Abstract
Acidihalobacter aeolianus is an acidophilic, halo-tolerant organism isolated from a marine environment near a hydrothermal vent, an ecosystem whereby levels of salinity and total dissolved salts are constantly fluctuating creating ongoing cellular stresses. In order to survive these continuing changes, the synthesis of compatible solutes—also known as organic osmolytes—is suspected to occur, aiding in minimising the overall impact of environmental instability. Previous studies on A. aeolianus identified genes necessary for the accumulation of proline, betaine and ectoine, which are known to act as compatible solutes in other halophilic species. In this study, the impact of increasing the osmotic stress as well as the toxic ion effect was investigated by subjecting A. aeolianus to concentrations of NaCl and MgSO4 up to 1.27 M. Exposure to high concentrations of Cl− resulted in the increase of ectC expression in log-phase cells with a corresponding accumulation of ectoine at stationary phase. Osmotic stress via MgSO4 exposure did not trigger the same up-regulation of ectC or accumulation of ectoine, indicating the transcriptionally regulated response against osmotic stress was induced by chloride toxicity. These findings have highlighted how the adaptive properties of halo-tolerant organisms in acidic environments are likely to differ and are dependent on the initial stressor.
Highlights
IntroductionThe microorganisms favoured in biomining operations oxidise iron and sulphur at low pH, resulting in the solubilisation of sulphide minerals
Academic Editors: Tsing Bohu, The exploitation of microorganisms and their capabilities for biotechnological process is widespread in many industries and underlies the foundation of biomining operations.The microorganisms favoured in biomining operations oxidise iron and sulphur at low pH, resulting in the solubilisation of sulphide minerals
When studying the impact of osmotic stress on A. aeolianus, our results showed that exposure to increasing concentrations of MgSO4 hindered iron oxidation rates, no significant increase in ectC transcription correlated with this finding, as the relative expression of ectC in low MgSO4 was 0.89 and at high MgSO4, only 0.91
Summary
The microorganisms favoured in biomining operations oxidise iron and sulphur at low pH, resulting in the solubilisation of sulphide minerals. These acidophiles, whilst very good at mineral solubilisation, are typically sensitive to salinity [1,2], which can restrict biomining operations in areas where fresh water is limited. The low tolerance to salinity is attributed to the disruption of the chemiosmotic barrier by chloride ions moving into the cytoplasm. Chloride ions can pass this barrier and accumulate, neutralizing the transmembrane potential thereby limiting the proton motive force and the accompanying cytoplasmic acidification resulting in cell death [5]
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