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Biomedical subjects

A F Gaudy

Publications and source records attributed to A F Gaudy.

17 recordsLinked to original sources
PubMed1973

Transient response of continuously cultured heterogeneous populations to changes in temperature.

Completely mixed, once-through continuous culture systems of heterogeneous microbial populations of sewage origin were systematically examined for response to changes in reactor temperature. Systems were operated at two dilution rates of 0.125 and 0.25 per h. "Steady state" conditions of the systems were assessed with the reactors operating at 25 C. From this base line, temperature was decreased to as low as 8 C and increased to as high as 57.5 C. Response was assessed in the ensuing transient phase as the system approached a new "steady state." The response was measured by changes in amount and type of carbon source in the reactor effluent as determined by the chemical oxygen demand test, the anthrone test, and gas chromatography. Biological solids concentration and cell composition (protein, carbohydrate, ribonucleic acid and deoxyribonucleic acid) were also determined. These systems responded more favorably to increases than to decreases in temperature. Regardless of the direction of change, the system with the lowest dilution rate (D = 0.125 per h) responded more successfully; i.e., there was less leakage of carbon source in the effluent and less dilute-out of cells during the transient phase.

Bacteria↗
PubMed1971

Kinetic constants for aerobic growth of microbial populations selected with various single compounds and with municipal wastes as substrates.

The general applicability of the Monod relationship between the logarithmic growth rate constant and substrate concentration was studied for heterogeneous populations metabolizing a variety of substrates including concentrated municipal sewage. It was found that growth could be described by the Monod equation, mu = mu(m)/k(s) + s. The kinetic "constants" for heterogeneous populations growing on concentrated sewage were comparable to those found with glucose as substrate.

Acetates↗
PubMed1971

Control of growth rate by initial substrate concentration at values below maximum rate.

The hyperbolic relationship between specific growth rate, mu, and substrate concentration, proposed by Monod and used since as the basis for the theory of steady-state growth in continuous-flow systems, was tested experimentally in batch cultures. Use of a Flavobacterium sp. exhibiting a high saturation constant for growth in glucose minimal medium allowed direct measurement of growth rate and substrate concentration throughout the growth cycle in medium containing a rate-limiting initial concentration of glucose. Specific growth rates were also measured for a wide range of initial glucose concentrations. A plot of specific growth rate versus initial substrate concentration was found to fit the hyperbolic equation. However, the instantaneous relationship between specific growth rate and substrate concentration during growth, which is stated by the equation, was not observed. Well defined exponential growth phases were developed at initial substrate concentrations below that required for support of the maximum exponential growth rate and a constant doubling time was maintained until 50% of the substrate had been used. It is suggested that the external substrate concentration initially present "sets" the specific growth rate by establishing a steady-state internal concentration of substrate, possibly through control of the number of permeation sites.

Culture Media↗
PubMed1969

Control mechanisms operative in a natural microbial population selected for its ability to degrade L-lysine. I. Effect of glucose in batch systems.

A natural microbial population was selected in a medium containing L-lysine as the sole carbon source and ammonia as a nitrogen source. Cells were harvested from a batch-operated fermentor containing lysine and were grown through one transfer on lysine, glucose, or a mixture of lysine and glucose. By comparing the substrate removal rates and enzymatic capabilities of the cells, it was determined that the inducible enzyme system responsible for lysine degradation was subject to catabolic repression. Inhibition of the activity of preformed enzyme(s) played only a minor role. Preinduction by lysine offered only a small degree of protection against repression. The removal of ammonia nitrogen from the system did not overcome the effect of glucose.

Journal Article↗
PubMed1969

Control Mechanisms Operative in a Natural Microbial Population Selected for Its Ability to Degrade L-Lysine. II. Effects of Fructose and Ribose in Batch Systems.

A natural microbial population was acclimated to L-lysine as the sole carbon source when ammonia nitrogen was provided in the medium. Fructose exerted a slight retarding effect upon the metabolic removal of lysine. The response was due to catabolite repression of the inducible enzyme system responsible for lysine degradation. Inhibition of activity of preformed enzymes played no part in the response. Ribose caused a slight increase in the rate of synthesis of lysine-degrading enzymes.

Journal Article↗
PubMed1969

Control Mechanisms Operative in a Natural Microbial Population Selected for Its Ability to Degrade L-Lysine. III. Effects of Carbohydrates in Continuous-Flow Systems Under Shock Load Conditions.

