Comparative genomic and physiological characterization of a lichen-associated Streptacidiphilus strain from Antarctica.

Streptacidiphilus sp. PAMC 29251 represents the first member of its genus isolated from an Antarctic fruticose lichen Sphaerophorus globosus. To elucidate its ecological, metabolic, and biosynthetic features, we performed comparative genomic analyses in combination with physiological assays. PAMC 29251 exhibited distinct ecophysiological features compared with previously described Streptacidiphilus species, including the ability to grow at 4°C and across a broad alkaline range (pH 6.5-10.0). Genome sequencing revealed a 10.11 Mb linear chromosome containing 9,547 coding sequences, including 31 biosynthetic gene clusters (BGCs)-one of the richest repertoires within the genus. Several BGCs, including those putatively encoding lomofungin, maduralactomycin, and thiolactomycin, were detected only in PAMC 29251 among 14 Streptacidiphilus genomes investigated in this study. Consistent with these predictions, both cell and supernatant extracts showed antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans. Although PAMC 29251 lacked nitrogen fixation and phosphate solubilization, it possessed the capacity to hydrolyze multiple macromolecules and encoded diverse proteases and carbohydrate-degrading enzymes, suggesting a potential role in organic matter turnover within the lichen thallus. These results indicate that PAMC 29251 maintains the core genomic architecture of the genus Streptacidiphilus while exhibiting differentiated physiological traits and biosynthetic features, which may be relevant to its functional characteristics in lichen-associated environments.