Imaging flow cytometry reveals a dual role for exopolysaccharides in biofilms: To promote self-adhesion while repelling non-self-community members

Harsh Maan; Tatyana L Povolotsky; Ziv Porat; Maxim Itkin; Sergey Malitsky; Ilana Kolodkin-Gal

doi:10.1016/j.csbj.2021.11.043

Imaging flow cytometry reveals a dual role for exopolysaccharides in biofilms: To promote self-adhesion while repelling non-self-community members

Comput Struct Biotechnol J. 2021 Dec 4:20:15-25. doi: 10.1016/j.csbj.2021.11.043. eCollection 2022.

Authors

Harsh Maan¹, Tatyana L Povolotsky¹, Ziv Porat², Maxim Itkin³, Sergey Malitsky³, Ilana Kolodkin-Gal¹

Affiliations

¹ Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
² Flow Cytometry Unit, Life Sciences Core Facilities, Weizmann Institute of Science, Rehovot, Israel.
³ Life Science Core Facilities Weizmann Institute of Science, 234 Herzl Street, Rehovot, Israel.

Abstract

In nature, bacteria frequently reside in differentiated communities or biofilms. These multicellular communities are held together by self-produced polymers that allow the community members to adhere to the surface as well as to neighbor bacteria. Here, we report that exopolysaccharides prevent Bacillus subtilis from co-aggregating with a distantly related bacterium Bacillus mycoides, while maintaining their role in promoting self-adhesion and co-adhesion with phylogenetically related bacterium, Bacillus atrophaeus. The defensive role of the exopolysaccharides is due to the specific regulation of bacillaene. Single cell analysis of biofilm and free-living bacterial cells using imaging flow cytometry confirmed a specific role for the exopolysaccharides in microbial competition repelling B. mycoides. Unlike exopolysaccharides, the matrix protein TasA induced bacillaene but inhibited the expression of the biosynthetic clusters for surfactin, and therefore its overall effect on microbial competition during floating biofilm formation was neutral. Thus, the exopolysaccharides provide a dual fitness advantage for biofilm-forming cells, as it acts to promote co-aggregation of related species, as well as, a secreted cue for chemical interference with non-compatible partners. These results experimentally demonstrate a general assembly principle of complex communities and provides an appealing explanation for how closely related species are favored during community assembly. Furthermore, the differential regulation of surfactin and bacillaene by the extracellular matrix may explain the spatio-temporal gradients of antibiotic production within biofilms.

Keywords: Biofilms; CM, Conditioned medium; ECM, Extracellular matrix; Extracellular matrix; Gene regulation; Imaging flow cytometry; LC-MS, Liquid chromatography–mass spectrometry; NRPs, Nonribosomal peptides; PKS, Polyketides; WT, Wild type.