Abstract:

Objective: This study investigated the tolerance and removal ability of the plant growth-promoting bacterium Burkholderia contaminans JLS17 to Cd²⁺ and its metabolic response under Cd²⁺ stress, so as to provide a basic theoretical basis for the application of the strain in soil Cd pollution remediation, and to provide data support for exploring molecules and metabolic pathways with anti-cadmium function and the elucidation of the microbial Cd tolerance mechanism. Method: The tolerance of the strain to Cd²⁺ was evaluated by measuring the OD₆₀₀ values of cultures with different Cd²⁺ concentrations, the removal efficiency of Cd²⁺ from LB medium was determined using inductively coupled plasma mass spectrometry (ICP-MS), and the differential metabolites and metabolic pathways of the strain under Cd²⁺ stress were analyzed by untargeted metabolomics (LC-MS). Result: 1) There was a significant inhibition of Cd²⁺ stress on the growth rate and biomass (OD₆₀₀) of strain JLS17 with different levels of Cd²⁺ stress (50 mg·L^?1?800 mg·L^?1), and the inhibition increased with the increasing Cd²⁺ concentration. 2) The removal quantity of Cd²⁺ from LB medium by strain JLS17 increased with the increasing Cd²⁺ concentration (10?100 mg·L^?1) and the highest removal quantity was 55.90 mg·L^?1. However, the removal rate was less affected by Cd²⁺ concentration and maintained at 41.9%?66.0%. 3) The results of LC-MS analysis showed that strain JLS17 had the same expression trend, with 147 differential metabolites, under 50 mg·L^?1 Cd²⁺ treatment and 300 mg·L^?1 Cd²⁺ treatment, of which 92 metabolites were up-regulated and 55 metabolites were down-regulated, mainly covering amino acids and their derivatives, nucleotides and their derivatives, lipids, organic acids and their derivatives, terpenoids, ketones, alkaloids, etc. The results of KEGG enrichment analysis showed that strain JLS17 significantly enriched common metabolic pathways after 50 mg·L^?1 Cd²⁺ treatment and 300 mg·L^?1 Cd²⁺ treatment, including pyrimidine metabolism, aminobenzoate degradation, cysteine and methionine metabolism, tryptophan metabolism, β-alanine metabolism, folate biosynthesis and pentose phosphate pathway, among which pyrimidine metabolism, tryptophan metabolism and pentose phosphate pathway were down-regulated in common and folate biosynthesis was up-regulated in common. Conclusion: 1) The strain JLS17 has excellent adaptability to Cd²⁺ stress and can remove Cd²⁺ from LB medium effectively, showing good potential for application in remediation of Cd pollution. 2) The strain JLS17 can affect metabolic pathways in vivo through changes in the content of amino acids and their derivatives, nucleotides and their derivatives, lipids and other metabolites under Cd²⁺ stress, among which tryptophan metabolism, β-alanine metabolism, cysteine and methionine metabolism, pyrimidine metabolism, pentose phosphate pathway, folate biosynthesis are closely related to the Cd²⁺ tolerance of strain JLS17.

Key words: cadmium pollution, plant growth-promoting bacterium, tolerance mechanism, heavy metal adsorption, metabolome