title: Multiple Osmotic Stress Responses inAcidihalobacter prosperusResult in Tolerance to Chloride Ions.
abstract: Extremely acidophilic microorganisms (pH optima for growth of ≤3) are utilized for the extraction of metals from sulfide minerals in the industrial biotechnology of "biomining." A long term goal for biomining has been development of microbial consortia able to withstand increased chloride concentrations for use in regions where freshwater is scarce. However, when challenged by elevated salt, acidophiles experience both osmotic stress and an acidification of the cytoplasm due to a collapse of the inside positive membrane potential, leading to an influx of protons. In this study, we tested the ability of the halotolerant acidophileAcidihalobacter prosperusto grow and catalyze sulfide mineral dissolution in elevated concentrations of salt and identified chloride tolerance mechanisms inAc. prosperusas well as the chloride susceptible species,Acidithiobacillus ferrooxidans.Ac. prosperushad optimum iron oxidation at 20 g L-1NaCl whileAt. ferrooxidansiron oxidation was inhibited in the presence of 6 g L-1NaCl. The tolerance to chloride inAc. prosperuswas consistent with electron microscopy, determination of cell viability, and bioleaching capability. TheAc. prosperusproteomic response to elevated chloride concentrations included the production of osmotic stress regulators that potentially induced production of the compatible solute, ectoine uptake protein, and increased iron oxidation resulting in heightened electron flow to drive proton export by the F0F1ATPase. In contrast,At. ferrooxidansresponded to low levels of Cl-with a generalized stress response, decreased iron oxidation, and an increase in central carbon metabolism. One potential adaptation to high chloride in theAc. prosperusRus protein involved in ferrous iron oxidation was an increase in the negativity of the surface potential of Rus Form I (and Form II) that could help explain how it can be active under elevated chloride concentrations. These data have been used to create a model of chloride tolerance in the salt tolerant and susceptible speciesAc. prosperusandAt. ferrooxidans, respectively.
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University Kalmar, Sweden.
authors.forename: Mark
authors.initials: M
authors.lastname: Dopson
authors.affiliation: Facultad de Ciencias Biologicas, Universidad Andres BelloSantiago, Chile; Center for Bioinformatics and Genome Biology, Fundacion Ciencia y VidaSantiago, Chile.
authors.forename: David S
authors.initials: DS
authors.lastname: Holmes
authors.affiliation: Facultad de Ciencias Biologicas, Universidad Andres BelloSantiago, Chile; Center for Bioinformatics and Genome Biology, Fundacion Ciencia y VidaSantiago, Chile.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Lazcano
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: McCredden
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Bryan
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Kieran T
authors.initials: KT
authors.lastname: Mulroney
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Robert
authors.initials: R
authors.lastname: Steuart
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Connie
authors.initials: C
authors.lastname: Jackaman
authors.affiliation: School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University Perth, WA, Australia.
authors.forename: Elizabeth L J
authors.initials: EL
authors.lastname: Watkin
keywords: acidophile; bioleaching; biomining; chalcopyrite; environmental stress; proteomics; pyrite; salt