High concentrations of chloride ions inhibit the growth of acidophilic iron and sulfur oxidizing microorganisms used in biomining, a problem particularly relevant to Western Australian and Chilean biomining operations. This growth inhibition is due to the chloride ion disrupting homeostatic mechanisms resulting in acidification of the cytoplasm. Acidihalobacter prosperus is an acidophile that has been shown to oxidize iron at levels of NaCl as high as 50 g.L-1. However, little is known about the mechanisms this microorganism adopts in order to tolerate such high chloride ion concentrations. This study applied proteomics to elucidate how A. prosperus alters its proteome under high chloride concentrations.
A. prosperus (DSM 5130 T) was grown in the presence of sub-optimal (3.8 g.L-1) and optimal (30 g.L-1) NaCl concentrations. Total soluble proteins produced by cells were compared using 2D LC mass spectrometry with iTRAQ. Spectral data were analysed against a protein sequence database for the whole genome using ProteinPilot™ 4.5 Software.
Analysis of differential expression showed that A. prosperus adopted several changes in its proteome in response to increased NaCl levels. These included maintenance of cell wall and outer membrane function and increased abundance of proteins involved in iron and sulfur oxidation. However a reduction in proteins involved in carbon metabolism was noted. A range of osmotic responses were seen including synthesis of compatible solutes and transport proteins. The two component signal transduction osmolarity response regulator was uniquely expressed at high salt conditions. Gaining an understanding of the range of mechanisms that acidophilic iron oxidizing microorganisms may use to help the cell function in the presence of elevated concentrations of chloride can be applied to the development of saline biomining operations or improve alterative processes.
Acknowledgements: Fondecyt 1130683. This study was funded by a Bioplatforms Australia Omics grant.