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

Abstract

Bacteria are thought to often occupy environments with many other microbial species with which they interact extensively, including during biofilm formation. Adherence to surfaces and secretion of extracellular matrix is common in the microbial world, and we are still learning how the rich variety of ecological interactions that dictate biofilm structure and community ecology occur at the cellular scale. Here we explore an especially understudied element of biofilm ecology, namely predation by the bacterium Bdellovibrio bacteriovorus. This predator can kill and consume many different Gram-negative bacteria, including Vibrio cholerae and Escherichia coli. V. cholerae can protect itself from predation within highly packed biofilm structures that it creates, whereas E. coli biofilms are generally highly susceptible to predation by B. bacteriovorus. We were curious here how predator-prey dynamics might change if V. cholerae and E. coli are growing in biofilms together before exposure to B. bacteriovorus. We first find that in dual species prey biofilms, E. coli predation survival increases, whereas V. cholerae survival decreases. The benefit E. coli gains occurs when they become embedded within expanding groups of highly packed V. cholerae. But we find, interestingly, that normal, ordered and highly packed biofilm structure of V. cholerae can be disrupted if V. cholerae cells are directly adjacent to E. coli cells at the start of biofilm growth. When this occurs, the two species become entangled, and V. cholerae cannot coordinate its normal cell-cell alignment and matrix secretion that control the production of its normally ordered architecture. The resulting, disordered cell groups of the two species are viable and can grow into large groups, but they are no longer protected from predation; the loss of this portion of the V. cholerae population accounts for the decrease in predation protection they incur when in co-culture with E. coli. Because biofilm cell group structure depends on initial cell distributions at the start of prey biofilm growth, the colonization dynamics have a dramatic impact on the eventual multispecies biofilm architecture, which in turn determines to what extent both species survive exposure to B. bacteriovorus. Our study highlights the deep connections between the mechanics of biofilm architectural development, dispersal/colonization ecology, and population dynamics of predator-prey interaction in microbial systems, in addition to raising new important questions in each of these domains.

Multispecies biofilm architecture determines bacterial exposure to phages

“…cholerae fluorescence was indeed significantly elevated in close proximity to E. coli after phage exposure, representing the surviving, protected portion of the E. coli population embedded within groups of V. cholerae. This protection effect could be replicated when introducing λ phages instead of T7 phages (S3 Fig) , and in a parallel study, we show that the same effect occurs under predation by the bacterium B. bacteriovorus [64].…”

“…This protection effect could be replicated when introducing λ phages instead of T7 phages ( S3 Fig ), and in a parallel study, we show that the same effect occurs under predation by the bacterium B . bacteriovorus [ 64 ].…”

“…coli only disrupts V . cholerae architecture when cells of both species begin dividing directly adjacent to each other from the outset of biofilm growth [ 64 ].…”

Multispecies biofilm architecture determines bacterial exposure to phages

“…Compared to control experiments with no phages (Fig 1C), V. cholerae fluorescence was indeed significantly elevated in close proximity to E. coli after phage exposure, representing the surviving, protected portion of the E. coli population embedded within groups of V. cholerae . This protection effect could be replicated when introducing λ phages instead of T7 phages (SI Figure S3), and in a parallel study we show that the same effect occurs under predation by the bacterium B. bacteriovorus (Wucher et al, 2022, bioRxiv ) 62 .…”

“…This suggests that the V. cholerae biofilm architecture, once initiated, can force cell groups of other species trapped within them into high packing orientations that do not disrupt the overall structure (SI Fig S9) 40,43,66,67 . As we explored in a parallel study on B. bacteriovorus predation in dual species biofilms, coculture with E. coli only disrupts V. cholerae architecture when cells of both species begin dividing directly adjacent to each other from the outset of biofilm growth (Wucher et al, 2022, bioRxiv) 62 .…”