Spatial propagation of temperate phages within and among biofilms

Abstract

Bacteria commonly form groups comprised of thousands or millions of cells and secreted adhesive matrix that controls their spatial organization. These groups – termed biofilms – can act as refuges from exogenous threats, both abiotic, such as exposure to antibiotics, and biotic, including predatory bacteria and bacteriophages. Unlike their obligate lytic counterparts that can only lyse and kill their host after infection, temperate phages can either lyse their host cell to produce a burst of new virions, or they can lysogenize their hosts by integrating their genome into that of infected bacteria replicate their genetic content vertically as hosts grow and divide, while also retaining the ability to enter the lytic cycle in response to environmental cues. Despite the ubiquity of both temperate phages and bacterial biofilms, the fundamental patterns of temperate phage propagation in the context of biofilm growth have never been explored on cellular spatial scales. Here, we leverage anE. colihost and an engineered λ phage that produces distinct fluorescent protein reporters to enable visual differentiation between lytic and lysogenic infections. We determine that lysogeny within establishedE. colibiofilms occurs within a predictable region of cell density, generally on the periphery of large groups of cells in the midst of a wave of lytic infections. Because lysogenization by λ occurs in the midst of a wave of lytic infections that locally decrease biofilm integrity, we found that lysogenized hosts are predisposed to higher dispersal to new locations. As a result of this predisposition towards dispersal, biofilms formed downstream of the original area of phage exposure have a significantly increased proportion of lysogens. A comparison of our results with those for obligate lytic phages reveals that the temperate phage life history confers unique and previously unknown advantages of proliferation within spatially constrained and architecturally heterogeneous biofilm communities. Our findings also bear on the conditions under which temperate phages may be used to manipulate host biofilm formation in the context of novel antimicrobial phage therapeutics.

Phollow: Visualizing Gut Bacteriophage Transmission within Microbial Communities and Living Animals

“…Previous approaches using fluorescently marked virions have uncovered amazing details of phage biology 24,[35][36][37][38] . However, comprehending the impacts of phages on microbiomes requires additional strategies for capturing phage replication and transmission across space, time, and complexity.…”