Proteomic and molecular investigations revealed that Acidithiobacillus caldus adopts multiple strategies for adaptation to NaCl stress.

Acidithiobacillus caldus plays an important role in commercial bioleaching. To understand how NaCl stress adaptation occurs in A. caldus, we grew A. caldus strain SM-1 in media containing high NaCl concentrations. SM-1 grew at concentrations of up to 1.0-mol L NaCl, but growth was severely inhibited at higher concentrations. Proteomic analysis showed that SM-1 used multiple strategies to respond to NaCl stress. In addition to several heat-shock proteins, enzymes involved in proline biosynthesis increased under NaCl stress. In addition, two DNA-binding proteins and a third protein of unknown function (Atc_1291), which was subsequently identified as a putative single-stranded DNA-binding protein, were up-regulated in the presence of NaCl stress. These DNA-binding proteins might play a role in response to osmotic stress. Atc_1291 was cloned and expressed in Escherichia coli. Surprisingly, we found that E. coli BL21/pET28a-atc_1291 grew to higher cell densities than E. coli BL21/pET28a, regardless of NaCl stress. Homologs to Atc_1291 were identified in several groups of Proteobacteria. The role of Atc_1291 in enhancing cell growth needs further investigation. [ABSTRACT FROM AUTHOR]