Genetic Variation among Endosymbionts of Widely Distributed Vestimentiferan Tubeworms

Vestimentiferan tubeworms thriving in sulfidic deep-sea hydrothermal vents and cold seeps are constrained by their nutritional reliance on chemoautotrophic endosymbionts. In a recent phylogenetic study using 16S ribosomal DNA, we found that endosymbionts from vent and seep habitats form two distinct clades with little variation within each clade. In the present study, we used two different approaches to assess the genetic variation among biogeographically distinct vestimentiferan symbionts. DNA sequences were obtained for the noncoding, internal transcribed spacer (ITS) regions of the rRNA operons of symbionts associated with six different genera of vestimentiferan tubeworms. ITS sequences from endosymbionts of host genera collected from different habitats and widely distributed vent sites were surprisingly conserved. Because the ITS region was not sufficient for distinguishing endosymbionts from different habitats or locations, we used a DNA fingerprinting technique, repetitive-extragenic-palindrome PCR (REP-PCR), to reveal differences in the distribution of repetitive sequences in the genomes of the bacterial endosymbionts. Most of the endosymbionts displayed unique REP-PCR patterns. A cladogram generated from these fingerprints reflected relationships that may be influenced by a variety of factors, including host genera, geographic location, and bottom type.     

Not whale-fall specialists, Osedax worms also consume fishbones

Marine annelid worms of the genus Osedax exploit sunken vertebrate bones for food. To date, the named species occur on whale or other mammalian bones, and it is argued that Osedax is a whale-fall specialist. To assess whether extant Osedax species could obtain nutrition from non-mammalian resources, we deployed teleost bones and calcified shark cartilage at approximately 1000 m depth for five months. Although the evidence from shark cartilage was inconclusive, the teleost bones hosted three species of Osedax, each of which also lives off whalebones. This suggests that rather than being a whale-fall specialist, Osedax has exploited and continues to exploit a variety of food sources. The ability of Osedax to colonize and to grow on fishbone lends credibility to a hypothesis that it might have split from its siboglinid relatives to assume the bone-eating lifestyle during the Cretaceous, well before the origin of marine mammals.     

A genetic element present on megaplasmids allows Enterococcus faecium to use raffinose as carbon source

Enterococcus faecium is a commensal of the gastrointestinal tract of humans and animals. Since the 1990s, it has also emerged as a nosocomial pathogen. Little is known about carbon metabolism of E. faecium even though the ability to utilize different sugars could be an important factor in adapting to different ecological niches. In this study we identify an E. faecium gene cluster that is responsible for the metabolism of the α-galactoside sugar raffinose. Phenotypic testing of seven E. faecium isolates of which the genomes were previously sequenced showed that one isolate (strain E980) could grow on raffinose. Genome analysis identified a gene cluster containing two genes encoding α-galactosidases (termed agaA and agaB) that was uniquely present in E980. The agaA and agaB genes were significantly more frequently found in strains that are phylogenetically related to E980 and were more prevalent in surveillance isolates from hospital and community sources than in isolates from clinical infections. Disruption of the α-galactosidase gene agaB, but not of agaA, disabled growth on raffinose in strain E980. In all strains agaA and agaB are carried on megaplasmids that are between 150 and 300 kb in size. Filter-mating experiments showed that the megaplasmid of E980 can be transferred to a plasmidless recipient which then gains the ability to grow on raffinose. The observation that raffinose utilization by E. faecium is a trait carried by megaplasmids indicates that these megaplasmids can have important roles in shaping the competitive fitness of E. faecium in the environment, for example by expanding the metabolic repertoire of this organism.     

Molecular taxonomy reveals broad trans-oceanic distributions and high species diversity of deep-sea clams (Bivalvia: Vesicomyidae: Pliocardiinae) in chemosynthetic environments

Large vesicomyid clams are common inhabitants of sulphidic deep-sea habitats such as hydrothermal vents, hydrocarbon seeps and whale-falls. Yet, the species- and genus-level taxonomy of these diverse clams has been unstable due to insufficiencies in sampling and absence of detailed taxonomic studies that would consistently compare molecular and morphological characters. To clarify uncertainties about species-level assignments, we examined DNA sequences from mitochondrial cytochrome-c-oxidase subunit I (COI) in conjunction with morphological characters. New and published COI sequences were used to create a molecular database for 44 unique evolutionary lineages corresponding to species. Overall, the congruence between molecular and morphological characters was good. Several discrepancies due to synonymous species designations were recognized, and acceptable species names were rectified with published COI sequences in cases where morphological specimens were available. We identified seven species with trans-Pacific distributions, and two species with Indo-Pacific distributions. Presently, 27 species have only been documented from one region, which might reflect limited ranges, or insufficient geographical sampling. Vesicomyids exhibit the greatest species diversity along the northwest Pacific ridge systems and in the eastern Pacific, along the western America margin, where depth zonation typically results in segregation of closely related species. The broad distributions of several vesicomyid species suggest that their required chemosynthetic habitats might be more common than previously recognized and occur along most continental margins.     

