Abstract

Numerous ecological interactions among microbes – for example, competition for space and resources, or interaction among phages and their bacterial hosts – are likely to occur simultaneously in multispecies biofilm communities. While biofilms formed by just a single species occur, multispecies biofilms are thought to be more typical of microbial communities in the natural environment. Previous work has shown that multispecies biofilms can increase, decrease, or have no measurable impact on phage exposure of a host bacterium living alongside another species that the phages cannot target. The reasons causing this variability are not well understood, and how phage-host encounters change within multispecies biofilms remains mostly unexplored at the cellular spatial scale. Here, we explore how the microscale biofilm structure of a model 2-species biofilms impacts cell-cell and cell-phage interactions underlying larger population wide patterns. Our system consists of dual-culture biofilms of Escherichia coli and Vibrio cholerae under exposure to T7 phages or λ phages. In the absence of phages, the two species compete with each other for limited space and resources. As shown previously, sufficiently mature biofilms of E. coli can protect themselves from phage exposure via their curli matrix. Before this stage of biofilm structural maturity, E. coli is highly susceptible to phages, however we show that these bacteria can gain lasting protection against phage exposure if they have become embedded within highly packed groups of V. cholerae in co-culture. In this manner, E. coli cells that are otherwise susceptible to T7 and λ phages can survive phage exposure in the absence of de novo resistance evolution. While co-culture growth allows for earlier protection from phages conferred by V. cholerae cells, it comes at the cost of competing with V. cholerae and a disruption of normal curli-mediated protection for E. coli even in dual species biofilms grown over long time scales.

J. B. Cavanagh

Publications