MEPS 183:149-158 (1999)  -  doi:10.3354/meps183149

Metabolism of nitrogen and sulfur in ectosymbiotic bacteria of marine nematodes (Nematoda, Stilbonematinae)

U. Hentschel1,*, E. C. Berger2, M. Bright2, H. Felbeck3, J. A. Ott2

1Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070 Würzburg, Germany
2Institut für Zoologie, Universität Wien, A-1090 Vienna, Austria
3Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, California 92093, USA

ABSTRACT: Nematodes of the family Stilbonematinae are known for their highly specific association with ectosymbiotic bacteria. These worms are members of the meiofauna in marine, sulfide-rich sediments, where they migrate around the redox boundary layer. In this study, bacterial ectosymbionts of 2 species of marine nematodes, Stilbonema sp. and Laxus oneistus, were shown to be capable of the respiratory reduction of nitrate and nitrite (denitrification). The use of these alternative electron acceptors to oxygen by the bacteria allows the animals to migrate into the deeper, anoxic sediments, where they can exploit the sulfide-rich patches of the deeper sediment layers. The accumulation of thiols (sulfide, thiosulfate, sulfate and glutathione) in body tissues of the worms was determined following incubation in the presence of various electron donors (sulfide, thiosulfate) and acceptors (nitrate). In their chemoautotrophic metabolic potential, the ectosymbionts of the 2 nematode species were found to resemble the phylogenetically related, intracellular symbionts of macrofaunal hosts of deep-sea hydrothermal vents and other sulfide-rich habitats.

KEY WORDS: Stilbonematinae · Symbiosis · Chemoautotrophy · Sulfide · Denitrification

Full text in pdf format