Genome-based analyses indicate that Serratia marcescens subsp. marcescens and Serratia marcescens subsp. sakuensis do not merit separation to subspecies status.

Abstract

The species Serratia marcescens currently comprises two subspecies, viz. Serratia marcescenssubsp. marcescens and Serratia marcescenssubsp. sakuensis. The latter species was created by considering the differentiating endospore-formation capability of isolate KREDT. A member of the Subcommittee on the Taxonomy of Enterobacteriaceae for the International Committee on Systematics of Prokaryotes conducted a re-examination of S. marcescens KREDT and failed to detect its endospore-forming capability, thereby questioning the validity of S. marcescenssubsp. sakuensis as a separate subspecies. Nevertheless, the taxonomic allocation of S. marcescenssubsp. sakuensis has been followed till date. To obtain clarity for taxonomic allocation based on genome-based analysis, we sequenced the genome of type strain S. marcescenssubsp. sakuensis KREDT=DSM 17174T and carried out the analyses recommended to define the subspecies. As a result, DSM 17174T does not satisfy the genomic criteria for defining a subspecies: i.e. does not form a distinguishable clade by overall genomic related indexing and phylogenomic treeing. Also, there is currently no other rationale for separate recognition of this species. We propose the removal of the S. marcescenssubsp. sakuensis designation to avoid further confusion in the literature.