Filamentation ofVibrio choleraeis an adaptation for surface attachment and biofilm architecture

Abstract

Collective behavior in spatially structured groups, or biofilms, is the norm among microbes in their natural environments. Though microbial physiology and biofilm formation have been studied for decades, tracing the 25 mechanistic and ecological links between individual cell properties and the emergent features of cell groups is still in its infancy. Here we use single-cell resolution confocal microscopy to explore biofilm properties of the human pathogen Vibrio cholerae in conditions closely mimicking its marine habitat. We find that some -but not allpandemic isolates produce filamentous cells than can be over 50 µm long. This filamentous morphotype gains a profound competitive advantage in colonizing and spreading on particles of chitin, the material many marine Vibrio 30 species depend on for growth outside of hosts. Furthermore, filamentous cells can produce biofilms that are independent of all currently known secreted components of the V. cholerae biofilm matrix; instead, filamentous biofilm architectural strength appears to derive from the entangled mesh of cells themselves. The advantage gained by filamentous cells in early chitin colonization and growth is counter-balanced in longer term competition experiments with matrix-secreting V. cholerae variants, whose densely packed biofilm structures displace 35 competitors from surfaces. Overall our results reveal a novel mode of biofilm architecture that is dependent on filamentous cell morphology and advantageous in environments with rapid chitin particle turnover. This insight provides concrete links between V. cholerae cell morphology, biofilm formation, marine ecology, and -potentially -the strain composition of cholera epidemics. 40We discovered that some pandemic isolates of V. cholerae, and in particular strain CVD112 of the O139 serogroup, 75filaments aggressively under nutrient-limited conditions, including on particles of chitin in sea water. Filamentation confers markedly altered chitin colonization and biofilm architecture relative to shorter cells. Differences in chitin colonization and biofilm architecture, in turn, strongly influence competition for space and resources, suggesting that normal-length and filamentous morphotypes are fundamentally adapted to different regimes of chitin particle turnover in the water column. Overall, our results highlight a novel mode of biofilm assembly and yield new insights 80into the fundamental roles of cell shape in the marine ecology of V. cholerae. 500surface attachment and biofilm architecture