Scanning Electron Microscopy Study of Bacterial Growth in Mycelial Extracellular Matrices

Fungi and bacteria are found living in a wide variety of environments and their interactions are important in many processes including soil health, human and animal physiology and in biotechnological applications. The specificity of interaction between these microorganisms in co-culture is difficult to establish. For example, differentiation between trivial processes as a result of stochastic mixing compared with mutualistic or antagonistic interactions. Here, we investigate a single morphological feature of co-cultures of planktonic bacterial growth within biofilm-forming liquid cultures of mycelium. Namely, the attachment of bacterial co-habitants of species Bacillus subtilis to fungal hyphae of species Hericium erinaceus . The bacteria-in-mycelial-biofilm method was developed and utilised to allow for attachment of bacteria to hyphae via containment within extracellular polymeric substances (EPS) and the overall extracellular matrix (ECM) of the mycelium. Attachment structures appear to result from the hyphal surface as a result of production of EPS. The mean biofilm area across T1-3 was 3.90 ( µ m ² ) ± 0.72 ( µ m ² ) and the mean percentage coverage was 18.33 (%) ± 5.52 (%). The bacterial biofilm components could not be ruled out as co-contributing to formation of attachment structures due to the structures being present connecting individual bacterium as well as to hyphae.