Spatial propagation of temperate phages within and among biofilms

Abstract

AbstractBacteria commonly form groups comprised of cells and secreted adhesive matrix that controls their spatial organization. These groups – termed biofilms – can act as refuges from environmental disturbance and from attack by biotic threats, including bacteriophages (phages). Unlike obligately lytic phages that can only successfully propagate by killing their host after infection, temperate phages can either lyse and kill their host cell to release a burst of new virions, or they can lysogenize their hosts by integrating their genome into that of their hosts and replicate vertically as hosts grow and divide. Once integrated into a host genome, temperate phages retain the ability to enter the lytic cycle in response to changes in host physiological state. 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 produce distinct fluorescent protein reporters to enable visual differentiation between lytic and lysogenic infections. We determine that lysogeny within establishedE. colibiofilms most commonly occurs within a predictable region of cell group architecture. Because lysogenization by λ occurs amid a wave of lytic infections that locally decrease biofilm integrity, and because lysogens are generally found in the periphery of large groups, 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 obligately lytic phages reveals that the temperate phage life history confers unique and previously unknown advantages of proliferation in 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.