Search

Members of the class Epsilonproteobacteria are known to be of major importance in biogeochemical processes at oxic-anosic interfaces. In pelagic redoxclines of the central Battic Sea, an uncultured epsilonproteobacterium related to Sulfurimonas denitrificans was proposed to play a key rote in chemolithotrophic denitrification (I. Brettar, M. Labrenz, S. Flavier. J. Bötel, H. Kuosa, R. Christen, and M. G. Höfle, AppI. Environ. Microbiol. 72:1364-1372, 2006). In order to determine the abundance, activity, and vertical distribution of this bacterium in high-resolotion profiles, 16S rRNA cloning and catalyzed reporter deposition and fluorescence in situ hybridization CARD-FISH) and quantitative PCR measurements were carried out. The results showed that 21% of the derived clone sequences, which in the present study were grouped together under the name GD17, had >99% similarity to the uncultured epsilonproteobacterium. A specific gene probe against GD17 (S-*-Sul-0090-a-4-18) was developed and used for enumeration hy CARD-FISH. In different pelagic redoxclines sampled during August 2003, May 2005, and February 2006, GD17 cells were always detected from the lower oxic area to the sulfidic area. Maximal abundance was detected around the chemocline, where sulfide and nitrate concentrations were close to the detection limit. The highest GD17 numbers 12 × 105 cells ml-1), representing up to 15% of the total bacteria, were comparable In those reported for Epsilonproteobacteria in pelagic redoxclines of the Black Sea and the Cariaco Trench (X. Lin, S. G. Wakeham, I. F. Putnam, Y. M. Astor, M. I. Scranton, A. Y. Chistoserdov, and G. T. Taylor, AppI. Environ. Microbiol. 72:2679-2690, 2006). However, in the Baltic Sea redoxclines, Epsilonproteobacteria consisted nearly entirely of cells belonging to the distinct GD17 group. This suggested that GD17 was the best-adapted epsilonproteobacterium within this ecological niche. [ABSTRACT FROM AUTHOR]

We have developed a highly sensitive approach to assess the abundance of uncultured bacteria in water samples from the central Baltic Sea by using a noncultured member of the “Epsilonproteobacteria” related to Thiomicrospira denitrificans as an example. Environmental seawater samples and samples enriched for the target taxon provided a unique opportunity to test the approach over a broad range of abundances. The approach is based on a combination of taxon- and domain-specific real-time PCR measurements determining the relative T. denitrificans-like 16S rRNA gene and 16S rRNA abundances, as well as the determination of total cell counts and environmental RNA content. It allowed quantification of T. denitrificans-like 16S rRNA molecules or 16S rRNA genes as well as calculation of the number of ribosomes per T. denitrificans-like cell. Every real-time measurement and its specific primer system were calibrated using environmental nucleic acids obtained from the original habitat for external standardization. These standards, as well as the respective samples to be measured, were prepared from the same DNA or RNA extract. Enrichment samples could be analyzed directly, whereas environmental templates had to be preamplified with general bacterial primers before quantification. Preamplification increased the sensitivity of the assay by more than 4 orders of magnitude. Quantification of enrichments with or without a preamplification step yielded comparable results. T. denitrificans-like 16S rRNA molecules ranged from 7.1 × 10³ to 4.4 × 109 copies ml-1 or 0.002 to 49.7% relative abundance. T. denitrificans-like 16S rRNA genes ranged from 9.0 × 10¹ to 2.2 × 106 copies ml-1 or 0.01 to 49.7% relative abundance. Detection limits of this real-time-PCR approach were 20 16S rRNA molecules or 0.2 16S rRNA gene ml-1. The number of ribosomes per T. denitrificans-like cell was estimated to range from 20 to 200 in seawater and reached up to 2,000 in the enrichments. The results indicate that our real-time PCR approach can be used to determine cellular and relative abundances of uncultured marine bacterial taxa and to provide information about their levels of activity in their natural environment. [ABSTRACT FROM AUTHOR]

Recent studies have indicated that chemoautotrophic Epsilonproteobacteria might play an important role, especially as anaerobic or microaerophilic dark CO[sub2]-fixing organisms, in marine pelagic redoxclines. However, knowledge of their distribution and abundance as actively CO[sub2]-fixing microorganisms in pelagic redoxclines is still deficient. We determined the contribution of Epsilonproteobacteria to dark CO[sub2] fixation in the sulfidic areas of central Baltic Sea and Black Sea redoxclines by combining catalyzed reporter deposition-fluorescence in situ hybridization with microautoradiography using [[sup14]C]bicarbonate and compared it to the total prokaryotic chemoautotrophic activity. In absolute numbers, up to 3 x 10[sup5] [sup14]CO[sub2]-fixing prokaryotic cells ml[sup-1] were enumerated in the redoxcline of the central Baltic Sea and up to 9 x 10[sup4] [sup14]CO[sub2]-fixing cells ml[sup-1] were enumerated in the Black Sea redoxcline, corresponding to 29% and 12%, respectively, of total cell abundance. [sup14]CO[sub2]-incorporating cells belonged exclusively to the domain Bacteria. Among these, members of the Epsilonproteobacteria were approximately 70% of the cells in the central Baltic Sea and up to 100% in the Black Sea. For the Baltic Sea, the Sulfurimonas subgroup GD17, previously assumed to be involved in autotrophic denitrification, was the most dominant CO[sub2]-fixing group. In conclusion, Epsilonproteobacteria were found to be mainly responsible for chemoautotrophic activity in the dark CO[sub2] fixation maxima of the Black Sea and central Baltic Sea redoxclines. These Epsilonproteobacteria might be relevant in similar habitats of the world's oceans, where high dark CO[sub2] fixation rates have been measured. [ABSTRACT FROM AUTHOR]