Diversity and Ecophysiology of New Isolates of Extremely Acidophilic CS 2 -Converting Acidithiobacillus Strains

Abstract

Biofiltration of industrial carbon disulfide (CS2)-contaminated waste air streams results in the acidification of biofilters and therefore reduced performance, high water use, and increased costs. To address these issues, we isolated 16 extremely acidophilic CS2-converting Acidithiobacillus thiooxidans strains that tolerated up to 6% (vol/vol) sulfuric acid. The ecophysiological properties of five selected strains (2Bp, Sts 4-3, S1p, G8, and BBW1) were compared. These five strains had pH optima between 1 (2Bp) and 2 (S1p). Their affinities for CS2 ranged between 80 (G8) and 130 (2Bp) μM. Strains S1p, G8, and BBW1 had more hydrophobic cell surfaces and produced less extracellular polymeric substance than did strains 2Bp and Sts 4-3. All five strains converted about 80% of the S added as CS2 to S(0) when CS2 was supplied in excess. The rate of S(0) consumption varied between 7 (Sts 4-3) and 63 (S1p) nmol O2 min(-1) ml culture(-1). Low S(0) consumption rates correlated partly with low levels of cell attachment to externally produced S(0) globules. During chemostat growth, the relative amount of CS2 hydrolase in the cell increased with decreasing growth rates. This resulted in more S(0) accumulation during CS2 overloads at low growth rates. Intermittent interruptions of the CS2 supply affected all five strains. Strains S1p, G8, and BBW1 recovered from 24 h of starvation within 4 h, and strains 2Bp and Sts 4-3 recovered within 24 h after CS2 was resupplied. We recommend the use of mixtures of Acidithiobacillus strains in industrial biofilters.