Geodia barretti is a marine cold-water sponge harbouring high numbers of microorganisms. Significant rates of nitrification have been observed in this sponge, indicating a substantial contribution to nitrogen turnover in marine environments with high sponge cover. In order to get closer insights into the phylogeny and function of the active microbial community and the interaction with its host G. barretti, a metatranscriptomic approach was employed, using the simultaneous analysis of rRNA and mRNA. Of the 262 298 RNA-tags obtained by pyrosequencing, 92% were assigned to ribosomal RNA (ribo-tags). A total of 109 325 SSU rRNA ribo-tags revealed a detailed picture of the community, dominated by group SAR202 of Chloroflexi, candidate phylum Poribacteria and Acidobacteria, which was different in its composition from that obtained in clone libraries prepared form the same samples. Optimized assembly strategies allowed the reconstruction of full-length rRNA sequences from the short ribo-tags for more detailed phylogenetic studies of the dominant taxa. Cells of several phyla were visualized by FISH analyses for confirmation. Of the remaining 21 325 RNA-tags, 10 023 were assigned to mRNA-tags, based on similarities to genes in the databases. A wide range of putative functional gene transcripts from over 10 different phyla were identified among the bacterial mRNA-tags. The most abundant mRNAs were those encoding key metabolic enzymes of nitrification from ammonia-oxidizing archaea as well as candidate genes involved in related processes. Our analysis demonstrates the potential and limits of using a combined rRNA and mRNA approach to explore the microbial community profile, phylogenetic assignments and metabolic activities of a complex, but little explored microbial community.

Deep-sea hydrothermal vents are unique environments on Earth, as they host chemosynthetic ecosystems fuelled by geochemical energy with chemolithoautotrophic microorganisms at the basis of the food webs. Whereas discrete high-temperature venting systems have been studied extensively, the microbiotas associated with low-temperature diffuse venting are not well understood. We analysed the structure and functioning of microbial communities in two diffuse venting sediments from the Jan Mayen vent fields in the Norwegian-Greenland Sea, applying an integrated 'omics' approach combining metatranscriptomics, metaproteomics and metagenomics. Polymerase chain reaction-independent three-domain community profiling showed that the two sediments hosted highly similar communities dominated by Epsilonproteobacteria, Deltaproteobacteria and Gammaproteobacteria, besides ciliates, nematodes and various archaeal taxa. Active metabolic pathways were identified through transcripts and peptides, with genes of sulphur and methane oxidation, and carbon fixation pathways highly expressed, in addition to genes of aerobic and anaerobic (nitrate and sulphate) respiratory chains. High expression of chemotaxis and flagella genes reflected a lifestyle in a dynamic habitat rich in physico-chemical gradients. The major metabolic pathways could be assigned to distinct taxonomic groups, thus enabling hypotheses about the function of the different prokaryotic and eukaryotic taxa. This study advances our understanding of the functioning of microbial communities in diffuse hydrothermal venting sediments.

Marine nematodes that carry sulfur-oxidizing bacteria on their cuticle (Stilbonematinae, Desmodoridae) migrate between oxidized and reduced sand layers thereby supplying their symbionts with oxygen and sulfide. These symbionts, in turn, constitute the worms' major food source. Due to the accessibility, abundance and relative simplicity of this association, stilbonematids may be useful to understand symbiosis establishment. Nevertheless, only the symbiont of Laxus oneistus has been found to constitute one single phylotype within the Gammaproteobacteria. Here, we characterized the symbionts of three yet undescribed nematodes that were morphologically identified as members of the genus Robbea. They were collected at the island of Corsica, the Cayman Islands and the Belize Barrier Reef. The surface of these worms is covered by a single layer of morphologically undistinguishable bacteria. 18S rDNA-based phylogenetic analysis showed that all three species belong to the Stilbonematinae, although they do not form a distinct cluster within that subfamily. 16S rDNA-based analysis of the symbionts placed them interspersed in the cluster comprising the sulfur-oxidizing symbionts of L. oneistus and of marine gutless oligochaetes. Finally, the presence and phylogeny of the aprA gene indicated that the symbionts of all three nematodes can use reduced sulfur compounds as an energy source.

Abstract. The search for chemically peculiar (CP) stars in open clusters using photoelectric photometry sampling the presence of the characteristic flux depression feature at 5200Å via the ∆a-system (Maitzen 1976) has so far delivered data for objects usually no more distant than 1000 pc from the Sun. A series of fourteen papers (first: Maitzen & Hensberge 1981; for the time being last: Maitzen 1993) were devoted to 1240 stars in 38 open cluster fields.If one intends to study the presence of CP stars at larger distances from the Sun, classical photometry has to be replaced by CCD photometry. We have therefore initialized in 1995 a new survey in open clusters and the Large Magellanic Cloud using the CCD technology.As a first step, we have presented new ∆a-photometry of 22 CP2 stars in the galactic field to prove the capability of CCD photometry for our aim (Maitzen et al. 1997).In the first paper of a new series devoted to CCD photometry, we present data on NGC 2169 (13 stars investigated), Melotte 105 (114 stars), and NGC 6250 (48 stars). NGC 2169 was used to test our results with those of classical photometry which yields excellent agreement.For NGC 6250 we find two new definite CP2 (according to the definition by Preston 1974) stars (∆a = 0.065 and 0.026 mag) and two λ Bootis candidates. Twelve objects with only marginally peculiar ∆a-values for Melotte 105 were detected. Additional spectroscopic and photometric evidence is needed to substantiate their peculiarity.

Marine oligochaete and nematode thiotrophic symbionts (MONTS) form a phylogenetic cluster within the Gammaproteobacteria. For the symbionts that live on the nematode surface, environmental transmission is likely. However, until now, no free-living relatives have been found. In this study, we detected MONTS cluster members in offshore surface seawater of both the Caribbean and the Mediterranean Sea by PCR amplification of their 16S rRNA genes. This is the first evidence of members of this cluster in the pelagic environment. These may either be free-living forms of the symbionts or closely related, nonsymbiotic strains. In either case, their existence sheds light on the evolution of beneficial symbioses between shallow water invertebrates and sulfur-oxidizing bacteria.