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Applied and Environmental Microbiology, July 2003, p. 3739-3750, Vol. 69, No. 7
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.7.3739-3750.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Characterization and In Situ Carbon Metabolism of Phototrophic Consortia

Jens Glaeser and Jörg Overmann^*

Bereich Mikrobiologie, Department I, Ludwig-Maximilians-Universität München, D-80638 Munich, Germany

Received 2 December 2002/ Accepted 17 March 2003

A dense population of the phototrophic consortium "Pelochromatium roseum" was investigated in the chemocline of a temperate holomictic lake (Lake Dagow, Brandenburg, Germany). Fluorescence in situ hybridization revealed that the brown epibionts of "P. roseum" constituted up to 37% of the total bacterial cell number and up to 88% of all green sulfur bacteria present in the chemocline. Specific amplification of 16S rRNA gene fragments of green sulfur bacteria and denaturing gradient gel electrophoresis fingerprinting yielded a maximum of four different DNA bands depending on the year of study, indicating that the diversity of green sulfur bacteria was low. The 465-bp 16S rRNA gene sequence of the epibiont of "P. roseum" was obtained after sorting of individual consortia by micromanipulation, followed by a highly sensitive PCR. The sequence obtained represents a new phylotype within the radiation of green sulfur bacteria. Maximum light-dependent H¹⁴CO₃^- fixation in the chemocline in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea suggested that there was anaerobic autotrophic growth of the green sulfur bacteria. The metabolism of the epibionts was further studied by determining stable carbon isotope ratios (¹³C) of their specific biomarkers. Analysis of photosynthetic pigments by high-performance liquid chromatography revealed the presence of high concentrations of bacteriochlorophyll (BChl) e and smaller amounts of BChl a and d and chlorophyll a in the chemocline. Unexpectedly, isorenieratene and ß-isorenieratene, carotenoids typical of other brown members of the green sulfur bacteria, were absent. Instead, four different esterifying alcohols of BChl e were isolated as biomarkers of green sulfur bacterial epibionts, and their ¹³C values were determined. Farnesol, tetradecanol, hexadecanol, and hexadecenol all were significantly enriched in ¹³C compared to bulk dissolved and particulate organic carbon and compared to the biomarkers of purple sulfur bacteria. The difference between the ¹³C values of farnesol, the major esterifying alcohol of BChl e, and CO₂ was -7.1%, which provides clear evidence that the mode of growth of the green sulfur bacterial epibionts of "P. roseum" in situ is photoautotrophic.

Present address: Justus Liebig Universität Gießen, Institut für Mikro- und Molekularbiologie, 35392 Gießen, Germany.

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