Genomic Evolution of Siccibacter colletis: Comparative Analysis and First Clinical Isolate Report

The genus Siccibacter consists primarily of environmental bacteria, with strains of Siccibacter colletis previously isolated only from plant materials and related environments. This study aims to characterize the first clinical isolate of S. colletis and explore its genomic evolution and clinical relevance. Strain S25242 was isolated from the urine of a 64-year-old male with a severe urinary tract infection. The genome of S25242 is 4.19 Mb, containing 4012 coding sequences, 73 tRNAs, 10 rRNAs, and 38 snRNAs. Phylogenetic and phylogenomic analyses indicated that strain S25242 is closely related to S. colletis type strain 1383^T. The strain shared >70% of digital DNA-DNA hybridization (dDDH) values and >96% of average nucleotide identity (ANI) values with the type strain of S. colletis 1383^T, thereby confirming its taxonomic status. The isolate was susceptible to all 11 tested antimicrobials. Comparative genomics identified 1942 S. colletis-specific genes (including multidrug efflux systems) and 13 unique genes in S25242 related to transposition and DNA integration. This study reports the first clinical isolate of S. colletis, providing evidence that genomic plasticity facilitates its transition from an environmental inhabitant to an opportunistic pathogen. The findings highlight the need for enhanced clinical surveillance of the Siccibacter genus and offer insights into its genomic evolution and clinical adaptation.