Independent host- and bacterium-based determinants protect a model symbiosis from phage predation

Bacteriophages (phages) are diverse and abundant constituents of microbial communities worldwide, capable of modulating bacterial populations in diverse ways. Here, we describe the phage HNL01, which infects the marine bacterium Vibrio fischeri. We use culture-based approaches to demonstrate that mutations in the exopolysaccharide locus of V. fischeri render this bacterium resistant to infection by HNL01, highlighting the extracellular matrix as a key determinant of HNL01 infection. Additionally, using the natural symbiosis between V. fischeri and the squid Euprymna scolopes, we show that, during colonization, V. fischeri is protected from phages present in the ambient seawater. Taken together, these findings shed light on independent yet synergistic host-and bacterium-based strategies for resisting symbiosis-disrupting phage predation, and we present important implications for understanding these strategies in the context of diverse host-associated microbial ecosystems.

Automated summary

In this study, the phage HNL01 that infects marine bacterium Vibrio fischeri was described. Mutations in the exopolysaccharide locus of V. fischeri were found to render this bacterium resistant to HNL01 infection. Additionally, it was shown that V. fischeri is protected from phages present in the ambient seawater during colonization.