OCCURRENCE, STRUCTURE, AND METABOLIC-ACTIVITY OF THIODENDRON SULFUR MATS IN VARIOUS SALTWATER ENVIRONMENTS

It has been discovered that the colorless sulfur bacterium ''Thiodendr on latens'', which was believed to be rare, is, in fact, widely spread in marine benthic halophilic communities. We showed in the preceeding paper that Thiodendron on colonies and mats are composed of two struc tural components, anaerobic spirochetes and sulfate- and sulfur-reduce rs, which constitute a symbiotic association. We proposed to abolish t he genus Thiodendron. In this paper we refer to this association as '' Thiodendron''. Mats of ''Thiodendron'' occupy vast areas of sea bottom in highly productive shallow-water regions with intense inflow of hyd rogen sulfide of biogenic or geological origin. Such conditions are kn own to exist in littoral and sublittoral environments of the White Sea and Sea of Japan and in the regions of marine hydrothermal and volcan ic activity (Kraternaya Bay. the Kurile Islands. tile Pacific Ocean). ''Thiodendron'' mats develop in zones with concurrent inflow of hydrog en sulfide and oxygen. Development of the mat is accompanied by accumu lation of elemental sulfur in the cells of spirochetes. Radioisotopic studies have shown that ''Thiodendron'' mats exhibit a high sulfide ox idation rate, a considerable heterotrophic potential (glucose utilizat ion), and a low rate of dark heterotrophic assimilation of CO2. For th e first time free-living spirochetes have been shown to participate in the sulfur geochemical cycle coupled with destructive processes of ti le carbon cycle in marine ecosystems.