Spontaneously Induced Prophages in Lactobacillus gasseri Contribute to Horizontal Gene Transfer

Abstract

ABSTRACTLactobacillus gasseriis an endogenous species of the human gastrointestinal tract and vagina. With recent advances in microbial taxonomy, phylogenetics, and genomics,L. gasseriis recognized as an important commensal and is increasingly being used in probiotic formulations.L. gasseristrain ADH is lysogenic and harbors two inducible prophages. In this study, prophage ϕadh was found to spontaneously induce in broth cultures to populations of ∼107PFU/ml by stationary phase. The ϕadh prophage-cured ADH derivative NCK102 was found to harbor a new, second inducible phage, vB_Lga_jlb1 (jlb1). Phage jlb1 was sequenced and found to be highly similar to the closely related phage LgaI, which resides as two tandem prophages in the neotype strainL. gasseriATCC 33323. The common occurrence of multiple prophages inL. gasserigenomes, their propensity for spontaneous induction, and the high degree of homology among phages within multiple species ofLactobacillussuggest that temperate bacteriophages likely contribute to horizontal gene transfer (HGT) in commensal lactobacilli. In this study, the host ranges of phages ϕadh and jlb1 were determined against 16L. gasseristrains. The transduction range and the rate of spontaneous transduction were investigated in coculture experiments to ascertain the degree to which prophages can promote HGT among a variety of commensal and probiotic lactobacilli. Both ϕadh and jlb1 particles were confirmed to mediate plasmid transfer. As many as ∼103spontaneous transductants/ml were obtained. HGT by transducing phages of commensal lactobacilli may have a significant impact on the evolution of bacteria within the human microbiota.