The transcriptomic response of Staphylococcus equorum KS1030 to Lincomycin stress reveals transporters associated with horizontal gene transfer

The spread of antibiotic resistance through horizontal gene transfer (HGT) in food-associated bacteria represents an emerging public health concern. Staphylococcus equorum strain KS1030, isolated from a high-salt fermented food, carries plasmids encoding the lincomycin resistance gene lnuA and the relaxase gene rlx, both of which contribute to resistance dissemination. Previous studies have shown that strain KS1030 can transfer the lnuA gene both within and across subspecies when exposed to lincomycin. To investigate the transcriptional basis of this phenomenon, we performed RNA sequencing (RNA-Seq) to analyze the global gene expression profile of KS1030 under lincomycin stress (30 mg/L). Transcriptome analysis revealed more differentially expressed genes (DEGs) at 2 h than at 4 h, with enriched categories including amino acid transport and metabolism (22.9%), transcription (19.3%), and inorganic ion transport and metabolism (14.7%). Genes involved in ornithine, Fe³⁺, siderophore, and tryptophan metabolism, as well as stress regulators such as sigB, dcuSR, and helix-turn-helix transcriptional regulators, were strongly induced. Genome analysis further identified the competence (Com) operon and DNA translocase (ftsK) as potential transport systems, with comGC classified as a DEG. To capture short-term dynamics not resolved by RNA-Seq, quantitative real-time PCR was performed at 30-min intervals. Several genes, including comC, comEC, comFA, and ftsK, peaked at 1.5 h, while lnuA and rlx peaked at 1 h. Although the roles of the Com and FtsK systems in HGT remain unresolved, their induction under lincomycin stress suggests a potential contribution to plasmid transfer, offering new insight into the adaptive and gene transfer responses of S. equorum. However, as this study relies solely on transcriptional data from a single strain and antibiotic condition, functional validation-such as targeted gene disruption-will be required to confirm the involvement of these candidate HGT-related genes.