Occurrence of beta-Aminoglutaric Acid in Marine Bacteria.

beta-Aminoglutaric acid, a nonprotein amino acid isomer of glutamic acid, was found in the free amino acid pool of a marine bacterium, Alteromonas luteoviolacea. It was also found in a mixed culture of fermenting bacteria enriched from an anoxic marine sediment.

Assimilatory Sulfur Metabolism in Marine Microorganisms: Sulfur Metabolism, Protein Synthesis, and Growth of Alteromonas luteo-violaceus and Pseudomonas halodurans During Perturbed Batch Growth.

The antibiotic protein synthesis inhibitor chloramphenicol specifically blocked the incorporation of [S]sulfate into the residue protein of two marine bacteria, Pseudomonas halodurans and Alteromonas luteo-violaceus. Simultaneous inhibition of total protein synthesis occurred, but incorporation of S into low-molecular-weight organic compounds continued. A. luteo-violaceus rapidly autolyzed, with similar reduction in cell counts, total culture protein and cellular sulfur, whereas P. halodurans remained viable. Treatment with chloramphenicol, growth during nitrogen and carbon limitation, and the carbon and energy sources used for growth did not alter the sulfur content of P. halodurans protein. The mean value (1.09%, by weight), representing a wide variety of environmentally relevant growth conditions, was in agreement with model protein composition. The variability of cellular composition of P. halodurans and A. luteo-violaceus is discussed with respect to the measurement of bacterial growth in natural environments. Total carbon and nitrogen per cell varied greatly (coefficient of variation, ca. 100%) depending on growth conditions. Variation in total sulfur and protein per cell was much less (coefficient of variation, <50%), but the least variation was found for sulfate incorporation into residue protein (coefficient of variation, ca. 15%). Thus, sulfate incorporation into residue protein can be used as an accurate measurement of de novo protein synthesis in these bacteria.

Assimilatory sulfur metabolism in marine microorganisms: considerations for the application of sulfate incorporation into protein as a measurement of natural population protein synthesis.

The sulfur content of residue protein was determined for pure cultures of Nitrosococcus oceanus, Desulfovibrio salexigens, 4 mixed populations of fermentative bacteria, 22 samples from mixed natural population enrichments, and 11 nutritionally and morphologically distinct isolates from enrichments of Sargasso Sea water. The average 1.09 +/- 0.14% (by weight) S in protein for 13 pure cultures agrees with the 1.1% calculated from average protein composition. An operational value encompassing all mixed population and pure culture measurements has a coefficient of variation of only 15.1% (n = 41). Short-term [S]sulfate incorporation kinetics by Pseudomonas halodurans and Alteromonas luteoviolaceus demonstrated a rapid appearance of S in the residue protein fraction which was well modelled by a simple exponential uptake equation. This indicates that little error in protein synthesis determination results from isotope dilution by endogenous pools of sulfur-containing compounds. Methionine effectively competed with sulfate for protein synthesis in P. halodurans at high concentrations (10 muM), but had much less influence at 1 muM. Cystine competed less effectively with sulfate, and glutathione did not detectably reduce sulfate-S incorporation into protein. [S]sulfate incorporation was compared with [C]glucose assimilation in a eutrophic brackish-water environment. Both tracers yielded similar results for the first 8 h of incubation, but a secondary growth phase was observed only with S. Redistribution of C from low-molecular-weight materials into residue protein indicated additional protein synthesis. [S]sulfate incorporation into residue protein by marine bacteria can be used to quantitatively measure bacterial protein synthesis in unenriched mixed populations of marine bacteria.

Assimilatory sulfur metabolism in marine microorganisms: characteristics and regulation of sulfate transport in Pseudomonas halodurans and Alteromonas luteo-violaceus.

Sulfate transport capacity was not regulated by cysteine, methionine, or glutathione in Pseudomonas halodurans, but growth on sulfate or thiosulfate suppressed transport. Subsequent sulfur starvation of cultures grown on all sulfur sources except glutathione stimulated uptake. Only methionine failed to regulate sulfate transport in Alteromonas luteo-violaceus, and sulfur starvation of all cultures enhanced transport capacity. During sulfur starvation of sulfate-grown cultures of both bacteria, the increase in transport capacity was mirrored by a decrease in the low-molecular-weight organic sulfur pool. Little metabolism of endogenous inorganic sulfate occurred. Cysteine was probably the major regulatory compound in A. luteo-violaceus, but an intermediate in sulfate reduction, between sulfate and cysteine, controlled sulfate transport in P. halodurans. Kinetic characteristics of sulfate transport in the marine bacteria were similar to those of previously reported nonmarine systems in spite of significant regulatory differences. Sulfate and thiosulfate uptake in P. halodurans responded identically to inhibitors, were coordinately regulated by growth on various sulfur compounds and sulfur starvation, and were mutually competitive inhibitors of transport, suggesting that they were transported by the same mechanism. The affinity of P. halodurans for thiosulfate was much greater than for sulfate.

Assimilatory sulfur metabolism in marine microorganisms: a novel sulfate transport system in Alteromonas luteo-violaceus.

The sulfate transport mechanism of a marine bacterium, Alteromonas luteo-violaceus, was unique among microorganisms in its extremely low affinity for the sulfate analog thiosulfate. Distinguishing characteristics included weak inhibition of sulfate transport by thiosulfate, inability to transport thiosulfate effectively, poor growth using thiosulfate as the sole source of sulfur, and a mild effect of the sulfhydryl reagent para-hydroxymercuribenzoate. In contrast, sulfate transport by a marine pseudomonad, Pseudomonas halodurans, was strongly inhibited by thiosulfate, and para-hydroxymercuribenzoate reversibly but completely blocked sulfate transport.