Thioploca spp: filamentous sulfur bacteria with nitrate vacuoles

Thioploca spp. are multicellular, filamentous, colorless sulfur bacteria in habiting freshwater and marine sediments. They have elemental sulfur inclus ions similar to the phylogenetically closely related Beggiatoa, but in cont rast to these they live in bundles surrounded by a common sheath. Vast comm unities of large Thioploca species live along the Pacific coast of South Am erica and in other upwelling areas of high organic matter sedimentation wit h bottom waters poor in oxygen and rich in nitrate. Each cell of these thio plocas harbors a large liquid vacuole which is used as a storage for nitrat e with a concentration of lip to 506 mM. The nitrate is used as an electron acceptor for sulfide oxidation and the bacteria may grow autotrophically o r mixotrophically using acetate or other organic molecules as carbon source . The filaments stretch up into the overlying seawater, from which they tak e up nitrate, and then glide down 5-15 cm deep into the sediment through th eir sheaths to oxidize sulfide formed by intensive sulfate reduction. New m ajor occurrences have bren found in recent years, both in lakes and in the ocean, and have stimulated the interest in these fascinating bacteria. (C) 1999 Federation of European Microbiological Societies. Published by Elsevie r Science B.V. All rights reserved.