Search Results (3)

Bacteria of the genus Sulfobacillus are predominant members of acidophilic microbial communities involved in the bioprocessing of sulfide raw materials. Genomic analysis of different Sulfobacillus species revealed a starch/glycogen GlgE-dependent biosynthesis pathway of α-glucans from trehalose in S. thermotolerans and S. thermosulfidooxidans. The key enzyme of this pathway, a fused maltose-trehalose/α-amylase protein, was not encoded in the genomes of other Sulfobacillus bacteria. At the same time, the presence of all genes encoding enzymes for α-glucan decomposition allowed the prediction of polysaccharide degradation pathways in these two species. Despite the optimum mixotrophic type of metabolism, a gradual adaptation of Sulfobacillus bacteria to polysaccharides resulted in their active organotrophic growth. Moreover, the enzyme assay determined the activities of the extracellular enzymes involved in glycogen and starch degradation. In acidophilic communities of natural and industrial habitats, an essential function of polysaccharides in the composition of extracellular polymeric substances of slime matrices is to promote the attachment of the microbial cells to solid surfaces, such as mineral particles. Polysaccharides can also be storage compounds used for energy and carbon metabolism under specific environmental conditions. Understanding the metabolic capabilities of Sulfobacillus bacteria in consuming and synthesizing α-glucans, which are provided in this study, is of fundamental importance in understanding acidophilic microbial communities and their application in practice. Full article

Biooxidation of gold-bearing arsenopyrite concentrates, using acidophilic microbial communities, is among the largest commercial biohydrometallurgical processes. However, molecular mechanisms of microbial responses to sulfide raw materials have not been widely studied. The goal of this research was to gain insight into the defense strategies of the acidophilic bacterium Sulfobacillus thermotolerans, which dominates microbial communities functioning in industrial biooxidation processes at >35 °C, against the toxic effect of the high-arsenic gold-bearing sulfide concentrate. In addition to extreme metal resistance, this acidophile proved to be one of the most As-tolerant microorganisms. Comparative proteomic analysis indicated that 30 out of 33 differentially expressed proteins were upregulated in response to the ore concentrate, while the synthesis level of the functional proteins required for cell survival was not negatively affected. Despite a high level of cellular metal(loid) accumulation, no specific metal(loid)-resistant systems were regulated. Instead, several proteins involved in the metabolic pathways and stress response, including MBL fold metallo-hydrolase, sulfide:quinone oxidoreductase, and GroEL chaperonin, may play crucial roles in resistance to the sulfide ore concentrate and arsenic, in particular. This study provides the first data on the microbial responses to sulfide ore concentrates and advances our understanding of defense mechanisms against toxic compounds in acidophiles. Full article

A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40 °C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation. Full article