RESUMEN
Marine microbes are adapted to surviving in a variable phosphorus (P) environment. This adaptation frequently involves the presence of periplasmic or cell membrane-associated enzymes that enable them access to alternative sources of P when phosphate is depleted. In a recent study we identified the phosphatase PhoX as an enzyme that may be essential in mediating organic P acquisition in the ocean. Here we have investigated the role of this enzyme in the utilization of different P sources, using as a model the marine bacterium Ruegeria pomeroyi DSS-3. Although our previous study had demonstrated that PhoX accounts for more than 90% of the alkaline phosphatase (APase) activity in R. pomeroyi, a PhoX mutant strain was able to grow on monophosphate esters at the same rate as the wild type. Nevertheless, further APase kinetic analyses with both strains demonstrated that the Km of the wild-type strain was an order of magnitude lower than the mutant strain, indicating that PhoX is crucial for the use of these substrates at low concentrations, typically found in seawater. We also showed that PhoX is required for efficient hydrolysation of nucleotides like ADP and ATP.
RESUMEN
A hyperthermophilic, anaerobic archaeon was isolated from hydrothermal fluid samples obtained at the Okinawa Trough vents in the NE Pacific Ocean, at a depth of 1395m. The strain is obligately heterotrophic, and utilizes complex proteinaceous media (peptone, tryptone, or yeast extract), or a 21-amino-acid mixture supplemented with vitamins, as growth substrates. Sulfur greatly enhances growth. The cells are irregular cocci with a tuft of flagella, growing optimally at 98 degrees C (maximum growth temperature 102 degrees C), but capable of prolonged survival at 105 degrees C. Optimum growth was at pH 7 (range 5-8) and NaCl concentration 2.4% (range 1%-5%). Tryptophan was required for growth, in contrast to the closely related strains Pyrococcus furiosus and P. abyssi. Thin sections of the cell, viewed by transmission electron microscopy, revealed a periplasmic space similar in appearance to the envelope of P. furiosus. The predominant cell membrane component was tetraether lipid, with minor amounts of diether lipids. Treatment of the cells by mild osmotic shock released an extract that contained a Zn(2+)-dependent alkaline phosphatase. Phylogenetic analysis of the sequences encoding 16S rRNA and glutamate dehydrogenase places the isolate with certainty within the genus Pyrococcus although there is relatively low DNA-DNA hybridization (< 63%) with described species of this genus. Based on the reported results, we propose a new species, to be named Pyrococcus horikoshii sp.nov.
Asunto(s)
Pyrococcus/aislamiento & purificación , Japón , Filogenia , Pyrococcus/citología , Pyrococcus/genética , Pyrococcus/metabolismoRESUMEN
Uptake and autoradiography experiments with natural populations of marine bacteria, seawater cultures, and cultured isolates showed that the high-affinity cyclic AMP transport system in marine bacteria has stringent structural requirements, is found in a minority of cells in mixed bacterial assemblages, and appears to be related to the culture growth state.
RESUMEN
Zooplankton excretion and algal alkaline phosphatase are presumed to be responsible for phosphorus recycling in aquatic ecosystems; the role of bacteria has been unclear. High levels of bacterial cell-surface 5-nucleotidase were discovered in samples of picoplankton from California coastal waters. 5-Nucleotidase rapidly generated orthophosphate from 5-nucleotide added in nanomolar amounts and could supply half the orthophosphate required by plankton. Unlike alkaline phosphatase, 5-nucleotidase was not inhibited by orthophosphate at any concentration found in aquatic environments. Initial results indicate even greater 5-nucleotidase activity in fresh water (Lake Hodges, California) and brackish water (Baltic). Release and uptake of orthophosphate were tightly coupled.
RESUMEN
The major objective of this study was to describe the mechanism(s) of cyclic AMP uptake by natural populations of marine bacteria. A second objective was to determine whether this uptake could contribute to the intracellular regulatory pool of cyclic AMP. Using high-specific-activity P-labeled cyclic AMP, we found several high-affinity uptake systems. The highest-affinity system had a half-saturation constant of <10 pM. This system was extremely specific for cyclic nucleotides, particularly cyclic AMP. It appeared to meet the criteria for active transport. Uptake of cyclic AMP over a wide concentration range (up to 2 muM) showed multiphasic kinetics, with half-saturation constants of 1 nM and greater. These lower-affinity systems were much less specific for cyclic nucleotides. Although much of the labeled cyclic AMP taken up by the high-affinity systems was metabolized, some remained as intact cyclic AMP within the cells during 1 h of incubation. This suggests that at least some of the bacteria use cyclic AMP dissolved in seawater to augment their intracellular pools.