Deciphering hypersaline tolerance mechanism of the pyridine-degrading strain Rhodococcus sp. PD10

Pyridine is a common pollutant in the hypersaline wastewater from chemical and pharmaceutical industries, posing environmental and health risks. A Rhodococcus sp. strain capable of effectively degrading pyridine was isolated and enhanced to tolerate 10 % NaCl through adaptive laboratory evolution, resulting in Rhodococcus sp. PD10. Comparative genome analysis with qRT-PCR experimental verification suggested that the inhibition of cAMP degradation, accompanied with enhanced salt-tolerance of protein and increased energy production, likely contributed to strain PD10’s ability to survive in high salinity. Notably, an unusual metabolite, 7-methylguanine, was newly discovered to accumulate under abiotic conditions using untargeted metabolomics, and it was experimentally shown to favor cell growth in hypersaline environments, alongside compatible solutes like ectoine and the rare compound N δ -acetylornithine. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis further indicated that preserving cell membrane stability and fluidity is crucial for the survival of the strain under high salt stress. This study systematically uncovered the salt-tolerance mechanism of Rhodococcus sp. strain PD10, demonstrating its promising industrial applications. • A pyridine-degrading Rhodococcus sp. strain was evolved to tolerate 10 % NaCl. • Inhibition of cAMP degradation enhances salt stress tolerance of the strain under high salinity. • The presence of 7-methylguanine was found to promote cell growth under hypersaline conditions. • Maintaining cell membrane stability and fluidity is critical for survival under high salinity.