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Biomedical subjects

R Conrad

Publications and source records attributed to R Conrad.

At least 91 records · Page 5Linked to original sources
PubMed1991

Insertion of part of an intron into the 5' untranslated region of a Caenorhabditis elegans gene converts it into a trans-spliced gene.

In nematodes, the RNA products of some genes are trans-spliced to a 22-nucleotide spliced leader (SL), while the RNA products of other genes are not. In Caenorhabditis elegans, there are two SLs, SL1 and SL2, donated by two distinct small nuclear ribonucleoprotein particles in a process functionally quite similar to nuclear intron removal. We demonstrate here that it is possible to convert a non-trans-spliced gene into a trans-spliced gene by placement of an intron missing only the 5' splice site into the 5' untranslated region. Stable transgenic strains were isolated expressing a gene in which 69 nucleotides of a vit-5 intron, including the 3' splice site, were inserted into the 5' untranslated region of a vit-2/vit-6 fusion gene. The RNA product of this gene was examined by primer extension and PCR amplification. Although the vit-2/vit-6 transgene product is not normally trans-spliced, the majority of transcripts from this altered gene were trans-spliced to SL1. We termed the region of a trans-spliced mRNA precursor between the 5' end and the first 3' splice site an "outron." Our results suggest that if a transcript begins with intronlike sequence followed by a 3' splice site, this alone may constitute an outron and be sufficient to demarcate a transcript as a trans-splice acceptor. These findings leave open the possibility that specific sequences are required to increase the efficiency of trans-splicing.

Animals↗
PubMed1991

elt-1, an embryonically expressed Caenorhabditis elegans gene homologous to the GATA transcription factor family.

The short, asymmetrical DNA sequence to which the vertebrate GATA family of transcription factors binds is present in some Caenorhabditis elegans gene regulatory regions: it is required for activation of the vitellogenin genes and is also found just 5' of the TATA boxes of tra-2 and the msp genes. In vertebrates GATA-1 is specific to erythroid lineages, whereas GATA-2 and GATA-3 are present in multiple tissues. In an effort to identify the trans-acting factors that may recognize this sequence element in C. elegans, we used a degenerate oligonucleotide to clone a C. elegans homolog to this gene. We call this gene elt-1 (erythrocytelike transcription factor). It is single copy and specifies a 1.75-kb mRNA that is present predominantly, if not exclusively, in embryos. The region of elt-1 encoding two zinc fingers is remarkably similar to the DNA-binding domain of the vertebrate GATA-binding proteins. However, outside of the DNA-binding domains the amino acid sequences are quite divergent. Nevertheless, introns are located at identical or nearly identical positions in elt-1 and the mouse GATA-1 gene. In addition, elt-1 mRNA is trans-spliced to the 22-base untranslated leader, SL1. The DNA upstream of the elt-1 TATA box contains eight copies of the GATA recognition sequence within the first 300 bp, suggesting that elt-1 may be autogenously regulated. Our results suggest that the specialized role of GATA-1 in erythroid gene expression was derived after separation of the nematodes and the line that led to the vertebrates, since C. elegans lacks an erythroid lineage.

Amino Acid Sequence↗
PubMed1988

Trial of anonymous versus confidential human immunodeficiency virus testing.

Before December, 1986, all public human immunodeficiency virus (HIV) testing in Oregon was done confidentially (using names). In December, clients were offered the option of either anonymous or confidential services. As judged by questionnaire responses, the availability of anonymity increased overall demand for testing by 50%: 125% for homosexual/bisexual (gay) men, 56% for female prostitutes, 17% for intravenous drug users, and 32% for other clients. The number of gay clients who had tests increased from a mean of 42 per month during the 4 months before anonymity was available to 108 per month during the 4 months after, whereas, at public sites in Colorado or California and private sites in Oregon, the number of gay clients tested did not increase. Twice as many seropositive persons were identified during the 3 1/2 months after anonymity became available (n = 85) as in the 3 1/2 months before (n = 36). Thus, availability of anonymous HIV testing and counselling drew gay men who had not sought services under a confidential testing system.

California↗
PubMed1988

Influence of pH on microbial hydrogen metabolism in diverse sedimentary ecosystems.

Hydrogen transformation kinetic parameters were measured in sediments from anaerobic systems covering a wide range of environmental pH values to assess the influence of pH on hydrogen metabolism. The concentrations of dissolved hydrogen were measured and hydrogen transformation kinetics of the sediments were monitored in the laboratory by monitoring hydrogen consumption progress curves. The hydrogen turnover rate constants (kt) decreased directly as a function of decreasing sediment pH, and the maximum hydrogen uptake velocities (Vmax) varied as a function of pH within each of the trophic states. Conversely, the half-saturation concentrations (Km) were independent of pH. The steady-state hydrogen concentrations were at least 2 orders of magnitude lower than the half-saturation constants for hydrogen uptake. Dissolved hydrogen concentrations were at least fivefold higher in sediments from eutrophic systems than from oligotrophic and dystrophic systems. The rates of hydrogen production determined from the assumption of steady state decreased with sediment pH. These data indicate that progressively lower pH values inhibit microbial hydrogen-producing and -consuming processes within sedimentary ecosystems.

