Synchrotron radiation based STXM analysis and micro-XRF mapping of differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on Fe2+ and S0

The differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on substrates Fe2+ and S0 was investigated by using synchrotron radiation based scanning transmission X-ray microscopy (STXM) imaging and microbeam X-ray fluorescence (μ-XRF) mapping. The extracellular thiol groups (SH) were first alkylated by iodoacetic acid forming Protein-SCH2COOH and then the P-SCH2COOH was marked by calcium ions forming P-SCH2COOCa. The STXM imaging and μ-XRF mapping of SH were based on analysis of SCH2COO-bonded Ca2+. The results indicated that the thiol group content of A. ferrooxidans grown on S0 is 3.88 times to that on Fe2+. Combined with selective labeling of SH by Ca2+, the STXM imaging and μ-XRF mapping provided an in situ and rapid analysis of differential expression of extracellular thiol groups. •STXM imaging and m-XRF mapping were firstly used for thiol group analysis.•The membrane thiol groups were selectively labeled with Ca2+.•STXM image provided an in situ evaluation of extracellular thiol groups.•Micro-XRF mapping was rapid to determine the differential expression of thiol groups.•The -SH content of A. ferrooxidans grown on S0 was 3.88 times more to that on Fe2+.