Exploration and characterization of a newly isolated bacterium, Enterobacter quasihormaechei strain BDIFST24001, capable of producing rhamnolipid biosurfactant for oil remediation

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Abstract

Biosurfactants are naturally occurring compounds synthesized by micro-organisms that increasingly attract attention due to both their living area and application in various industries. In this study, we explore and characterize a novel bacterium, Enterobacter quasihormaechei strain BDIFST24001, isolated for its ability to produce rhamnolipid biosurfactants, with the aim of facilitating oil remediation processes. The isolation of this bacterium was carried out using Luria-Bertani (LB) broth media from environmental samples collected from oil-contaminated sites in Dhaka City. Screening tests, including the oil spreading method and drop collapse assay, were conducted to identify potential biosurfactant-producing strains, leading to the selection of E. quasihormaechei strain BDIFST24001 based on its favourable performance. Subsequent molecular identification revealed a high similarity of the strain’s 16S rRNA gene to E. quasihormaechei , which was corroborated through phylogenetic analysis. Further analysis of the biosurfactant produced by this strain indicated its rhamnolipid nature, as confirmed by FT-IR spectroscopy. The rhamnolipids exhibited promising surface-active properties, including a significant reduction in surface tension and emulsification activity, as evidenced by surface tension measurements and emulsification index assays. Optimization studies revealed that the optimal conditions for rhamnolipid production by E. quasihormaechei strain BDIFST24001 were a temperature of 37 °C, pH 10.0 and salinity of 4 %. The rhamnolipids produced by this strain demonstrated effective oil remediation capabilities, as observed through controlled experiments using petrol oil. The rhamnolipids effectively reduced the surface tension of the oil–water interface, facilitating the dispersion and emulsification of the oil phase in water. Overall, our findings highlight the potential of E. quasihormaechei strain BDIFST24001 as a promising candidate for biosurfactant-mediated oil spill cleanup and environmental remediation efforts.

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  1. Thank you for responding to the reviewer and editorial comments in a point by point manner. Two issues remain unresolved; 1) The lack of detail given for the methodology of biochemical tests used. Your rebuttal states that adding in methodology details to this manuscript does not add value. To the contrary, having full methodology details does indeed add to a manuscript, making the methods usable by readers. Please add these experimental details to your manuscript, rather than simply referencing 1000 plus page manual that others may not have access to. If you feel this makes the methodology section within the manuscript too long, feel free to include as a supplementary file. 2) The data summary only mentions the availability of your sequence data and not all underlying data which contributed to your manuscript. This was part of my editorial comments during the last revision, which I have re-copied below for your convenience. This statement is not about the removal of any ethics statements from your manuscript, which you response seems to suggest. Editor comments from previous review- "In line with Access Microbiology Open Data policies, please deposit all underling raw data (including all replicate data points) into an appropriate repository or supplementary file. Further information can be found here- https://www.microbiologyresearch.org/open-data." Please deposit all underlying raw data in an open access repository of your choice, or add it as a supplementary file to your submission. and update the data availability statement accordingly.

  2. In addition to responding to all reviewer comments, amendments are needed to figure legends. Please give details on number of replicates and what error bars represent etc. Figure 9 needs to be remade- the X axis labels cannot be read, the y axis is not labelled at all, and the use of 3D bar plots are inappropriate. Please change this to a standard 2D plot. In line with Access Microbiology Open Data policies, please deposit all underling raw data (including all replicate data points) into an appropriate repository or supplementary file. Further information can be found here- https://www.microbiologyresearch.org/open-data.

  3. Comments to Author

    During the sample collection and storage process, were contamination control and environmental condition monitoring conducted? What quality control steps were used during DNA extraction and PCR amplification to ensure the purity of the DNA and the specificity of the primers? In the section discussing the mechanism of action of rhamnolipids in oil spill remediation, the study claims that increasing the concentration of rhamnolipids does not significantly affect the activity of E. quasihormaechei strain BDIFST24001. How was this conclusion reached, and were there any quantitative measurements or controls used to verify this claim? A detailed explanation of the experimental setup and statistical validation of these results is needed.

    Please rate the manuscript for methodological rigour

    Good

    Please rate the quality of the presentation and structure of the manuscript

    Good

    To what extent are the conclusions supported by the data?

    Strongly support

    Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?

    No

    Is there a potential financial or other conflict of interest between yourself and the author(s)?

    No

    If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?

    Yes

  4. Comments to Author

    This manuscript provides a good overview of characterisation of an interesting strain with potential industrial applications - there are some edits to improve the ability for future researchers to follow your work: Lysogeny broth is more correct 70 - 90 has a lot of the same information repeated 140 - more details need to be given here, even in brief - it is too broad of an area to be left to a reference. 142 - more detail on boiling method required 150 what alignment method was used - muscle or newick? 294 the BATH assay 412 - the type of GC required - FID or MS

    Please rate the manuscript for methodological rigour

    Good

    Please rate the quality of the presentation and structure of the manuscript

    Satisfactory

    To what extent are the conclusions supported by the data?

    Partially support

    Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?

    No

    Is there a potential financial or other conflict of interest between yourself and the author(s)?

    No

    If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?

    Yes