Bacteria, Anaerobic↗
PubMed1988

Prevalence of hepatitis B markers among pregnant Hispanic women in migrant/seasonal work in Oregon.

We screened 303 Hispanic pregnant women who were migrant or seasonal agricultural workers in Oregon for the presence of Hepatitis B serological markers. One carrier was identified (0.3 per cent, 95% confidence interval [CI] .02%, 2.1%). Evidence of previous HB infection was present in 5.3 per cent (16/303) of the women (95% CI 3.2%, 8.6%), rates similar to those for the general US population.

Adolescent↗
PubMed1985

Sulfate-Dependent Interspecies H(2) Transfer between Methanosarcina barkeri and Desulfovibrio vulgaris during Coculture Metabolism of Acetate or Methanol.

We compared the metabolism of methanol and acetate when Methanosarcina barkeri was grown in the presence and absence of Desulfovibrio vulgaris. The sulfate reducer was not able to utilize methanol or acetate as the electron donor for energy metabolism in pure culture, but was able to grow in coculture. Pure cultures of M. barkeri produced up to 10 mumol of H(2) per liter in the culture headspace during growth on acetate or methanol. In coculture with D. vulgaris, the gaseous H(2) concentration was </=2 mumol/liter. The fractions of CO(2) produced from [C]methanol and 2-[C]acetate increased from 0.26 and 0.16, respectively, in pure culture to 0.59 and 0.33, respectively, in coculture. Under these conditions, approximately 42% of the available electron equivalents derived from methanol or acetate were transferred and were utilized by D. vulgaris to reduce approximately 33 mumol of sulfate per 100 mumol of substrate consumed. As a direct consequence, methane formation in cocultures was two-thirds that observed in pure cultures. The addition of 5.0 mM sodium molybdate or exogenous H(2) decreased the effects of D. vulgaris on the metabolism of M. barkeri. An analysis of growth and carbon and electron flow patterns demonstrated that sulfate-dependent interspecies H(2) transfer from M. barkeri to D. vulgaris resulted in less methane production, increased CO(2) formation, and sulfide formation from substrates not directly utilized by the sulfate reducer as electron donors for energy metabolism and growth.

Journal Article↗
PubMed1985

Gas metabolism evidence in support of the juxtaposition of hydrogen-producing and methanogenic bacteria in sewage sludge and lake sediments.

We developed new techniques to measure dissolved H(2) and H(2) consumption kinetics in anoxic ecosystems that were not dependent on headspace measurements or gas transfer-limited experimentation. These H(2) metabolism parameters were then compared with measured methane production rates, and estimates of H(2) production and interspecies H(2) transfer were made. The H(2) pool sizes were 205 and 31 nM in sewage sludge from an anaerobic digestor and in sediments (24 m) from Lake Mendota, respectively. The H(2) turnover rate constants, as determined by using in situ pool sizes and temperatures, were 103 and 31 h for sludge and sediment, respectively. The observed H(2) turnover rate accounted for only 5 to 6% of the expected H(2)-CO(2)-dependent methanogenesis in these ecosystems. Our results are in general agreement with the results reported previously and are used to support the conclusion that most of the H(2)-dependent methanogenesis in these ecosystems occurs as a consequence of direct interspecies H(2) transfer between juxtapositioned microbial associations within flocs or consortia.

Journal Article↗
PubMed1984

Physiological function of hydrogen metabolism during growth of sulfidogenic bacteria on organic substrates.

Desulfovibrio vulgaris Madison and Thermodesulfobacterium commune contained functionally distinct hydrogenase activities, one which exchanged 3H2 into 3H2O and was inhibited by carbon monoxide and a second activity which produced H2 in the presence of CO. Cell suspensions of D. vulgaris used either lactate, pyruvate, or CO as the electron donor for H2 production in the absence of sulfate. Both sulfidogenic species produced and consumed hydrogen as a trace gas during growth on lactate or pyruvate as electron donors and on thiosulfate or sulfate as electron acceptors. Higher initial levels of hydrogen were detected during growth on lactate-sulfate than on pyruvate-sulfate. D. vulgaris but not T. commune also produced and then consumed CO during growth on organic electron donors and sulfate or thiosulfate. High partial pressures of exogenous H2 inhibited growth and substrate consumption when D. vulgaris was cultured on pyruvate alone but not when it was metabolizing pyruvate plus sulfate or lactate plus sulfate. The data are discussed in relation to supporting two different models for the physiological function of H2 metabolism during growth of sulfidogenic bacteria on organic electron donors plus sulfate. A trace H2 transformation model is proposed for control of redox processes during growth on either pyruvate or lactate plus sulfate, and an obligate H2 cycling model is proposed for chemiosmotic energy coupling during growth on CO plus sulfate.

Bacteria↗
PubMed1983

Production and consumption of hydrogen in a eutrophic lake.

