Breakdown of clonal cooperative architecture in multispecies biofilms and the spatial ecology of predation.

Abstract

Biofilm formation, including adherence to surfaces and secretion of extracellular matrix, is common in the microbial world, but we often do not know how interaction at the cellular spatial scale translates to higher-order biofilm community ecology. Here we explore an especially understudied element of biofilm ecology, namely predation by the bacterium <i>Bdellovibrio bacteriovorus</i>. This predator can kill and consume many different Gram-negative bacteria, including <i>Vibrio cholerae</i> and <i>Escherichia coli</i>. <i>V. cholerae</i> can protect itself from predation within densely packed biofilm structures that it creates, whereas <i>E. coli</i> biofilms are highly susceptible to <i>B. bacteriovorus</i>. We explore how predator-prey dynamics change when <i>V. cholerae</i> and <i>E. coli</i> are growing in biofilms together. We find that in dual-species prey biofilms, <i>E. coli</i> survival under <i>B. bacteriovorus</i> predation increases, whereas <i>V. cholerae</i> survival decreases. <i>E. coli</i> benefits from predator protection when it becomes embedded within expanding groups of highly packed <i>V. cholerae</i>. But we also find that the ordered, highly packed, and clonal biofilm structure of <i>V. cholerae</i> can be disrupted if <i>V. cholerae</i> cells are directly adjacent to <i>E. coli</i> cells at the start of biofilm growth. When this occurs, the two species become intermixed, and the resulting disordered cell groups do not block predator entry. Because biofilm cell group structure depends on initial cell distributions at the start of prey biofilm growth, the surface colonization dynamics have a dramatic impact on the eventual multispecies biofilm architecture, which in turn determines to what extent both species survive exposure to <i>B. bacteriovorus.</i>