Transcriptional response of Pseudomonas chenduensis strain MBR to cadmium toxicity

Cadmium (Cd) contamination has resulted in serious environmental pollution and threatens human health and ecosystems. Our recent studies have demonstrated that Pseudomonas chenduensis strain MBR can decrease Cd bio-availability and reduce Cd accumulation in rice; however, the transcriptional mechanisms underlying the bacterial response during and particularly after Cd bioremediation are still unclear. In this study, we used RNA-Seq to investigate the transcriptional profiles of strain MBR during and after Cd bioremediation. During Cd bioremediation, MBR removed all Cd²⁺ ions in solution within 24 h, accompanied by 564 upregulated and 363 downregulated expressed genes compared with that of the control (without Cd supplementation). Specifically, under Cd stress, the upregulation of czc (czcA, czcB, and czcC) and mer (merA, merT, merC, and merP) genes enabled Cd efflux from the cytoplasm and conferred resistance of MBR to Cd toxicity. The upregulation of genes (algK, algX, and alg44) related to biofilm formation enabled Cd absorption and contributed to Cd bioremediation. After Cd bioremediation, MBR was transferred to non-Cd medium, and the genes related to histidine metabolism and flagellar assembly still showed similar expression patterns as those during bioremediation (defined as Cd legacy effects). However, the genes involved in Cd resistance and bioremediation were not influenced by Cd legacy effects. This study provides new and thorough insights into the molecular mechanisms underlying Cd bioremediation by a functional microbe. KEY POINTS: • The upregulation of czc and mer genes is responsible for MBR resistance to Cd. • The upregulation of genes related to biofilm formation contributes to Cd bioremediation. • Cd effects on genes involved in histidine metabolism and flagellar assembly are long-lasting.