Sugar supplementation enhances biofilm formation and extracellular polysaccharides production in Sulfobacillus acidophilus.

Sulfobacillus is an acidophilic bacterial genus that plays a key role in bioleaching of metal sulfides at moderately thermophilic temperatures (45-55 °C), owing to its mixotrophic metabolism and capacity to form biofilms. Biofilm development depends on an extracellular polymeric substances (EPS) matrix, which is largely composed of polysaccharides. However, the composition and function of polysaccharides in sulfobacilli remain poorly characterized. A genome-wide survey identified a diverse repertoire of putative sugar uptake transporters, belonging to three distinct families. We demonstrate that supplementation with glucose, fructose, xylose or sucrose increases biofilm formation and extracellular polysaccharides production in Sulfobacillus acidophilus DSM 10332ᵀ. Enhanced biofilm formation was quantified using large-scale, in-depth image analysis. Fluorescent lectin binding analysis revealed a concomitant increase in extracellular polysaccharides abundance, while HPLC-UV-ESI-MS confirmed a quantitative rise in secreted polysaccharides under sugar-supplemented conditions. Detailed compositional analysis showed that the extracellular polysaccharides produced by S. acidophilus T are predominantly composed of glucose and mannose residues. Overall, our findings indicate that sugar supplementation stimulates biofilm development in S. acidophilus, likely by enhancing extracellular polysaccharides biosynthesis. This study provides the first detailed compositional characterization of S. acidophilus T extracellular polysaccharides and establishes Sulfobacillus as a promising model for investigating sugar uptake and carbon cycling in bioleaching systems, as members of this genus can also grow without the supplementation of sugars.