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R P Griffiths

Publications and source records attributed to R P Griffiths.

14 recordsLinked to original sources
PubMed1999

Effects of storage on measurements of potential microbial activities in stream fine benthic organic matter.

Sample storage can significantly influence measured microbial activities in stream fine benthic organic matter (FBOM), possibly confounding effects of sample variability and short-term changes in activity. Denitrification potential, acetylene reduction and respiration rates, mineralizable N and extractable ammonium concentrations, and beta-glucosidase and phosphatase enzyme activities of FBOM from first-order mountain streams in the western Oregon Cascade Mountains were assayed at various times after collection to determine potential storage effects. Denitrification potential, phosphatase activity, and extractable ammonium remained stable over a minimum of 11 h of storage at 5 degrees C. Mineralizable N concentrations, respiration rates, and beta-glucosidase activity all decreased within 12 h of collection. Results varied for acetylene reduction. Once assay conditions were established, denitrification potential and respiration rates were linear with incubation time. Based on paired t-tests, measures of acetylene reduction, denitrification potential, respiration rate, beta-glucosidase activity, and phosphatase activity were generally similar at a 1-wk interval within the same stream reaches.

Acetylene↗
PubMed1989

Plasmid expression and maintenance during long-term starvation-survival of bacteria in well water.

Strains of enteric bacteria and pseudomonads containing plasmid R388::Tnl721 (Tpr, Tcr) or pRO101 (Hgr, Tcr) were starved for over 250 days in sterile well water to evaluate effects of starvation-survival on plasmid expression and maintenance. Viable populations dropped to between approximately 0.1 and 1% of the initial populations. Escherichia coli(pRO101) and Pseudomonas cepacia(pRO101) lost both viability and plasmid expression at a lower rate than strains containing R388::Tnl721. Three patterns of host-plasmid interaction were detected: (i) no apparent loss of plasmid expression, (ii) loss of plasmid expression on initial recovery with subsequent expression upon resuscitation, and (iii) loss of capability to produce functional plasmid resistance.

Culture Media↗
PubMed1988

Do comparisons of a food characteristic with ideal necessarily involve learning?

Untrained assessors graphically rated the saltiness of plain slices of white bread relative to a personally ideal level of saltiness, with each test session designed to minimize known contextual effects on ratings. Judgements were highly reliable from the first session. However, the mean of the residual variances of individuals' psychophysical functions was approximately halved by the fifth session. To test whether this was an accommodation to the method or to the product, assessors rated the same product by a different procedure in one further session and a different food by the same procedure in a final session. The mean residuals lay in the direction of an accommodation to the method, but this difference proved not to be significant. The initial fall in residuals might indicate some learning about the product which was not adequately tested in the experimental manipulation. Nevertheless, it is clear that the method can be immediately used with high precision by unpractised volunteers.

Adult↗
PubMed1987

Salt and blood pressure: the triangular hypothesis.

If an unselected sample includes individuals whose blood pressure is sensitive to their salt intake and individuals whose blood pressure is not sensitive, then the superposition of these two sub-populations in a scatterplot of individuals' blood pressures against their salt intakes could give a triangular distribution. The non-correlation in the insensitives would obscure the correlation expected in the sensitives. This hypothesis justifies truncation of such data to test for correlation between blood pressure and salt intake among only the individuals in the higher range of blood pressures observed. No criterion of salt sensitivity is needed. The analysis should succeed if salt intake makes a major contribution to hypertension and would be improved if other putative causes were factored out.

Disease Susceptibility↗
PubMed1982

Field observations of methane concentrations and oxidation rates in the southeastern bering sea.

Measurements of methane oxidation rates were made in southeastern Bering Sea water samples with [C]methane. The rate at which CO(2) evolved from samples exposed to one methane concentration was defined as the relative methane oxidation rate. Rate determinations at three methane concentrations were used to estimate methane oxidation kinetics. The rate constant calculated from the kinetics and the observed methane concentration in the same water sample were used to calculate an in situ methane oxidation rate and the turnover time. First-order kinetics were observed in essentially all experiments in which methane oxidation kinetics were measured. Relative methane oxidation rates were greater in waters collected at inshore stations than at the offshore stations and were greater in bottom samples than in surface samples. In most water samples analyzed, there was essentially no radioactivity associated with the cells. The resulting respiration percentages were therefore very high with a mean of >98%. These data suggest that most of the methane was used by the microflora as an energy source and that very little of it was used in biosynthesis. The relative methane oxidation rates were not closely correlated with methane concentrations and did not appear to be linked to either oxygen or dissolved inorganic nitrogen concentrations. However, there was a significant correlation with relative microbial activity. Our data suggest that the methane oxidizers were associated with the general microbial heterotrophic community. Since these organisms did not appear to be using methane as a carbon source, it is unlikely that they have been isolated and identified as methane oxidizers in the past.

Journal Article↗
PubMed1981

Denitrification and nitrogen fixation in alaskan continental shelf sediments.

