Biomedical subjects

W J Smolenski

Publications and source records attributed to W J Smolenski.

4 recordsLinked to original sources

PubMed1998

Assessment of reductive acetogenesis with indigenous ruminal bacterium populations and Acetitomaculum ruminis.

The objective of this study was to evaluate the role of reductive acetogenesis as an alternative H2 disposal mechanism in the rumen. H2/CO2-supported acetogenic ruminal bacteria were enumerated by using a selective inhibitor of methanogenesis, 2-bromoethanesulfonic acid (BES). Acetogenic bacteria ranged in density from 2.5 x 10(5) cells/ml in beef cows fed a high-forage diet to 75 cells/ml in finishing steers fed a high-grain diet. Negligible endogenous acetogenic activity was demonstrated in incubations containing ruminal contents, NaH13CO3, and 100% H2 gas phase since [U-13C]acetate, as measured by mass spectroscopy, did not accumulate. Enhancement of acetogenesis was observed in these incubations when methanogenesis was inhibited by BES and/or by the addition of an axenic culture of the rumen acetogen Acetitomaculum ruminis 190A4 (10(7) CFU/ml). To assess the relative importance of population density and/or H2 concentration for reductive acetogenesis in ruminal contents, incubations as described above were performed under a 100% N2 gas phase. Both selective inhibition of methanogenesis and A. ruminis 190A4 fortification (>10(5) CFU/ml) were necessary for the detection of reductive acetogenesis under H2-limiting conditions. Under these conditions, H2 accumulated to 4, 800 ppm. In contrast, H2 accumulated to 400 ppm in incubations with active methanogenesis (without BES). These H2 concentrations correlated well with the pure culture H2 threshold concentrations determined for A. ruminis 190A4 (3,830 ppm) and the ruminal methanogen 10-16B (126 ppm). The data demonstrate that ruminal methanogenic bacteria limited reductive acetogenesis by lowering the H2 partial pressure below the level necessary for H2 utilization by A. ruminis 190A4.

Acetic Acid↗

PubMed1989

In vitro total-gas, CH4, H2, volatile fatty acid, and lactate kinetics studies on luminal contents from the small intestine, cecum, and colon of the pig.

Two experiments were conducted to assess differences in fermentative activities of digesta obtained from various regions of the pig gastrointestinal tract. In experiment 1, the contents of small intestines, ceca, and colons of 110-kg pigs were collected, diluted twofold, and incubated for 2 h at 37 degrees C. In experiment 2, colonic samples from 16,100-kg pigs were similarly treated, except that the incubation period was 5 h. Total gas (gas pressure), CH4, H2, lactate, formate, acetate, propionate, butyrate, valerate, and isovalerate were measured in experiment 1. Only the gas variables were measured in experiment 2. Statistically significant differences (P greater than 0.05) were not observed among the gas production rate estimates across the small-intestinal, cecal, and colonic regions in experiment 1. Furthermore, all the small-intestinal samples and half the cecal samples assayed in experiment 1 were nonmethanogenic. The mean methanogenic and total-gas production rate estimates for the colonic samples in experiment 1 were 0.052 ml g of wet contents-1 h-1 and 1.7 ml of total gas g of wet contents-1 h-1, respectively. No differences in the methanogenic rate estimates were detected between the proximal, middle, and distal thirds of the pig colons (P greater than 0.05). The volatile fatty acid and lactate molar percentages measured in experiment 1 were consistent with previously published observations. Hydrogen accumulated to the greatest extent (7 microM on average) in the in vitro incubations of small-intestinal contents, whereas the H2 concentrations ranged from 0.5 to 1 microM for the incubated cecal and colonic samples in experiment 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Biodegradation of cresol isomers in anoxic aquifers.

The biodegradation of o-, m-, and p-cresol was examined in material obtained from a shallow anaerobic alluvial sand aquifer. The cresol isomers were preferentially metabolized, with p-cresol being the most easily degraded. m-Cresol was more persistent than the para-isomer, and o-cresol persisted for over 90 days. Biodegradation of cresol isomers was favored under sulfate-reducing conditions (SRC) compared with that under methanogenic conditions (MC). Slurries that were acclimated to p-cresol metabolism transformed this substrate at 18 and 330 nmol/h per g (dry weight) for MC and SRC, respectively. Inhibition of electron flow to sulfate reduction with 2.0 mM molybdate reduced p-cresol metabolism in incubations containing sulfate. When methanogenesis was blocked with 5 mM bromoethanesulfonic acid in incubations lacking sulfate, p-cresol catabolism was retarded. Under SRC 3.4 mol of sulfate was consumed per mol of p-cresol metabolized. The addition of sulfate to methanogenic incubations stimulated p-cresol degradation. Simultaneous adaptation studies in combination with spectrophotometric and chromatographic analysis of metabolites indicated that p-cresol was oxidized under SRC to p-hydroxybenzoate via the corresponding alcohol and aldehyde. This series of reactions was inhibited under sulfate-limited or aerobic conditions. Therefore, the primary catabolic event for p-cresol decomposition under SRC appears to involve the hydroxylation of the aryl methyl group.

Anaerobiosis↗

PubMed1987

Alternative nonlinear model for estimating second-order rate coefficients for biodegradation.

A modification of the second-order model for biodegradation was derived, applied to an example data set, and shown to be superior for describing the anaerobic biodegradation of p-cresol by an enriched bacterial consortium. The modified model circumvents the no-growth assumption implicit in the use of the second-order rate equation, but still requires the assumption of first-order kinetics over the course of substrate depletion. Violation of the no-growth assumption is particularly important since overestimates of the pseudo-first-order rate coefficient lead to underestimates of the time required for the removal of a xenobiotic chemical from a contaminated environment. Our calculations show that the errors introduced into the pseudo-first-order rate coefficient (and the resulting estimates of the second-order rate coefficient) approach 100% if one doubling occurs in activity over the course of substrate depletion. For an exemplary data set, use of a first-order model resulted in a 100% overestimate of the first-order decay coefficient, which would in turn lead to a corresponding overestimate of the second-order rate coefficient. The modified model we describe is a potential alternative to the pseudo-first-order model for the routine estimation of second-order rate coefficients.

Bacteria, Anaerobic↗