Microbiological processes of the carbon and sulfur cycles at cold methane seeps of the North Atlantic

Functioning of microbial communities in surface sediments of the Haakon Mos by underwater mud volcano (lat. 72 degreesN) and in gas seepage fields of t he Vestnesa Ridge was investigated using Mil I and Mir-2 deep-sea submersib les during the 40th voyage of the research vessel Academician Mstislav Keld ysh. Large areas of sedimentary deposits of the Haakon Mosby mud volcano (H MMV) and pockmarks of the Vestnesa Ridge (VR) are covered with bacterial ma ts 0.1 to 0.5 cm thick, The microbial community making up bacterial mats of the HMMV was dominated by large filamentous bacteria with filaments measur ing up to 100 mum in length and 2 to 8 mum in width. The occurrence of rose ttes allowed the observed filamentous bacteria to be referred to the morpho logically similar genera Leucothrix or Thiothrix. Three morphological types of filamentous bacteria were identified in bacterial mats covering VR pock marks. Filaments of type one are morphologically similar with representativ es of the genera Thioploca or Desmanthos. Type two filaments had numerous i nclusions of sulfur and resembled representatives of the genus Thiothrix. T he third morphological type was constituted by single filaments made up of tightly connected disk-like cells and can be assigned to the genus Beggiato a, The rates of methane oxidation (up to 1570 mul C/(dm(3) day)) and sulfat e reduction (up to 17 mg S/(dm(3)day)) measured in the surface sediments of HMMV and VR were close to the maximum rates of these processes observed in heavily polluted regions of the northwestern shelf of the Black Sea. High rates of microbiological processes correlated with the high number of bacte ria. The rate of methane production in sediments studied was notably lower and ranged from 0.1 to 3.5 mu CH4/(dm(3)day). Large areas of the HMMV calde ra were populated by pogonophoras, represented by the two species Sclerolin um sp. and Oligobrachia sp. The mass development of Sclerolinum sp. in the HMMV caldera was by the activity of aerobic methane-oxidizing bacteria loca lized inside the cells of these animals. Bacterial cells were also found in the trophosome tissue of Oligobrachia sp., but in cells of these bacteria, we did not observe the membrane structures typical of methanotrophs. The l ocalization pattern of pogonophoras on the surface of reduced sediments sug gests that the predominant bacteria in Oligobrachia tissues are sulfur-oxid izing endosymbionts.