A new Serratia taxon found in a trombidiform mite shows genomic evidence of host adaptation but is phylogenetically distinct from Serratia symbiotica

A new Serratia taxon has been discovered in a trombidiform mite, Halotydeus destructor, according to a recent study. The researchers identified this putative new species using metagenomic approaches, which involve analyzing genetic material collected directly from an environmental sample. The newfound Serratia sp. exhibits genomic evidence of a possible transition to a host-adapted lifestyle, suggesting a parallel evolutionary path to the well-known Serratia symbiotica species, which is known to associate with aphids.

However, this new Serratia taxon differs phylogenetically from S. symbiotica, as it belongs to a clade of free-living Serratia species. The researchers observed genomic signatures indicative of the transition to a host-adapted lifestyle in the new Serratia sp., such as a reduced genome size and coding capacity, an elevated fraction of transposases, and detectable chromosomal rearrangements.

These genomic features distinguish the new species from other free-living Serratia species. Despite the genomic evidence of a host-adapted lifestyle, the new Serratia sp. does not exhibit the same degree of genome reduction as S. symbiotica. Functional gene content analyses, including categories of cellular functions (COGs) and virulence factors, revealed a distinct gene profile for the new Serratia sp. compared to both free-living Serratia species.

Moreover, the study suggests that infections caused by the new Serratia sp. are prevalent in wild populations of H. destructor across its invasive Australian range. The findings underscore the importance of further investigating the potential role this symbiont might play in the evolutionary ecology of its mite host.