New Features of Acidophilic Bacteria of the Genus Sulfobacillus: Polysaccharide Biosynthesis and Degradation Pathways

Abstract

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.