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Applied and Environmental Microbiology, July 1999, p. 3148-3157, Vol. 65, No. 7
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
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Nitrogen, Carbon, and Sulfur Metabolism in Natural
Thioploca Samples
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.
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