Functional and Evolutionary Characterization of a Gene Transfer Agent's Multilocus "Genome"

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Gene transfer agents (GTAs) are phage-like particles transferring host DNA, posing evolutionary questions about their origin and function.
• The Rhodobacter capsulatus GTA (RcGTA) system involves a prophage-like gene cluster, but its genetic makeup and evolutionary history remain unclear.

Purpose of the Study:

• To elucidate the genetic organization and evolutionary origins of the Rhodobacter capsulatus gene transfer agent (RcGTA).
• To determine the functional roles of specific RcGTA gene loci and understand the evolutionary dynamics of these elements.

Main Methods:

• Transcriptomic, genetic, and biochemical analyses were employed.
• Investigated the RcGTA genome structure, distribution, and evolutionary histories within Rhodobacterales.
• Assessed the roles of specific gene loci in RcGTA production and function.

Main Results:

• The RcGTA genome comprises at least 24 genes across five distinct loci.
• Two loci are crucial for cell recognition/binding, and one for particle production/maturation.
• While widespread in Rhodobacterales, RcGTA loci exhibit varied evolutionary histories, with two showing evidence of frequent gene transfer.

Conclusions:

• RcGTA is unlikely to be a selfish genetic element; findings support it being a virus-derived element providing a selective advantage through within-population gene exchange.
• The modular nature of the RcGTA genome suggests host-driven selection to maintain gene transfer functionality.
• RcGTA represents a fascinating example of viral elements being repurposed for host benefit.