Multispecies biofilm architecture determines bacterial exposure to phages

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 underlying 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 study how the cellular scale architecture of model 2-species biofilms impacts cell-cell and cell-phage interactions controlling larger scale population and community dynamics. Our system consists of dual-culture biofilms ofEscherichia coliandVibrio choleraeunder exposure to T7 phages, which we study using microfluidic culture, high resolution confocal microscopy imaging, and detailed image analysis. As shown previously, sufficiently mature biofilms ofE. colican protect themselves from phage exposure via their curli matrix. Before this stage of biofilm structural maturity,E. coliis highly susceptible to phages, however we show that these bacteria can gain lasting protection against phage exposure if they have become embedded in the bottom layers of highly packed groups ofV. choleraein co-culture. This protection, in turn, is dependent on the cell packing architecture controlled byV. choleraebiofilm matrix secretion. In this manner,E. colicells that are otherwise susceptible to phage mediated killing can survive phage exposure in the absence ofde novoresistance evolution. While co-culture biofilm formation withV. choleraecan confer phage protection toE. coli, it comes at the cost of competing withV. choleraeand a disruption of normal curli-mediated protection forE. colieven in dual species biofilms grown over long time scales. This work highlights the critical importance of studying multispecies biofilm architecture and its influence on the community dynamics of bacteria and phages.Short blurbMultispecies bacterial biofilm architecture qualitatively alters the spatial patterns of phage exposure and the community dynamics of matrix production, interspecific competition, and phage propagation.