Large Variabilities in Host Strain Susceptibility and Phage Host Range Govern Interactions between Lytic Marine Phages and Their Flavobacterium Hosts

Abstract

Phages are a main mortality factor for marine bacterioplankton and are thought to regulate bacterial community composition through host-specific infection and lysis. In the present study we demonstrate for a marine phage-host assemblage that interactions are complex and that specificity and efficiency of infection and lysis are highly variable among phages infectious to strains of the same bacterial species. Twenty-three Bacteroidetes strains and 46 phages from Swedish and Danish coastal waters were analyzed. Based on genotypic and phenotypic analyses, 21 of the isolates could be considered strains of Cellulophaga baltica (Flavobacteriaceae). Nevertheless, all bacterial strains showed unique phage susceptibility patterns and differed by up to 6 orders of magnitude in sensitivity to the same titer of phage. The isolated phages showed pronounced variations in genome size (8 to >242 kb) and host range (infecting 1 to 20 bacterial strains). Our data indicate that marine bacterioplankton are susceptible to multiple co-occurring phages and that sensitivity towards phage infection is strain specific and exists as a continuum between highly sensitive and resistant, implying an extremely complex web of phage-host interactions. Hence, effects of phages on bacterioplankton community composition and dynamics may go undetected in studies where strain identity is not resolvable, i.e., in studies based on the phylogenetic resolution provided by 16S rRNA gene or internal transcribed spacer sequences.

Viral and microbial community dynamics in four aquatic environments

“…This was observed by the fine-grained recA analyses showing rapid change at the level of microbial strains. These conclusions are consistent with many other studies (Middelboe, 2000;Middelboe et al, 2001;Zhong et al, 2002;Bull et al, 2006;Holmfeldt et al, 2007;Stoddard et al, 2007). Our conclusions are also supported by a recent study linking phage predation to the persistence of microbial diversity at the strain level .…”

Effects of patch connectivity and heterogeneity on metacommunity structure of planktonic bacteria and viruses

“…Our sampling procedures may have partially excluded such viruses, given that samples were filtered over 0.22 mm filters and then shock frozen, which facilitates the break-up of large viruses. Patterns of association may also be reduced if viral communities show low host specificity (Sano et al, 2004;Holmfeldt et al, 2007). Prokaryotic hosts may also be infected by multiple viruses (Holmfeldt et al, 2007) and, given the high reproduction potential of viruses, viral communities can show rapid compositional turnover rates leading to poor associations between bacterial and viral communities.…”

La « synergie phages-antibiotiques »

“…Heureusement, les bactéries sont aussi victimes de prédateurs naturels puisque, comme tous les autres organismes vivants, elles peuvent être infectées par des virus. Ces virus de bactéries, les bactériophages ou phages, sont très spécifiques ; ils infectent en général une seule espèce de bactérie et même souvent seulement certaines souches de l'espèce [1,2]. Presque toutes les espèces bactériennes peuvent être infectées par de nombreux phages différents.…”