High lead-tolerant mutant Bacillus tropicus AT31-1 from rhizosphere soil of Pu-erh and its remediation mechanism.

In this study, we successfully generated the mutant strain Bacillus tropicus AT31-1 from AT31 through atmospheric room-temperature plasma mutagenesis. This mutant strain AT31-1 demonstrated an impressive 48.6 % removal efficiency in 400 mg/L lead medium. Comparative genomic analysis showed that the mutant strain AT31-1 had three mutation sites, which affect the efflux RND transporter permease subunit, the response regulator transcription factor, and a gene with unknown function. The transcriptional analysis showed a notable upregulation in the expression of 283 genes in AT31-1 as lead concentrations increased from 0 to 200 mg/L and then to 400 mg/L, which include zinc-transporting ATPase, ferrous iron transport protein B, NADH dehydrogenase, and others. The Gene ontology function of the peptide metabolic process, along with the KEGG pathway of carbon metabolism were identified as closely linked to the extreme lead tolerance of AT31-1. This study presents novel insights into the lead tolerance mechanisms of bacteria.