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Bacteria acquire new genes by horizontal gene transfer, typically mediated by mobile genetic elements (MGEs). While plasmids, bacteriophages, and certain integrative and conjugative elements are well characterized, the broader diversity of MGEs remains poorly understood. Here, we cultured the bacterium Pseudomonas fluorescens SBW25 with sterile filtrate obtained from garden compost communities. Genome sequencing of derived colonies revealed acquisition of three different mobile elements, each integrated immediately downstream of tmRNA , each flanked by direct repeats, and each encoding a tyrosine integrase ( intY ) plus putative phage defense systems. Absent are genes with recognized roles in autonomous transfer. Interrogation of DNA sequence databases showed that similar elements are widespread in the genus Pseudomonas and beyond, with Vibrio Pathogenicity Island-1 from Vibrio cholerae as a notable example. Bioinformatic analyses reveal evidence of extensive horizontal transfer among diverse hosts. Detailed analysis of a single element, I55, showed that it is transferred between cells by jumbo phages, and confers fitness benefits via a type II restriction-modification system.
Zhao et al. (Tue,) studied this question.