title: Differential expression of sulfur assimilation pathway genes in Acidithiobacillus ferrooxidans under Cd²⁺ stress: evidence from transcriptional, enzymatic, and metabolic profiles.
abstract: Acidithiobacillus ferrooxidans is a heavy metal-tolerant acidophilic chemolithotroph found in acidic mine effluent and is used commercially in the bioleaching of sulfide ores. In this work, we investigated the interplay between divalent cadmium (Cd(2+)) resistance and expression of genes involved in the sulfur assimilation pathway (SAP). We also investigated the response of the thiol-containing metal-chelating metabolites, cysteine and glutathione(GSH), to increasing Cd(2+) concentrations. During growth in the presence of 30 mM Cd(2+), the concentrations of mRNA for 5 genes in the SAP pathway increased more than fourfold: these encode ATP sulfurylase (ATPS), adenosine 5'-phosphosulfate (APS) reductase, sulfite reductase (SiR), serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL). Increased transcription was also reflected in increased enzyme activities: those of SAT and adenosylphosphosulfate reductase (APR) reached a peak of 26- and 15.8-fold, respectively, compared to the control culture in the presence of 15 mM Cd(2+). In contrast, the activity of OAS-TL, which is responsible for the biosynthesis of cysteine, was diminished. At the metabolite level, the intracellular cysteine and GSH contents nearly doubled. These results suggested that Cd(2+) induced transcription of SAP genes, while directly inhibiting the activities of some enzymes (e.g., OAS-TL). Overall, these results are consistent with a detoxification/resistance mechanism involving enhanced sulfur uptake and sequestration of Cd(2+) by cysteine and glutathione.
authors.affiliation: Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou, 014010, China, zhengchunli1979@163.com.
authors.forename: Chunli
authors.initials: C
authors.lastname: Zheng
authors.forename: Minjie
authors.initials: M
authors.lastname: Chen
authors.forename: Zhanlong
authors.initials: Z
authors.lastname: Tao
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Xue Feng
authors.initials: XF
authors.lastname: Zhang
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Wang
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D042763:Acidithiobacillus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002104:Cadmium / Q000633:toxicity*; D003545:Cysteine / Q000096:biosynthesis; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D055442:Metabolome; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological; D013430:Sulfate Adenylyltransferase / Q000235:genetics / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D012333:RNA, Messenger; D002104:Cadmium; D013455:Sulfur; D050862:Oxidoreductases Acting on Sulfur Group Donors; D013430:Sulfate Adenylyltransferase; D003545:Cysteine