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Applied and Environmental Microbiology, July 1999, p. 3148-3157, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Nitrogen, Carbon, and Sulfur Metabolism in Natural Thioploca Samples

Sandra Otte,1 J. Gijs Kuenen,1,* Lars P. Nielsen,2 Hans W. Paerl,3 Jakob Zopfi,4 Heide N. Schulz,4 Andreas Teske,5 Bettina Strotmann,3 Victor A. Gallardo,6 and Bo B. Jørgensen3

Department of Biotechnology, Kluyver Laboratory for Biotechnology, Delft University of Technology, Delft, The Netherlands1; Institute of Biological Sciences, University of Aarhus, Aarhus, Denmark2; Max Planck Institute for Marine Microbiology, Bremen, Germany4; Institute of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina3; Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts5; and Departamento de Oceanografia, Universidad de Concepción, Concepción, Chile6

Received 8 December 1998/Accepted 7 May 1999

Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with 15N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min-1 mg of protein-1. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min-1 mg of protein-1. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min-1 mg of protein-1 and could be increased to 10.7 nmol min-1 mg of protein-1 after the trichomes were starved for 45 h. Incorporation of 14CO2 was at a rate of 0.4 to 0.8 nmol min-1 mg of protein-1, which is half the rate calculated from sulfide oxidation. [2-14C]acetate incorporation was 0.4 nmol min-1 mg of protein-1, which is equal to the CO2 fixation rate, and no 14CO2 production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-14C]acetate, with only a minor contribution by epibiontic bacteria present in the samples.

* Corresponding author. Mailing address: Delft University of Technology, Kluyver Laboratory for Biotechnology, Julianalaan 67, 2628 BC, The Netherlands. Phone: 31 15 2782416. Fax: 31 15 2782355. E-mail: J.G.Kuenen{at}STM.TUDelft.nl.

Applied and Environmental Microbiology, July 1999, p. 3148-3157, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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