Lysogenic life style of microbiota phages
It was previously suggested that human gut viromes are dominated
by temperate phages, capable of lysogenic life cycles (Breitbart
et al. 2003; Reyes et al. 2010; Minot et al. 2011). Our data indeed
show a significant subset of phages capable of a lysogenic lifestyle
in the human gut: In 244 (24.6%) of the phage contigs we identified,
an ORF with homology with an integrase or a recombinase
was detected, indicative of ability for integration into a bacterial
genome (Methods; Supplemental Data Set S4). To further identify
evidence for a lysogenic life cycle, we looked for cases in which the
assembled phage contigs also contained flanking sequences
showing identity with one of 350 sequenced human microbiome
genomes. For 135 phage contigs (13.6%), such evidence of prophage
integration into a bacterial genome was found in at least one
of the 124 individuals sampled (Fig. 1A; Supplemental Data Set S6).
Taxonomically, the hosts of these prophages belonged primarily to
the gut dominant phyla Bacteroidetes and Firmicutes, in congruence
with previous observations (Supplemental Data Set S6; Reyes et al.
2010). In all cases in which the bacterial host of the phage was
inferred both through a CRISPR array and through prophage integration,
inferences were in close agreement (Supplemental Data
Set S6).