Rates of nitrogen fixation and denitrification were measured in Alaskan continental shelf sediments. In some regions, rates of nitrogen fixation and denitrification appeared to be equal; in other areas, rates were significantly different. Potential rates of denitrification were found to be limited primarily by the available nitrate substrate. Major regional differences in rates of denitrification were not statistically significant, but significant differences were found for nitrogen fixation rates in different regions of the Alaskan continental shelf. Estimated net losses of nitrogen from Bering Sea sediments were calculated as 1.8 x 10 g of N/yr. Experimental exposure of continental shelf sediments to petroleum hydrocarbons reduced rates of nitrogen fixation and denitrification in some cases but not others. Long-term exposure was necessary before a reduction in nitrogen fixation rates was observed; unamended rates of denitrification but not potential denitrification rates (NO(3) added) were depressed after exposure to hydrocarbons.

Journal Article↗
PubMed1981

Field observations on the acute effect of crude oil on glucose and glutamate uptake in samples collected from arctic and subarctic waters.

The acute effects of crude oil on glucose uptake rates by marine microorganisms were studied in 215 water and 162 sediment samples collected from both arctic and subarctic marine waters. The mean percentage reduction of glucose uptake rates ranged from 37 to 58 in the water samples exposed to crude oil and from 14 to 36 in the sediment samples. Substrate uptake kinetic studies indicated that the observed reductions by microbial populations exposed to crude oil were caused by metabolic inhibition. The effect of crude oil was less in sediments than in the water samples, with the difference being significant at the P < 0.0002 level. With the exception of one sediment study, all of the differences observed in the uptake rates between treated and nontreated samples were statistically significant. A high degree of variability was observed in the degree which glucose and glutamate uptake rates were altered in water samples exposed to crude oil. In some cases, uptake rates were greater in the samples exposed to crude oil. Data on samples collected in Cook Inlet suggested that areas where pelagic microorganisms are most probably chronically exposed to crude oil are also the areas where the effects of crude oil on glucose uptake are the lowest. Two studies indicated that after pelagic populations are exposed to crude oil for several days, the heterotrophic population adjusts to the presence of crude oil.

Journal Article↗
PubMed1981

Long-term effects of crude oil on uptake and respiration of glucose and glutamate in arctic and subarctic marine sediments.

The effects of crude oil on uptake and respiration (mineralization) of glucose and glutamate in marine sediments were investigated. After the sediments were treated with crude oil, they were replaced at or near the collection site by scuba divers. These sediments remained in situ until they were retrieved for analysis. Glucose and glutamate uptake rates were found to decrease, and the percent respired was found to increase in Arctic and subarctic marine sediments that had been exposed to fresh crude oil. These same changes were also observed when "weathered" crude oil was used and when untreated sediments were overlaid with oiled sediments. When the kinetics of glutamate uptake were determined, both the maximum potential uptake rate and the turnover time were significantly affected. A comparison between the proportion of glucose taken into the cells and that respired as CO(2) indicated that crude oil affected biosynthetic mechanisms. A study of sediments that had been exposed to crude oil for at least 5 months showed that glutamate transport into the cells was affected more extensively than biosynthetic mechanisms. In the initial months of exposure, bacterial concentrations and total adenylate concentrations were found to decrease in the presence of crude oil. Our data suggest that secondary productivity in the marine environment could be adversely affected by the presence of crude oil in marine sediments.

Journal Article↗
PubMed1978

Relative microbial activity and bacterial concentrations in water and sediment samples taken in the Beaufort Sea.

A total of 91 water, 8 ice, and 50 sediment samples taken from the southwestern Beaufort Sea were analyzed for relative microbial activity, bacterial cell concentrations, and percentage of respiration (mineralization). These samples were taken during three field-study periods (August to September 1975; April 1976; and August 1976). Both the relative microbial activity and the cell concentrations in water and sediment samples were lower during the April (winter) sampling period than in the August-September (summer) studies. The percentage of respiration of labeled glutamic acid was higher in the winter water samples than in the summer samples. The water samples showed higher percentage of respiration values than did sediment samples. The average maximimum potential rate of glutamic acid uptake was as high or higher than those observed in studies made in more temperate waters. Samples of melted sea ice showed levels of relative microbial activity that were about the same as that found in the associated seawater. When 1:1 mixtures of melted ice and seawater were analyzed for altered microbial activity, little effect could be detected.

Alaska↗
PubMed1977

Comparison between two methods of assaying relative microbial activity in marine environments.

Two methods for determining relative microbial activity in the marine environment were compared. In one method, a single concentration of a labeled substrate was used to calculate rates of substrate utilization; in the other, multiple concentrations of the same substrate (heterotrophic activity method) were used to calculate maximum potential substrate utilization rates. These studies were made on 232 seawater and 79 sediment samples taken from a variety of marine environments. The highest correlations between these two methods were seen in the sediment samples tested. The lowest correlation coerfficient seen in the sediment samples was 0.90, and the highest was 0.98. In seawater samples (six studies), the lowest correlation coefficient was 0.77 and the highest was 0.95. The correlation between these two methods was also substrate concentration dependent. Higher correlation coefficients were observed when higher substrate concentrations were used. Under certain conditions, these two methods appear to be comparable for estimating relative levels of microbial activity in the marine environment.

Antarctic Regions↗
PubMed1973

Applicability of the reverse-flow filter technique to marine microbial studies.

The use of the reverse-flow filtration technique to quantitatively concentrate marine bacteria was evaluated using both a pure culture and seawater samples. Our data indicate that the cells are altered during the filtration procedure and that a significant and inconsistent number of cells are lost on the membrane filter. The results obtained indicate that data on marine bacteria concentrated in this manner should be interpreted with caution.

Bacteriological Techniques↗