not collect particles. The difference between the two organisms consequently cannot be attributed to the presence or absence of the pilus motor, which we would argue supports the physical argument we make here. Consistent with this, we have not identified mutations in pilus-related genes in the mutant, non-motile F. draycotensis.

   We are currently in the process of preparing another manuscript describing the mutations that led to motility loss in the non-motile F. draycotensis, as well as the proteins that are differentially expressed in the motile and non-motile F. draycotensis. These analyses will shed more light on the molecular mechanisms abolishing motility and how they might be influencing particle collection.

   In the revised manuscript, we will make these points clearer in the Discussion section.

   Reviewer #2 (Public review):

   Summary:

   The authors studied aggregation, buckling, and particle collection by the filamentous cyanobacterium Fluctiforma draycotensis, as well as by the filamentous Pseudanabaena sp. (order Pseudoanabenales). They performed a range of experiments, from imaging individual gliding filaments to multiple-day experiments showing the formation of large aggregates around a particle formed from a precipitate. They also developed a model of buckling filaments to argue that the ability of elastic filaments to collect particles and form macrostructures is confined to a part of the filament phase space in terms of length and flexibility, meaning that gliding combined with certain filament length and flexibility naturally reproduces the observations.

   Strengths:

   This is an impressive study that uses multiple tools to connect macrostructure formation with filaments’ gliding motility and buckling. It adds an important perspective on the biological and physical factors at play in the emergence of aggregates.

   We thank the reviewer for the accurate summary of our work and highlighting the strengths of the study.

   Weaknesses:

   The authors ignore the possibility that filament behavior plays an important role in the emergence of the observed patterns. Cyanobacteria have been shown to control their gliding motility (Pfreundt et al Science 2023; Kurjahn et al Nature Comm 2024), and their molecular motors are known to be regulated by chemotaxislike signaling pathways (Risser ARM 2025). As far as I know, how the coordination between the pulling agents along an individual filament works is actively debated, but there seems to be little doubt that it exists.

   To illustrate this point better, note that the aggregation observed by the authors is consistent with the length-dependent ability of filaments to coordinate gliding (I’m not saying this is how it works in Fluctiforma draycotensis; I’m saying it’s consistent). Suppose the coordination requires sufficiently long filaments, which could be the case when signaling molecules travel along the filament, propagating information about when individual pulling agents should reverse. In such a model, short filaments act randomly because they fail to coordinate gliding by the time they glide off nascent aggregates, whereas longer filaments can perform informed reversals because they have more time for coordination. Such behavior then explains the lack of aggregation in Pseudanabaena sp. (via behavior, not lack of stiffness). Note that Trichodesmium is stiff; its filaments do not buckle, yet Trichodesmium forms organized aggregates via tightly controlled motility. Note also that, as the authors report, since Pseudanabaena sp. is both shorter and faster, its filaments have relatively (to the time needed to glide the filaments’ length) little time to coordinate reversals. In my opinion, whether the observed patterns passively emerge from gliding and buckling or result from active behavior remains an open question.

   We appreciate the comment by the reviewer. We certainly agree that behavioral responses exist in filamentous cyanobacteria and will interplay with the physical aspects to produce exciting, complex dynamics. Besides the exemplar ideas that the reviewer provides, there can be many other scenarios involving behavioral responses, such as responses to light and to quorum sensing molecules or photosynthesis-generated radicals. For example, in F. draycotensis we have observed photo-responses at the aggregate level, which we are are currently studying. Photoresponses are also observed in Trichodesmium aggregates [7]. In general, a full understanding of the interaction of the biological (i.e. behavioral) and the physical aspects will require several future studies.

   In the current study, however, we focus on characterising the physical aspects of gliding motility alone, combined with experimental observations. We believe that this approach is important to establish a form of “null expectation” from the physics of gliding, elastic filaments alone. Currently, the molecular mechanisms responsible for coordinating the reversal behaviour of multiple filaments are still unclear, so it is difficult to experimentally demonstrate behavioural contributions to aggregate formation, e.g. via experiments where such behaviour is switched off. In the meantime, simulations such as those presented here allow us to test more precisely the potential role of activity, coordinated reversals and the elastic properties of the filament. In future it will be interesting to scale up the presented model to include multiple interacting filaments, and to systematically test the respective roles of active coordination behaviour for one individual filament (reversals) and for multiple interacting filaments (where contacts modulate activity), as well as the physical properties (length and flexibility). Such modelling studies can then identify if a ‘purely physical’ model can or cannot generate realistic aggregates, and pinpoint whether additional coordination mechanisms are needed to regulate aggregation. By testing the combination of different physical and biological coordination mechanisms, it would then help to indicate how much of a role is played by various potential active coordination behaviours.

   We will bring out this point more clearly in the Discussion section of the revised manuscript.

   I also have a small suggestion regarding this statement on model novelty:

   The essential novelty of this model is that the filament itself is active and out of equilibrium, and additionally, the forces and torques are applied locally along its centreline, and not at its extremities as in previous steady-state mechanical studies of elastic, twistable filaments such as DNA [31-33] (see Methods and SI).

