Abstract
Bacteroides spp. are part of the human intestinal microbiota but can under some circumstances become clinical pathogens. Phages are a potentially valuable therapeutic treatment option for many pathogens, but phage therapy for pathogenic Bacteroides spp. including Bacteroides fragilis is currently limited to three genome-sequenced phages. Here we describe the isolation from sewage wastewater and genome of a lytic phage, vB_BfrS_23, that infects and kills B. fragilis strain GB124. Transmission electron microscopy identified this phage as a member of the Siphoviridae family. The phage is stable when held at temperatures of 4 and 60°C for 1 h. It has a very narrow host range, only infecting one host from a panel of B. fragilis strains (n = 8). Whole-genome sequence analyses of vB_BfrS_23 determined it is double-stranded DNA phage and is circularly permuted, with a genome of 48,011 bp. The genome encodes 73 putative open reading frames. We also sequenced the host bacterium, B. fragilis GB124 (5.1 Mb), which has two plasmids of 43,923 and 4,138 bp. Although this phage is host specific, its isolation together with the detailed characterization of the host B. fragilis GB124 featured in this study represent a useful starting point from which to facilitate the future development of highly specific therapeutic agents. Furthermore, the phage could be a novel tool in determining water (and water reuse) treatment efficacy, and for identifying human fecal transmission pathways within contaminated environmental waters and foodstuffs.
Highlights
Bacteriophages are viruses that infect bacterial cells and as a result can influence their growth, fitness and response to stress (Casjens and Hendrix, 2015; Davies et al, 2016)
Bacteroides fragilis GB124 was used as a host for phage discovery and the starting point for the screening of a filtered raw wastewater sample
We identified and isolated a virulent phage capable of infecting GB124, that generated plaques that ranged in size between 0.5 and 2 mm (Figure 1A)
Summary
Bacteriophages (phage) are viruses that infect bacterial cells and as a result can influence their growth, fitness and response to stress (Casjens and Hendrix, 2015; Davies et al, 2016). They are estimated to be numerically the most abundant biological entity on earth numbering at least 1031 (Hendrix et al, 1999; Bar-On et al, 2018). In a recent study looking at 98 gut samples the relative abundance of Bacteroides spp. ranged from 0.37 to 98.82% (King et al, 2019). Bacteroides spp. confer significant health benefits to their host including the digestion, processing and extraction of nutrients from complex plant-based polysaccharides, promoting colonic motility and angiogenesis, and the development of the gut-associated immune system (Hooper et al, 2003; Xu et al, 2003; Mazmanian et al, 2005)
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