The vertical distribution of hydrogen was measured in the Loclat, a eutrophic and holomictic lake near Neuchâtel, Switzerland, before and during summer stratification. H(2) concentrations decreased with depth in the anaerobic hypolimnion and were often below the detection limit (2.5 nl of H(2) liter) in the water adjacent to the lake sediment. H(2) was apparently not released from the lake sediment. The highest H(2) concentrations (>4 mul of H(2) liter) were observed in the aerobic water of the epilimnion and metalimnion. There, the H(2) concentrations changed with time, indicating a turnover of H(2). The H(2) production processes could not be studied in the laboratory since incubation of water samples in light or darkness did not result in H(2) production but rather always in H(2) consumption. The possible role of cyanobacteria and algae for H(2) production is discussed. Aerobic or anaerobic H(2) consumption activities were observed at all depths of the water column, with highest activities in the hypolimnion. Aerobic H(2) consumption activity was insensitive to azide inhibition, but sensitive to heat, mercuric chloride, or cyanide. It was restricted to a particle fraction of 0.2 to 3.0 mum in size, so that it must be due to single bacterial cells. Aerobic hydrogen bacteria, on the other hand, occurred in clusters of >3.0 mum. Therefore, the hydrogen bacteria could not have caused the H(2) consumption in lake water. The aerobic H(2) consumption activity followed Michaelis-Menten kinetics, with a K(m) of 67 nM H(2). This is an exceptionally low value compared with K(m) values of hydrogenases in hydrogen bacteria and other species, but is similar to that for H(2)-decomposing abiontic soil hydrogenases.

Journal Article↗
PubMed1981

Role of carboxydobacteria in consumption of atmospheric carbon monoxide by soil.

The carbon monoxide consumption rates of the carboxydobacteria Pseudomonas (Seliberia) carboxydohydrogena, P. carboxydovorans, and P. carboxydoflava were measured at high (50%) and low (0.5 mul liter) mixing ratios of CO in air. CO was only consumed when the bacteria had been grown under CO-autotrophic conditions. As an exception, P. carboxydoflava consumed CO also after heterotrophic growth on pyruvate. At low cell densities the CO consumption rates measured at low CO mixing ratios were similar in cell suspensions and in mixtures of bacteria in soil. CO consumption observed in natural soil (loess, eolian sand, chernozem) as well as in suspensions or soil mixtures of carboxydobacteria showed Michaelis-Menten kinetics. The K(m) values for CO of the carboxydobacteria (K(m) = 465 to 1,110 mul of CO liter) were much higher than those of the natural soils (K(m) = 5 to 8 mul of CO liter). Considering the difference of the K(m) values and the observed V(max) values, carboxydobacteria cannot contribute significantly to the consumption of atmospheric CO.

Journal Article↗
PubMed1980

Role of microorganisms in the consumption and production of atmospheric carbon monoxide by soil.

Consumption and production of atmospheric CO was measured under field conditions in three different types of soil. CO was consumed by an apparent first-order reaction and produced by an apparent zero-order reaction, resulting in a dynamic equilibrium with the consumption of atmospheric CO as the net reaction. CO consumption was higher in summer than in winter. Laboratory experiments on five different soil types showed that CO consumption was strongly inhibited by the presence of streptomycin or cycloheximide (Actidione), or both. Thus, eucaryotic as well as procaryotic microorganisms were apparently responsible for the observed CO consumption. The aerobic carboxydobacterium Pseudomonas carboxydovorans added to sterile soil was able to utilize the low amounts (ca. 0.7 ppmv) of CO present in laboratory air. CO was consumed by soil under aerobic as well as anaerobic conditions. Anaerobic preincubation of the soil stimulated the anaerobic CO consumption and reduced the aerobic CO consumption. In contrast to CO consumption, CO production was stimulated by autoclaving, by ultraviolet-irradiation, by fumigation with NH(3) or CHCl(3), by treatment with streptomycin or cycloheximide or both, by addition of NaCN, NaN(3), or Na(2)HAsO(4) (or all three) in the presence of glucose under an atmosphere of pure oxygen, or by a drying and rewetting procedure. The consumption of atmospheric CO by soil is a microbial process, but the production of CO is apparently not a metabolic process.

Journal Article↗
PubMed1979

Evaluation of the efficiency of extraction for the quantitative estimation of hydrogen bacteria in soil.

The efficiency of extraction of hydrogen bacteria from soil for plate counting was evaluated by using pure cultures adsorbed to sterilized soil. The utilization of model materials which interact with bacteria by adhesive, capillary or electrostatic forces and the use of extraction fluids with buffering, detergent or chelating activity demonstrated the major importance of capillary forces for the retention of hydrogen bacteria. Utilization of Tris buffer (pH 7.5) as extraction fluid and separation of extracted bacteria from soil particles by sedimentation for 15 min resulted in the highest recovery. A second extraction step including sonication did not increase the efficiency. The extraction efficiency of 8 different strains of hydrogen bacteria adsorbed to 3 different soils demonstrated a high degree of variation wih respect to bacterial strains, but not to soil types. The recovery was inversely related to cell parameters such as size, motility and slime formation.

Adsorption↗