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Geology topics

Charles W. Culbertson

Publications and source records attributed to Charles W. Culbertson.

26 records · Page 2Linked to original sources
USGS2002

Distribution, production, and ecophysiology of Picocystis strain ML in Mono Lake, California

A recently described unicellular chlorophytic alga isolated from meromictic Mono Lake, California, occupies a niche that spans two environments: the upper oxic mixolimnion and the deeper anoxic and highly reducing monimolimnion. This organism, Picocystis sp. strain ML, accounts for nearly 25% of the primary production during the winter bloom and more than 50% at other times of the year. In incubations, it is heavily grazed by the brine shrimp, Artemia monica. We assessed growth and photosynthetic parameters over broad ranges of irradiance, salinity, and pH and under oxic and anoxic conditions. Picocystis appears to be particularly adapted to low irradiance; we observed an order of magnitude increase in the cellular pigment concentrations, as well as marked increases in cellspecific photosynthetic parameters for cells acclimated to low-growth irradiance. Growth rates of 0.3–1.5 d21 were observed over a salinity range of 0–260‰ and a pH range of 4–12, with maximal growth at ;50 mmol photons m22 s21 , 40‰, and pH 6–10. Growth and oxygenic photosynthesis were observed under anoxic conditions at rates comparable to those measured under oxic conditions. The ability of the organism to acclimate and grow under such a broad range of environmental conditions makes it an important component of the Mono Lake ecosystem and likely contributes to its dominance of the monimolimnion/mixolimnion interface.

California↗
USGS1996

Dimethylsulfoniopropionate as a potential methanogenic substrate in Mono Lake sediments

A high concentration of dimethylsulfoniopropionate (DMSP) was found in the water column (0.1–1.8 µM particulate plus dissolved) of Mono Lake, CA, an alkaline, hypersaline waterbody. The dense Artemia monica population contained high levels of DMSP (1.7–2.5 mmol.g -1 wet weight), presumably as an osmolyte. Death of these brine shrimp caused accumulation of DMSP along the shoreline of the lake, where concentrations peaked at 7–13 jumol.cm -3 sediment. DMSP was also associated with the phototrophic microbial population in microbial mats close to the shoreline. Chemical hydrolysis of DMSP caused by the high pH value of the water (9.7–10.0) competed with biological consumption. Flux chamber experiments suggested that part of the dimethylsulfide (DMS) generated by hydrolysis escaped to the atmosphere. Vertical profiles of DMSP and DMS in the sediment correlated well. Methane and DMS also had similar distributions. Additional inhibitor studies showed that a major biological sink for DMS(P) is methanogenesis, although monooxygenase-containing bacteria also contributed to its consumption.

Book chapter↗
USGS1994

Isolation, growth, and metabolism of an obligately anaerobic, selenate- respiring bacterium, strain SES-3

A gram-negative, strictly anaerobic, motile vibrio was isolated from a selenate-respiring enrichment culture. The isolate, designated strain SES-3, grew by coupling the oxidation of lactate to acetate plus CO 2 with the concomitant reduction of selenate to selenite or of nitrate to ammonium. No growth was observed on sulfate or selenite, but cell suspensions readily reduced selenite to elemental selenium (Se 0 ). Hence, SES-3 can carry out a complete reduction of selenate to Se 0 . Washed cell suspensions of selenate-grown cells did not reduce nitrate, and nitrate-grown cells did not reduce selenate, indicating that these reductions are achieved by separate inducible enzyme systems. However, both nitrate-grown and selenate-grown cells have a constitutive ability to reduce selenite or nitrite. The oxidation of [ 14 C]lactate to 14 CO 2 coupled to the reduction of selenate or nitrate by cell suspensions was inhibited by CCCP (carbonyl cyanide m -chlorophenylhydrazone), cyanide, and azide. High concentrations of selenite (5 mM) were readily reduced to Se 0 by selenate-grown cells, but selenite appeared to block the synthesis of pyruvate dehydrogenase. Tracer experiments with [ 75 Se]selenite indicated that cell suspensions could achieve a rapid and quantitative reduction of selenite to Se 0 . This reduction was totally inhibited by sulfite, partially inhibited by selenate or nitrite, but unaffected by sulfate or nitrate. Cell suspensions could reduce thiosulfate, but not sulfite, to sulfide. These results suggest that reduction of selenite to Se 0 may proceed, in part, by some of the components of a dissimilatory system for sulfur oxyanions.

Nevada↗
USGS1992

Importance of methane-oxidizing bacteria in the methane budget as revealed by the use of a specific inhibitor

METHANE is a greenhouse gas whose concentration in the atmosphere is increasing . Much of this methane is derived from the metabolism of methane-generating (methanogenic) bacteria and over the past two decades much has been learned about the ecology of methanogens; specific inhibitors of methanogenesis, such as 2-bromoethanesulphonic acid, have proved useful in this regard . In contrast, although much is known about the biochemistry of methane-oxidizing (methanotrophic) bacteria , ecological investigations have been hampered by the lack of an analogous specific inhibitor . Methanotrophs limit the flux of methane to the atmosphere from sediments and consume atmospheric methane , but the quantitative importance of methanotrophy in the global methane budget is not well known . Methylfluoride (CH 3 F) is known to inhibit oxygen consumption by Methylococcus capsu-latus , and to inhibit the oxidation of 14 CH 4 to 14 CO 2 by endosymbionts in mussel gill tissues . Here we report that methylfluoride (MF) inhibits the oxidation of methane by methane monooxy-genase, and by using methylfluoride in field investigations, we find that methanotrophic bacteria can consume more than 90% of the methane potentially available.

Nature↗
USGS1989

Selenate reduction to elemental selenium by anaerobic bacteria in sediments and culture: Biogeochemical significance of a novel, sulfate-independent respiration

Interstitial water profiles of SeO 4 2− , SeO 3 2− , SO 4 2− , and Cl − in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO 4 2− occurred under anaerobic conditions, was more rapid with H 2 or acetate, and was inhibited by O 2 , NO 3 − , MnO 2 , or autoclaving but not by SO 4 2− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO 2 . A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters.

California↗
USGS1984

Denitrification in San Francisco Bay intertidal sediments

The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO 3 − + NO 2 − concentrations (≤26 μM) were below the apparent K m (50 μM) for nitrate. During the rainy season, when ambient NO 3 − + NO 2 − concentrations were higher (37 to 89 μM), an accurate estimate of the K m could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N 2 O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N 2 O in the presence of C 2 H 2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N 2 O loss was caused by incomplete blockage of N 2 O reductase by C 2 H 2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N 2 m −2 h −1 (for undisturbed sediments) to 17 to 280 μmol of N 2 m −2 h −1 (for shaken sediment slurries).

California↗
USGS1981

Anaerobic oxidation of acetylene by estuarine sediments and enrichment cultures

Acetylene disappeared from the gas phase of anaerobically incubated estuarine sediment slurries, and loss was accompanied by increased levels of carbon dioxide. Acetylene loss was inhibited by chloramphenicol, air, and autoclaving. Addition of 14 C 2 H 2 to slurries resulted in the formation of 14 CO 2 and the transient appearance of 14 C-soluble intermediates, of which acetate was a major component. Acetylene oxidation stimulated sulfate reduction; however, sulfate reduction was not required for the loss of C 2 H 2 to occur. Enrichment cultures were obtained which grew anaerobically at the expense of C 2 H 2 .

California↗