Survival of Desulfotomaculum spores from estuarine sediments after serial autoclaving and high-temperature exposure

Bacterial spores are widespread in marine sediments, including those of thermophilic, sulphate-reducing bacteria, which have a high minimum growth temperature making it unlikely that they grow in situ. These Desulfotomaculum spp. are thought to be from hot environments and are distributed by ocean currents. Their cells and spores upper temperature limit for survival is unknown, as is whether they can survive repeated high-temperature exposure that might occur in hydrothermal systems. This was investigated by incubating estuarine sediments significantly above (40–80 °C) maximum in situ temperatures (∼23 °C), and with and without prior triple autoclaving. Sulphate reduction occurred at 40–60 °C and at 60 °C was unaffected by autoclaving. Desulfotomaculum sp. C1A60 was isolated and was most closely related to the thermophilic D. kuznetsovii^T (∼96% 16S rRNA gene sequence identity). Cultures of Desulfotomaculum sp. C1A60, D. kuznetsovii^Tand D. geothermicum B2T survived triple autoclaving while other related Desulfotomaculum spp. did not, although they did survive pasteurisation. Desulfotomaculum sp. C1A60 and D. kuznetsovii cultures also survived more extreme autoclaving (C1A60, 130 °C for 15 min; D. kuznetsovii, 135 °C for 15 min, maximum of 154 °C reached) and high-temperature conditions in an oil bath (C1A60, 130° for 30 min, D. kuznetsovii 140 °C for 15 min). Desulfotomaculum sp. C1A60 with either spores or predominantly vegetative cells demonstrated that surviving triple autoclaving was due to spores. Spores also had very high culturability compared with vegetative cells (∼30 × higher). Combined extreme temperature survival and high culturability of some thermophilic Desulfotomaculum spp. make them very effective colonisers of hot environments, which is consistent with their presence in subsurface geothermal waters and petroleum reservoirs.     

A remarkable diversity of bone-eating worms (Osedax; Siboglinidae; Annelida)

Background

We previously showed that mice lacking the high mobility group A1 gene (Hmga1-knockout mice) developed a type 2-like diabetic phenotype, in which cell-surface insulin receptors were dramatically reduced (below 10% of those in the controls) in the major targets of insulin action, and glucose intolerance was associated with increased peripheral insulin sensitivity. This particular phenotype supports the existence of compensatory mechanisms of insulin resistance that promote glucose uptake and disposal in peripheral tissues by either insulin-dependent or insulin-independent mechanisms. We explored the role of these mechanisms in the regulation of glucose homeostasis by studying the Hmga1-knockout mouse model. Also, the hypothesis that increased insulin sensitivity in Hmga1-deficient mice could be related to the deficit of an insulin resistance factor is discussed.

Results

We first show that HMGA1 is needed for basal and cAMP-induced retinol-binding protein 4 (RBP4) gene and protein expression in living cells of both human and mouse origin. Then, by employing the Hmga1-knockout mouse model, we provide evidence for the identification of a novel biochemical pathway involving HMGA1 and the RBP4, whose activation by the cAMP-signaling pathway may play an essential role for maintaining glucose metabolism homeostasis in vivo, in certain adverse metabolic conditions in which insulin action is precluded. In comparative studies of normal and mutant mice, glucagon administration caused a considerable upregulation of HMGA1 and RBP4 expression both at the mRNA and protein level in wild-type animals. Conversely, in Hmga1-knockout mice, basal and glucagon-mediated expression of RBP4 was severely attenuated and correlated inversely with increased Glut4 mRNA and protein abundance in skeletal muscle and fat, in which the activation state of the protein kinase Akt, an important downstream mediator of the metabolic effects of insulin on Glut4 translocation and carbohydrate metabolism, was simultaneously increased.

Conclusion

These results indicate that HMGA1 is an important modulator of RBP4 gene expression in vivo. Further, they provide evidence for the identification of a novel biochemical pathway involving the cAMP-HMGA1-RBP4 system, whose activation may play a role in glucose homeostasis in both rodents and humans. Elucidating these mechanisms has importance for both fundamental biology and therapeutic implications.