   This statement needs to be revised as it ignores a substantial body of work on self-organization of active filaments: (R. E. Isele-Holder, J. Elgeti, G. Gompper, Soft Matter 2015; Pfreudnt et al, Science 2023; Faluweki et al PRL 2023; Kurjahn et al Nature Comm 2024).

   We agree with the reviewer that there is a significant literature on active filaments, some of which we have already cited and will now discuss in more details, as well as adding and discussing the suggested additional references. Our statement on “model novelty” refers to the analysis of buckling instabilities of biological filaments, and in particular DNA, due to a combination of forces and torques. To our knowledge, this has only be studied explicitely by [4], and only in the local (resistive force theory) limit. The elastohydrodynamic simulations coupled to local active forces and torques, as we implemented here, are therefore novel and will expand the analysis of both microbial filaments and other biological polymers. We will clarify these points in the Methods and Discussion sections of the revised manuscript.

   Last point: the authors often say that their observations are reproducible (’...reproducibly forms macroscopic granules...’). What is meant? Different experiments on different days, different aliquots?

   The “replicability” statement was in reference to different experiments started on different days using cultures obtained from serial transfer experiments, as well as cultures re-initiated from cyrostocks. This point will be made clear in the revised manuscript.

   Reviewer #3 (Public review):

   Summary:

   The authors report and characterize the formation of aggregate microstructures by the motile filamentous cyanobacterium Fluctiforma draycotensis, which exhibits gliding motility accompanied by rotation along the long axis while excreting EPS. In experiments with motile F. draycotensis cultures, they observed the formation of granular structures composed of cyanobacteria and other material (iron, polystyrene beads, etc.), with macrostructures on the scale of 1mm within 24 hours. The structures were motile at speeds comparable to that of the cyanobacteria filaments, resulting in their growth through coalescence over time. Notably, such macrostructures were absent in nonmotile F. draycotensis, pointing to the role of filament motility in their formation. Through experiments examining the micro-scale dynamics, inert material such as small polystyrene beads was found to be transported by the gliding, buckling, and plectoneme dynamics of the filaments, pointing to the underlying mechanism by which particles are collected into larger-scale microgranule structures.

   To interrogate the properties that drive the cyanobacteria filament buckling, plectoneme formation, and entanglement, the authors develop a mechanical model for filaments as nearly inextensible, slender bodies with resistance to twisting and bending under active gliding forces and torques and responding to fluid flows and surface adhesion. They derive expressions for the thresholds for buckling and twisting instabilities, which are additionally demonstrated and interrogated through simulation via the Immersed Boundary Method. Most importantly, bending and plectoneme formation only occur with sufficiently long filaments, and the threshold is shorter for bending than for plectoneme formation. Experimental observations with wild-type filaments agree with the model-predicted thresholds. The authors perform additional experiments with shorter filaments below both thresholds, including the filamentous bacterium Pseudanabaena, which fail to collect particles (though can in principle form macrostructures).

   Strengths:

   This work appears to be novel (notably, the discovery and characterization of the particle collection behavior of a filamentous cyanobacterium) and has interesting implications for both naturally observed cyanobacterial macrostructures as well as the controllable parameters in engineering them. The experimental and modeling work is well motivated, contributing to the broader understanding of macrostructure formation and material aggregation through active filament dynamics (not exclusive to cyanobacteria), as well as the underlying physical properties governing important filamentous cyanobacterium dynamics. As such, I would expect the results of this paper to be of broad interest to both biophysicists and microbiologists. Generally, the manuscript is well written with clear, compelling figures that illustrate the important conclusions of this study.

   We thank the reviewer for the accurate summary of our work and recognising the broad relevance of the study.

   Weaknesses:

   In the section on “Shorter gliding filaments cannot collect particles nor form granule macrostructures”, the filamentous cyanobacteria considered “all” fall below the predicted thresholds for bending and twisting. The “long” F. draycotensis are 60 microns in length, notably less than the 120 and 320 micron thresholds derived in the previous section as well as the lengths of filaments considered in Figure 3D, yet these “long” 60 micron filaments form macrostructures. How can this be understood in the context of the model predictions? Is the nature of the macrostructures in Figure 4B, the microscale parameters, or the collection of particles somehow different than those with filaments an order of magnitude longer in earlier parts of the paper? The paper would be stronger if these sorts of questions were addressed in the text and/or with supplementary figures.

   We thank the reviewer for this point. Indeed as we mention in the text, the ‘long’ population has a mean length of 60 micron. However, as shown in the length distribution plot in Fig 4A, the maximum filament lengths observed in these populations (within the samples used for microscopy) are 560 microns for the long filaments, versus 240 microns for the short filaments. Thus, we expect the long population to contain multiple filaments that can buckle and a few that can form plectonemes, whilst the short population might have some buckling filaments and none that form plectonemes. We stress that Fig 4A only shows the length distribution for what we believe to be a representative sample taken from the long and short populations, not the full data from the entire population.

   We will revise the main text to include the maximum filament lengths of the two populations as well as the mean values. We will also add lines to Fig 4A to indicate the buckling and plectoneme threshold lengths from the analytical estimate for the F. draycotensis filaments (same values as in Fig 3), to make it clear that the long population contains more buckling/plectoneming filaments than the short population.

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   Version published to 10.64898/2026.04.28.721293 on bioRxiv

   Apr 29, 2026