Ancient Darwinian replicators nested within eubacterial genomes

Area of Science:

• Microbiology
• Genetics
• Evolutionary Biology

Background:

• Mobile genetic elements (MGEs) like transposons and insertion sequences typically have short persistence times within bacterial lineages.
• Long-term MGE survival usually relies on horizontal gene transfer to new hosts.
• Theoretically, MGEs persisting for millions of years via vertical inheritance should not exist.

Purpose of the Study:

• To investigate REPINs, a class of non-autonomous MGEs, as a potential exception to typical MGE persistence.
• To test the hypothesis that REPINs form enduring, beneficial associations with bacterial chromosomes.
• To explore the evolutionary implications of REPINs' unique replication strategy.

Main Methods:

• Comparative analysis of REPINs and typical MGEs.
• Examination of REPIN replication rates and population dynamics.
• Analysis of REPIN conservation in relation to RAYT transposase function.
• Investigation of REPIN diversity accumulation within host lineages.
• Study of REPIN abundance and diversity patterns in bacterial species.

Main Results:

• REPIN replication rates are significantly lower than those of typical MGEs.
• REPIN population sizes fluctuate with available genome space.
• REPIN conservation is dependent on the function of RAYT transposases.
• REPIN diversity accumulates within host lineages, suggesting vertical inheritance.
• Patterns of REPIN abundance and diversity support a mutualistic association hypothesis.

Conclusions:

• REPINs represent a unique class of MGEs that form enduring, mutually beneficial associations with eubacterial chromosomes.
• REPINs exhibit characteristics analogous to mutualistic endosymbiotic bacteria.
• The findings challenge traditional MGE evolution models and highlight a novel mode of genetic element persistence.