Filamentous phages reduce bacterial growth in low salinities

Abstract

Being non-lytic, filamentous phages can replicate at high frequencies and often carry virulence factors, which are important in the evolution and emergence of novel pathogens. However, their net effect on bacterial fitness remains unknown. To understand the ecology and evolution between filamentous phages and their hosts, it is important to assess (i) fitness effects of filamentous phages on their hosts and (ii) how these effects depend on the environment. To determine how the net effect on bacterial fitness by filamentous phages changes across environments, we constructed phage–bacteria infection networks at ambient 15 practical salinity units (PSU) and stressful salinities (11 and 7 PSU) using the marine bacterium, Vibrio alginolyticus and its derived filamentous phages as model system. We observed no significant difference in network structure at 15 and 11 PSU. However, at 7 PSU phages significantly reduced bacterial growth changing network structure. This pattern was mainly driven by a significant increase in bacterial susceptibility. Our findings suggest that filamentous phages decrease bacterial growth, an indirect measure of fitness in stressful environmental conditions, which might impact bacterial communities, alter horizontal gene transfer events and possibly favour the emergence of novel pathogens in environmental Vibrios.

Filamentous Pseudomonas Phage Pf4 in the Context of Therapy-Inducibility, Infectivity, Lysogenic Conversion, and Potential Application

“…Filamentous phages usually reduce bacterial growth, as reported for Xanthomonas citri [34,35], Xanthomonas campestris [36], Ralstonia solanacearum [37], Pseudoalteromonas [38], Vibrio alginolyticus [39], and E. coli [40,41]. However, there are known cases where filamentous phages do not affect the growth of their host as in X. campestris [42], R. solanacearum [43], and Yersinia pestis [44].…”

Higher phage virulence accelerates the evolution of host resistance

“…We quantified resistance to the respective ancestral phage by determining the reduction in bacterial growth rate (RBG) imposed by the phage, adapted from [24] with some modifications according to [25]. Twenty-four random colonies from each population from transfers T0, T1, T2, T6, T12, T18, T24 and T30 were introduced into 96-well microtiter plates containing Medium101 at a concentration of 5 × 10 6 cells ml −1 and inoculated with approximately 2.5 × 10 6 PFU ml -1 of the respective ancestral phage used for the selection experiment or without phage (control).…”

Higher phage virulence accelerates the evolution of host resistance

“…We quantified the bacteria could not get infected by the respective ancestral phage by determining the reduction in bacterial growth rate (RBG) imposed by the phage, adapted from (Poullain, Gandon et al 2008) with some modifications according to (Goehlich, Roth et al 2019). Twenty-four random colonies from each population from transfer T0, T1, T2, T6, T12, T18, T24, and T30 were introduced into 96-well microtiter plates containing Medium101 at a concentration of 5×10 6 cells/ml and inoculated with ~2.5×10 6 PFU/ml of the respective ancestral phage used for the selection experiment or without phage (control).…”