Research Info

Metallothionein and metal‐binding peptides are small cysteine‐rich proteins produced by different organisms in stress conditions. In this study, the metal‐binding peptide was detected in extracellular proteins of a new Bacillus velezensis strain, isolated from metal contaminated soil, and grown on the lead‐enriched medium, for the first time. The presence of sulfide peptide was assayed by two simple tests (lead sulfide and Ellman's reagent test) for preliminary, and subsequently confirmed using polyacrylamide gel electrophoresis at media with different lead concentrations that the lowmolecular‐ weight protein fragments (≈10 kDa) were observed while none were detected in the medium containing sodium chloride or calcium salt. The amino acids of the observed fragments were analyzed by matrixassisted laser desorption ionization time‐of‐flight tandem mass spectrometry (MALDI‐TOF MS/MS). Also, the metal adsorption was confirmed using sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDSPAGE) by staining with chromium solution. The results showed that the putative sulfide peptide is metallothionein, which is induced in stress conditions. It was interesting that in all SDS profiles, one protein fragment (≈18 kDa) was inhibited in lead‐enriched media. The data from MALDITOF MS/MS analysis showed that this fraction was a chitin‐binding protein whose production was regulated by metal contamination. It is anticipated that these two proteins regulate the toxicity of lead.