Bacterial predation transforms the landscape and community assembly of biofilmsHighlights d Biofilms with high cell packing are protected from bacterial predator access d The protection effect strongly alters biofilm microlandscapes after predation d Predation on the periphery of biofilms loosens their local architecture d These changes in biofilm structure allow other bacteria to invade prey biofilms

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.

Micavibrio aeruginosavorus is an obligate Gram-negative predatory bacterial species that feeds on other Gram-negative bacteria by attaching to the surface of its prey and feeding on the prey’s cellular contents. In this study, Serratia marcescens with defined mutations in genes for extracellular cell structural components and secreted factors were used in predation experiments to identify structures that influence predation. No change was measured in the ability of the predator to prey on S. marcescens flagella, fimbria, surface layer, prodigiosin and phospholipase-A mutants. However, higher predation was measured on S. marcescens metalloprotease mutants. Complementation of the metalloprotease gene, prtS, into the protease mutant, as well as exogenous addition of purified serralysin metalloprotease, restored predation to wild type levels. Addition of purified serralysin also reduced the ability of M. aeruginosavorus to prey on Escherichia coli. Incubating M. aeruginosavorus with purified metalloprotease was found to not impact predator viability; however, pre-incubating prey, but not the predator, with purified metalloprotease was able to block predation. Finally, using flow cytometry and fluorescent microscopy, we were able to confirm that the ability of the predator to bind to the metalloprotease mutant was higher than that of the metalloprotease producing wild-type. The work presented in this study shows that metalloproteases from S. marcescens could offer elevated protection from predation.

Purpose: Pseudomonas aeruginosa keratitis is a severe ocular infection that can lead to perforation of the cornea. In this study we evaluated the role of bacterial quorum sensing in generating corneal perforation and bacterial proliferation and tested whether co-injection of the predatory bacteria Bdellovibrio bacteriovorus could alter the clinical outcome. P. aeruginosa with lasR mutations were observed among keratitis isolates from a study collecting samples from India, so an isogenic lasR mutant strain of P. aeruginosa was included. Methods: Rabbit corneas were intracorneally infected with P. aeruginosa strain PA14 or an isogenic ΔlasR mutant and co-injected with PBS or B. bacteriovorus. After 24 h, eyes were evaluated for clinical signs of infection. Samples were analyzed by scanning electron microscopy, optical coherence tomography, sectioned for histology, and corneas were homogenized for CFU enumeration and for inflammatory cytokines. Results: We observed that 54% of corneas infected by wild-type PA14 presented with a corneal perforation (n=24), whereas only 4% of PA14 infected corneas that were co-infected with B. bacteriovorus perforate (n=25). Wild-type P. aeruginosa proliferation was reduced 7-fold in the predatory bacteria treated eyes. The ΔlasR mutant was less able to proliferate compared to the wild-type, but was largely unaffected by B. bacteriovorus. Conclusion: These studies indicate a role for bacterial quorum sensing in the ability of P. aeruginosa to proliferate and cause perforation of the rabbit cornea. Additionally, this study suggests that predatory bacteria can reduce the virulence of P. aeruginosa in an ocular prophylaxis model.

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 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 densely packed biofilm structures that it creates, whereas E. coli biofilms are highly susceptible to B. bacteriovorus . We explore how predator–prey dynamics change when V. cholerae and E. coli are growing in biofilms together. We find that in dual-species prey biofilms, E. coli survival under B. bacteriovorus predation increases, whereas V. cholerae survival decreases. E. coli benefits from predator protection when it becomes embedded within expanding groups of highly packed V. cholerae . But we also find that the ordered, highly packed, and clonal 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 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 B. bacteriovorus.

No abstract

The predatory bacterium Bdellovibrio bacteriovorus follows a life cycle in which it attaches to the exterior of a Gram-negative prey cell, enters the periplasm, and harvests resources to replicate before lysing the host to find new prey. Predatory bacteria such as this are common in many natural environments, as are groups of matrix-bound clusters of prey cells, termed biofilms. Despite the ubiquity of both predatory bacteria and biofilm-dwelling prey, the interaction between B. bacteriovorus and prey cells inside biofilms has received little attention and has not yet been studied at the micrometer scale. Filling this knowledge is critical to understanding the nature of predator-prey interaction in nature. Here we show that B. bacteriovorus is able to prey upon biofilms of the pathogen Vibrio cholerae, but only up until a critical maturation threshold past which the prey biofilms are protected from their predators. We determine the contribution of matrix secretion and cell-cell packing of the prey biofilm toward this protection mechanism. Our results demonstrate that B. bacteriovorus predation in the context of this protection threshold fundamentally transforms the sub-millimeter scale landscape of biofilm growth, as well as the process of community assembly as new potential biofilm residents enter the system.