Parallel Evolution of Bacteroidota as Long-Term Endosymbionts of Insects.

Bacteroidota independently evolved into highly specialized insect endosymbionts with minimal genomes, exhibiting parallel gene degradation across diverse scale insect lineages.

• Why it matters: Understanding how microbial clades diversify and evolve within hosts is limited, especially beyond well-studied groups like Pseudomonadota, hindering insights into symbiosis origins and stability.
• What they did: The study analyzed extensive genome samples from scale insects, revealing the stepwise transition of Bacteroidota from recent host-associated bacteria to long-term, highly specialized endosymbionts with reduced gene sets.
• The result: Findings show a recurrent evolutionary pathway with symbionts maintained for hundreds of millions of years, suggesting that initial host-symbiont compatibility influences long-term symbiosis outcomes.