Search Results - (Author, Cooperation:D. C. Nelson)

2015-08-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Arabidopsis/*metabolism/*parasitology ; Arabidopsis Proteins/*classification/genetics/metabolism ; *Biological Evolution ; Gene Dosage ; Germination ; Heterocyclic Compounds, 1-Ring/*metabolism ; Host-Parasite Interactions ; Hydrolases/*classification/genetics/metabolism ; Lactones/*metabolism ; Orobanchaceae/*enzymology/genetics/growth & development ; Phylogeny ; Plant Growth Regulators/*metabolism ; Plant Roots/metabolism/parasitology ; Plants, Genetically Modified/genetics/metabolism

1432-1793

Springer Online Journal Archives 1860-2000

Biology

Abstract Certain hydrothermal vent invertebrates, e.g. Riftia pachyptila and Calyptogena magnifica, are clearly established as harboring dense populations of chemoautotrophic sulfur bacteria in specialized tissues. By contrast, the physiological characteristics of the abundant intracellular gill symbiont of the vent mussel Bathymodiolus thermophilus have been questioned. The low activities of enzymes diagnostic for CO2 fixation (Calvin cycle) and for sulfur-driven energy generation, as measured by other investigators, have been attributed to bacterial contamination of the gill surface. Based on research at the Galápagos Rift hydrothermal vents in 1988 and subsequent laboratory experiments, the current study confirms that the B. thermophilus symbiont is a psychrophile for which thiosulfate and sulfide stimulate CO2 fixation. It strongly indicates that the symbiont is a chemoautotroph by establishing the following: (1) Sulfide and thiosulfate can stimulate CO2 fixation by partially purified symbionts by up to 43-fold and 120-fold, respectively; (2) the ribulose-1,5-bisphosphate carboxylase/oxygenase activity of the symbiont is sufficient to account for its sulfide- or thiosulfate-stimulated CO2 incorporation; (3) the symbiont's molar growth yield on thiosulfate, as judged by CO2 incorporation, is indistinguishable from that of free-living chemoautotrophs. Due to the high protein-degrading activity of B. thermophilus gill lysate, it is also suggested that host lysis of symbionts plays a more important role in the nutrition of the vent mussel than in R. pachyptila or C. magnifica, for which no comparable protein-degrading activity was found.

Electronic Resource

1432-072X

Begglatoa spp. ; Ribulose-1,5-bisphosphate carboxylase ; Phosphoribulokinase ; Regulation of Calvin-cycle enzymes ; Heterologous gene-probe hybridization ; Non-autotrophic sulfur bacteria

Springer Online Journal Archives 1860-2000

Biology

Abstract To date only marine strains of the genus Beggiatoa have been proven to have the capacity for lithoautotrophic growth. The two best characterized freshwater strains (B18LD and OH-75-2a) — previously tested with no evidence of autotrophic potential — were reinvestigated in the current study. Heterotrophically grown cells from exponential or early stationary phase showed extremely low ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activities (0.002–0.2 nmol CO2·mg prot-1 min-1). After acetate limitation terminated growth both strains demonstrated increased RuBisCO activity with a maximum achieved 1–3 days into stationary phase. For a single growth cycle, activity could increase by more than 100-fold (strain OH-75-2a), but the highest activity achieved was less than 5% of that observed in a lithoautotrophic control. Phosphoribulokinase activity was approximately an order of magnitude greater than the corresponding RuBisCO activity and showed a similar pattern of regulation. A gene probe derived from the RuBisCO large subunit gene of Anacystis nidulans hybridized strongly with DNA from strain OH-75-2a and the autotrophic marine control but not with DNA from strain B18LD.

Electronic Resource