An ecological study of the sulfur-oxidizing bacteria from the littoral zone of a michigan lake and a sulfur spring in Florida

Abstract

The sulfur-oxidizing communities of decomposing plants in a Michigan Lake and of a sub-tropical sulfur spring were studied using anin situ gradient enrichment method, electron microscopy, light microscopy and plating techniques. Oxygen tolerant and aerobic sulfur-oxidizing bacteria were found attached to plant surfaces either by a holdfast or by mucilage which encased microcolonies. Thiothrix and Thiocystis were commonly observed by microscopy on decomposing plant material.In situ thiosulfate gradient enrichments with plant material as inocula selected fluorescent pseudomonads rather than Thiobacilli and resulted in a three-fold increase in growth-rate as the thiosulfate concentration increased from 55 µg/l to 1 g/l sodium thiosulfate. Isolate TBT-H, a fluorescent pseudomonad, andPseudomonas aeruginosa were found to produce sulfide-binding ‘exudates’ which yielded globules of elemental sulfur. The active ‘exudate’ was only produced by organisms with fluorescent pigments and only in media containing S2O3=, which also stimulated fluorescent pigment production.