To assess the risk that mining of seafloor massive sulfides (SMS) from extinct hydrothermal vent environments has for changing the ecosystem irreversibly, we sampled SMS analogous habitats from the Kairei and the Pelagia vent fields along the Indian Ridge. In total 19.8 million 16S rRNA tags from 14 different sites were analyzed and the microbial communities were compared with each other and with publicly available data sets from other marine environments. The chimneys appear to provide habitats for microorganisms that are not found or only detectable in very low numbers in other marine habitats. The chimneys also host rare organisms and may function as a vital part of the ocean’s seed bank. Many of the reads from active and inactive chimney samples were clustered into OTUs, with low or no resemblance to known species. Since we are unaware of the chemical reactions catalyzed by these unknown organisms, the impact of this diversity loss and bio-geo-coupling is hard to predict. Given that chimney structures can be considered SMS analogues, removal of sulfide deposits from the seafloor in the Kairei and Pelagia fields will most likely alter microbial compositions and affect element cycling in the benthic regions and probably beyond.

Deep-sea hydrothermal vents may provide one of the largest reservoirs on Earth for hydrogen-oxidizing microorganisms. Depending on the type of geological setting, hydrothermal environments can be considerably enriched in hydrogen (up to millimolar concentrations). As hot, reduced hydrothermal fluids ascend to the seafloor they mix with entrained cold, oxygenated seawater, forming thermal and chemical gradients along their fluid pathways. Consequently, in these thermally and chemically dynamic habitats biochemically distinct hydrogenases (adapted to various temperature regimes, oxygen and hydrogen concentrations) from physiologically and phylogenetically diverse Bacteria and Archaea can be expected. Hydrogen oxidation is one of the important inorganic energy sources in these habitats, capable of providing relatively large amounts of energy (237 kJ/mol H2) for driving ATP synthesis and autotrophic CO2 fixation. Therefore, hydrogen-oxidizing organisms play a key role in deep-sea hydrothermal vent ecosystems as they can be considerably involved in light-independent primary biomass production. So far, the specific role of hydrogen-utilizing microorganisms in deep-sea hydrothermal ecosystems has been investigated by isolating hydrogen-oxidizers, measuring hydrogen consumption (ex situ), studying hydrogenase gene distribution and more recently by analyzing metatranscriptomic and metaproteomic data. Here we summarize this available knowledge and discuss the advent of new techniques for the identification of novel hydrogen-uptake and -evolving enzymes from hydrothermal vent microorganisms.

Hydrogen is one of the most common elements on Earth. The enzymes converting molecular hydrogen into protons and electrons are the hydrogenases. Hydrogenases are ubiquitously distributed in all three domains of life where they play a central role in cell metabolism. So far, the recovery of hydrogenases has been restricted to culture-dependent and sequence-based approaches. We have recently developed the only activity-based screen for seeking H-uptake enzymes from metagenomes without having to rely on enrichment and isolation of hydrogen-oxidizing microorganisms or prior metagenomic sequencing. When screening 14,400 fosmid clones from three hydrothermal vent metagenomes using this solely activity-based approach, four clones with H-uptake activity were identified with specific activities of up to 258 ± 19 nmol H/min/mg protein of partially purified membrane fractions. The respective metagenomic fragments exhibited mostly very low or no similarities to sequences in the public databases. A search with hidden Markov models for different hydrogenase groups showed no hits for three of the four metagenomic inserts, indicating that they do not encode for classical hydrogenases. Our activity-based screen serves as a powerful tool for the discovery of (novel) hydrogenases which would not have been identified by the currently available techniques. This screen can be ideally combined with culture- and sequence-based approaches to investigate the tremendous hydrogen-converting potential in the environment.

Genomic and cDNA clones, encoding a protein that is a member of the guanine nucleotide-binding regulatory protein (G protein)-coupled receptor superfamily, were isolated by screening rat genomic and thoracic aorta cDNA libraries with an oligonucleotide encoding a highly conserved region of the Ml muscarinic acetylcholine receptor. Sequence analyses of these clones showed that they encode a 343-amino acid protein (named RTA). The RTA gene is single copy, as demonstrated by restriction mapping and Southern blotting of genomic clones and rat genomic DNA. Sequence analysis of the genomic clone further showed that the RTA gene has an intron interrupting the region encoding the amino terminus of the protein. RTA RNA sequences are relatively abundant throughout the gut, vas deferens, uterus, and aorta but are only barely detectable (on Northern blots) in liver, kidney, lung, and salivary gland. In the rat brain, RTA sequences are markedly abundant in the cerebellum. RTA is most closely related to the mas oncogene (34% identity), which has been suggested to be a forebrain angiotensin receptor. We cannot detect angiotensin binding to the RTA protein after introducing the cognate cDNA or mRNA into COS cells or Xenopus oocytes, respectively, nor can we detect an electrophysiologic response in the oocyte after application of angiotensin peptides. We conclude that RTA is not an angiotensin receptor; to date, we have been unable to identify its ligand.An interesting recent development in receptor biology has been the realization that many of the receptors interacting with the guanine nucleotide-binding regulatory protein (G protein) signaling system are homologues. The mammalian members of this receptor superfamily described to date by molecular cloning include ,B-adrenergic (1-3), a-adrenergic (4-6), muscarinic acetylcholine (7-10), serotonin (11-14), dopamine (15), substances K (16) and P (17), luteinizing hormone (18,19), and rhodopsin (20) receptors. The quintessential feature of these proteins is seven stretches of 20-26 hydrophobic amino acids; these regions, which are the most conserved regions among different receptors, are thought to form a-helices that span the cytoplasmic membrane. Other features common to these proteins include one or more potential N-linked glycosylation sites near the amino terminus, the lack of a discernible amino-terminal signal peptide (except the luteinizing hormone receptor) (18,19), and several invariant amino acid residues. Another feature of this family is that the coding regions of the genes often lack introns; exceptions to this trend include bovine rhodopsin (20) and D2 subtype of the dopamine receptor (15). A currently popular model proposes that these proteins have their amino terminus outside the cell and the seven hydrophobic segments spanning the cytoplasmic membrane with the connecting segments alternately extending into the cytoplasm and the extracellular space and the carboxyl terminus inside the cell. The evidence for this structure is largely an extrapolation from re...