Novel integrative elements and genomic plasticity in ocean ecosystems

Horizontal gene transfer accelerates microbial evolution. The marine picocyanobacterium Prochlorococcus exhibits high genomic plasticity, yet the underlying mechanisms are elusive. Here, we report a novel family of DNA transposons-tycheposons-some of which are viral satellites while others carry cargo, such as nutrient-acquisition genes, which shape the genetic variability in this globally abundant genus. Tycheposons share distinctive mobile-lifecycle-linked hallmark genes, including a deep-branching site-specific tyrosine recombinase. Their excision and integration at tRNA genes appear to drive the remodeling of genomic islands-key reservoirs for flexible genes in bacteria. In a selection experiment, tycheposons harboring a ni-trate assimilation cassette were dynamically gained and lost, thereby promoting chromosomal rearrange-ments and host adaptation. Vesicles and phage particles harvested from seawater are enriched in tychepo-sons, providing a means for their dispersal in the wild. Similar elements are found in microbes co-occurring with Prochlorococcus, suggesting a common mechanism for microbial diversification in the vast oligotrophic oceans.

Automated summary

Horizontal gene transfer plays a crucial role in microbial evolution, and the newly discovered tycheposons, a family of DNA transposons, are found to be key drivers of genomic remodeling. Tycheposons are widely distributed in the marine environment and are dispersed through vesicles and phage particles. Similar elements are also found in microbes co-existing with Prochlorococcus, suggesting a common mechanism for microbial diversification in the vast oligotrophic oceans.