Ecophysiology of lithotrophic sulfur-oxidizing Sphaerotilus species from sulfide springs in the Northern Caucasus

Six strains of sulfur-oxidizing bacteria of the known organotrophic species Sphaerotilus natans were isolated from two North Caucasian sulfide springs. Similar to known colorless sulfur bacteria, all the strains accumulated elemental sulfur when grown in media with sulfide. Unlike previously isolated S. natans strains, new isolates had higher temperature growth optimum (33–37°C) and variable metabolism. All the strains were capable of organotrophic, lithoheterotrophic, and mixotrophic growth with sulfur compounds as electron donors for energy metabolism. Variable metabolism of new Sphaerotilus isolates is a highly important adaptation mechanism which facilitates extension of their geographic range and supports their mass development in new habitats, e.g. sulfide springs. Within the cluster of new isolates, the physiological heterogeneity was shown to result from the inducible nature of the enzymes of oxidative sulfur metabolism and from their resistance to aerobic cultivation.