Abstract The Sodalis genus exhibits a wide range of symbiotic associations with insects, from facultative to obligate relationships, reflecting transitions from free-living to host-dependent lifestyles. We report the draft genome of Sodalis sp., which we named mRsS25, recovered from the metagenome of Russelliana solanicola , the South American potato psyllid. The 1.42 Mb genome (G + C content: 45.6%) encodes 1,010 proteins, 38 tRNAs, and 4 rRNAs. The mRsS25 MAG harbored 142 pseudogenes enriched in mobile genetic element-related features, closely matching mildly reduced Sodalis genomes (e.g., S. glossinidius and Candidatus S. pierantonianus SOPE) and showing greatest functional similarity to this intermediate group. Phylogenomic, orthologous clustering, and average nucleotide identity analyses provide evidence that mRsS25 is a new Sodalis species, separate from other Sodalis species from tsetse flies and psyllids. An integrated metabolic analysis of mRsS25 and its psyllid host, R. solanicola , was conducted to infer the nature of their symbiotic relationship. The symbiont retains significant metabolic autonomy but shows evidence of reductive evolution, particularly in amino acid synthesis pathways that are present in the host. The pattern of gene losses in the mRsS25 genome suggests an increasing metabolic dependency, adaptation to a protected niche, and the simplification of complex regulatory networks. Our results suggest a nutritional mutualism involving both metabolic complementarity (e.g., symbiont-specific riboflavin synthesis) and redundancy (e.g., biotin and folate pathways). Additionally, the symbiont may convert excess host-derived sugar to acetate, which may serve as a substrate for host lipogenesis. These findings provide insights into insect-microbe symbioses and Sodalis evolution.
Borbón-Cortés et al. (Mon,) studied this question.