Production of a cellulose-aminating polysaccharide from a filamentous sulfur-oxidizing bacterium, Thiothrix nivea, grown lithotrophically or mixotrophically.

Aims: Glucosaminoglucan (β-1,4-linked glucose and glucosamine) produced by a mixotrophic sulfur-oxidizing bacterium, Thiothrix nivea, is a useful cellulose-aminating agent. Lithotrophic and mixotrophic glucosaminoglucan production were examined using fed-batch techniques.

Methods and results: A jar fermenter was used for the fed-batch cultivation. Glucosaminoglucan was extracted from T. nivea using diluted HCl. Lithotrophic growth was detected by feeding with Na2S as the energy source, and 12 mg L-culture-1 of glucosaminoglucan was obtained. In contrast, no growth was observed with Na2S2O3. Similarly, mixotrophic growth in the presence of acetic acid was promoted by Na2S, whereas Na2S2O3 had no effect. When acetic acid and Na2S were added, 470 mg L-culture-1 of glucosaminoglucan was obtained.

Conclusions: T. nivea was cultured and glucosaminoglucan was produced lithotrophically using Na2S for feeding. Na2S is also indispensable for mixotrophic growth and glucosaminoglucan production, indicating that sulfide oxidation pathways control the TCA cycle. The involvement of the SOX pathway (for thiosulfate oxidation) in the activation of energy metabolism is doubtful because neither lithotrophic nor mixotrophic growth was promoted by Na2S2O3. Based on these results, we assumed that T. nivea is facultatively mixotrophic (lithotrophic growth is possible in addition to organotrophic growth in the presence of sulfide (Na2S)), rather than obligately mixotrophic.