Acidiphilium symbioticum sp.nov., an acidophilic heterotrophic bacterium from Thiobacillus ferrooxidans cultures isolated from Indian mines

Abstract

Two cultures of Thiobacillus ferrooxidans enriched from Indian mine samples and grown autotrophically on FeSO4 – basal salts medium for periods ranging from several months to years contained acidophilic, heterotrophic bacterial contaminants. The heterotrophs (strains KM2 and H8) were isolated by selective growth in a mineral salts – glucose – yeast extract medium of pH 3 and were purified as single colonies on an agarose medium. Mannose, galactose, sucrose, lactose, citrate, mannitol, and glycerol supported the growth of these strains in the presence of yeast extract. The heterotrophs grew poorly or failed to grow in media without yeast extract. They could not grow autotrophically with Fe2+, or with sulfur and its oxidizable derivatives, as the sole source of energy. Although they exhibited many characteristics of the genus Acidiphilium, they differed from Acidiphilium cryptum and other species of this genus in some physiological properties, notably in their ability to grow at higher glucose (5%, w/v) and Mn2+ (20 mM) concentrations. The G+C mol% contents (58.8 and 60.2) of strains KM2 and H8, respectively, determined from melting temperature (Tm) values were close to that of A. cryptum (62.7%). Strains KM2 and H8 showed 70–80% DNA homology with each other and about 60% with A. cryptum. All of the strains, including A. cryptum, responded similarly to several metal ions and antibiotics. SDS–PAGE of whole-cell proteins exhibited striking similarity between these two isolated strains, which were unlike that of A. cryptum. The strains were also agglutinated with a few common lectins and differed strongly from A. cryptum in respect to wheat-germ agglutinin and concanavalin A. Considering all these characteristics, we propose that strains KM2 and H8 be designated as a new species: Acidiphilium symbioticum. The type strain of A. symbioticum is strain KM2 (= MTCC 566). Key words: Acidiphilium symbioticum, Acidiphilium cryptum, Thiobacillus ferrooxidans, acidophilic bacteria.