Genomic insights into abiotic stress tolerance in polar lichen-associated Sphingomonas sp. PAMC26617 and Sphingomonas...

In this study, Sphingomonas sp. PAMC26617 and Sphingomonas sp. PAMC26621 isolated from rocks of an Arctic lichen, Umbillicaria sp. and Cetraria sp. respectively, were evaluated for their tolerance to abiotic stress of heavy metal(loid)s (HMMs), salt, and osmotic (drought-like) stress at two different temperatures. HMMs resistance protein (CzcC, CzcD, CopB, CopC, CopD, ArsH, and CorC), and osmoprotectant enzymes such as gamma-glutamyl phosphate reductase (ProA), glutamate 5-kinase (ProB), and pyrroline-5-carboxylate reductase (ProC) were identified in both strains during genome analysis. Heavy metal (HM) resistance protein (CorA) was only identified in Sphingomonas sp. PAMC26621. In addition, both strains showed tolerance to CuSO₄·5H₂O (0.1 mM at 15 °C and 0.25 mM at 25 °C), CoCl₂·6H₂O (0.25 mM at 15 °C and 0.1 mM at 25 °C), ZnSO₄·7H₂O (0.1 mM at 15 °C and 25 °C) and Na₂HAsO₄·7H₂O (10 mM at 15 °C and 25 °C), except for Cd(NO₃)₂·4H₂O. Sphingomonas sp. PAMC26617 showed 0.05 mM Cd(NO₃)₂·4H₂O at 15 °C and 0.01 mM at 25 °C and Sphingomonas sp. PAMC26621 showed 0.01 mM Cd(NO₃)₂·4H₂O at 15 °C and 25 °C, respectively. Furthermore, both strains showed tolerance up to 100 mM NaCl and 100 mM D-mannitol at both temperatures. This study is very informative and helpful in understanding the diversity and adaptability of lichen-associated bacteria in harsh environments.