Bioleaching in brackish waters—effect of chloride ions on the acidophile population and proteomes of model species

Abstract

High concentrations of chloride ions inhibit the growth of acidophilic microorganisms used in biomining, a problem particularly relevant to Western Australian and Chilean biomining operations. Despite this, little is known about the mechanisms acidophiles adopt in order to tolerate high chloride ion concentrations. This study aimed to investigate the impact of increasing concentrations of chloride ions on the population dynamics of a mixed culture during pyrite bioleaching and apply proteomics to elucidate how two species from this mixed culture alter their proteomes under chloride stress. A mixture consisting of well-known biomining microorganisms and an enrichment culture obtained from an acidic saline drain were tested for their ability to bioleach pyrite in the presence of 0, 3.5, 7, and 20 g L(-1) NaCl. Microorganisms from the enrichment culture were found to out-compete the known biomining microorganisms, independent of the chloride ion concentration. The proteomes of the Gram-positive acidophile Acidimicrobium ferrooxidans and the Gram-negative acidophile Acidithiobacillus caldus grown in the presence or absence of chloride ions were investigated. Analysis of differential expression showed that acidophilic microorganisms adopted several changes in their proteomes in the presence of chloride ions, suggesting the following strategies to combat the NaCl stress: adaptation of the cell membrane, the accumulation of amino acids possibly as a form of osmoprotectant, and the expression of a YceI family protein involved in acid and osmotic-related stress.

Microbial behaviour under conditions relevant to heap leaching: Studies using the sulfur-oxidising, moderate thermophile Acidithiobacillus caldus

“…In another study, At. caldus cultures grown on elemental sulfur with 7 g L −1 NaCl for two weeks had planktonic cell densities 72% of those in cultures grown without added NaCl (Zammit et al, 2012), an estimate somewhat higher than the 42% obtained for the 5 g L −1 test in the present study. No other data on the sodium chloride tolerance of At.…”

Biotechnological Exploitation of Actinobacterial Members

“…This capability was also reported from alkaliphilic, heterotrophic microorganisms (Willscher and Bosecker 2001 ), and more recently from some halotolerant actinobacteria such as genera Nocardiopsis (Schippers et al 2002 ). The growth of acidophilic microorganisms are chloride-dependent and are inhibited in presence of high concentration of this ion (Zammit et al 2012 ), thus the halophilic and halotolerant actinobacteria are of special interest due to their ability to thrive in high concentration of NaCl allowing to take advantage of seawater for prospective biomining techniques in drought affected environments. …”

Ferrous bio-oxidation byAcidithiobacillus ferrooxidansin hydrochloric acid pickling waste liquor

“…Chloride ion inhibition was observed when sodium chloride was added. Zammit et al also found that elevated chloride levels in leach solutions were inhibitory to iron-and sulfur-oxidizing microorganisms [17]. Iron (II) oxidation rate slowed down obviously while the time needed to reach the .…”