Two naturally selected microbial populations were maintained under continuousflow conditions with glucose or magnesium growth-limiting. The reactors were subjected to shock loads by changing the influent substrate from L-lysine to a mixture of L-lysine and glucose, L-lysine and fructose, or L-lysine and ribose. During the subsequent transient state, the following parameters were examined: lysine chemical oxygen demand (COD), carbohydrate COD, total COD, biological solids concentration, cell protein, enzymatic capability (lysine-degrading enzymes), and the rate of lysine removal. The carbohydrate was then removed from the influent and the same parameters were examined until a new steady state was established. In all cases, glucose and fructose caused a significant repression of the synthesis of lysine-degrading enzymes, resulting in a decrease in the enzymatic capability of the cells. In the carbon-limited reactor, the faster the flow rate, the greater was the repression, whereas, in the magnesium-limited reactor, the slower the flow rate, the greater was the repression. The introduction of ribose into the reactors caused an initial increase in lysine enzymatic capability followed by a slight repression when ribose degradation started.

Journal Article↗
PubMed1968

Regeneration of oxidative assimilation capacity by intracellular conversion of storage products to protein.

Previous studies have shown that the capacity of a heterogeneous microbial population for oxidative assimilation of glucose can be renewed by periodically subjecting the sludge (or a portion of it) to endogenous respiration in the presence of an exogenous source of nitrogen. Further study of this system led to a modification of the activated sludge process for nitrogen-deficient wastes. However, it was not known whether renewal of oxidative assimilation capacity was possible for substrates which required the presence of inducible enzyme(s) or for substrates which were not carbohydrates. Therefore, studies with lactose and acetate as carbon sources were designed. Both carbon sources were removed under conditions of oxidative assimilation, and the storage products (or a portion of these products) were converted into protein when the sludge was subjected to a period of endogenous respiration (with respect to carbon source) in the presence of an exogenous supply of ammonium sulfate. The "regenerated" sludge exhibited a renewed capacity for oxidative assimilation, thereby indicating that requisite inducible enzymes (e.g., beta-galactosidase in the case of lactose; iso-citritase and malate synthetase in the case of acetate) were not diluted out in the endogenous phase to a degree sufficient to hamper renewed oxidative assimilation capacity. The results also indicated that a noncarbohydrate carbon source can be successfully removed from the medium with this process. However, in the case of acetate, the oxidative assimilation capacity after "regeneration" was not fully restored to the initial level.

Journal Article↗
PubMed1968

Continuous oxidative assimilation of acetic Acid and endogenous protein synthesis applicable to treatment of nitrogen-deficient waste waters.

A previous study indicated that the oxidative assimilation capacity of a heterogeneous microbial population for acetic acid did not return to the initial value after a period of endogenous respiration in the presence of ammonium sulfate. In view of this finding it was not possible to recommend fully the use of a continuous oxidative assimilation process for the treatment of nitrogen-deficient waste waters of noncarbohydrate nature. To put the process to a severe test, a laboratory-scale pilot plant study was done. Acetate (1,000 mg/liter) was fed continuously to a completely mixed, aerated reactor vessel, from which the mixed liquor was channeled to a settling basin. The settling basin supernatant fluid was continuously discharged, and a portion of the settled biological sludge was subjected to endogenous respiration in the presence of ammonium sulfate and was recycled to the aeration vessel. Experiments were conducted at three levels of ammonia nitrogen in the endogenous phase. Approximately 90% removal of the carbon source (expressed as chemical oxygen demand, COD) was attained with a low level of supplemental nitrogen (COD/N = 70:1) and a fairly low reactor detention time (4 hr). Based upon these and previous results, it has been concluded that the process shows promise for application to the treatment of a wide variety of nitrogen-deficient industrial wastes.

Journal Article↗
PubMed1962

Studies on Induction and Repression in Activated Sludge Systems.

Both repression and induction of substrate utilization have been the subject of many basic research investigations employing pure cultures. In this investigation these effects were studied using heterogeneous microbial populations prevalent in such biological treatment processes as activated sludge systems. Diauxic substrate removal by activated sludge was observed in a multicomponent medium consisting of glucose and sorbitol. The sludge was acclimated solely to sorbitol; however, the presence of glucose blocked sorbitol removal until glucose was completely utilized. Both diphasic and triphasic oxygen utilization was shown for activated sludges metabolizing multicomponent synthetic wastes consisting of glucose, melibiose, and lactose. It appears from these studies that melibiose utilization was suppressed by the presence of glucose and, although melibiose induced acclimation to lactose, the presence of melibose suppressed lactose utilization. Studies were also conducted using glycogen and starch systems in which it was found that acclimation to either compound conferred immediate acclimation to the other. It was also found that loss of acclimation to lactose was a passive phenomenon and its kinetics could be predicted on the basis of simple diluting out of the enzyme(s) responsible for such acclimation.

Journal Article↗