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.     

Application of continuous oxidative assimilation and endogenous protein synthesis to the treatment of carbohydrate wastes deficient in nitrogen

A synthetic waste (with glucose as carbon source) devoid of a source of nitrogen was purified in a laboratory scale pilot plant by a new modification of the activated sludge process. The process makes use of a separate carbon assimilation (oxidative assimilation) phase and an endogenous phase in which ammonia is added to a portion of the settled sludge and non-nitrogenous products stored in the cells in the assimilation phase are converted to protein. It was found that sludge so treated, when recycled to the assimilation tank, could carry out continuous oxidative assimilation of the waste. Various COD:N ratios were studied. At the highest, 70:1, 90% purificaton efficiency was achieved.     

Endogenous respiration and regulation in a primitive marine fungus

The relationship between the respiration and the presence and utilization of endogenous and exogenous substrates was studied in the non-filamentous obligately marine fungus Thraustochytrium aureum. Using isotopic and manometric methods, it was shown that almost all exogenous glucose is assimilated, whilst almost all the oxygen consumption in the presence of exogenous glucose was due to oxidation of endogenous reserves. In contrast, exogenous glutamate, which cannot serve as the sole carbon source for growth, inhibits respiration of endogenous materials, and is itself rapidly oxidized. The uncoupler 2,4-dinitrophenol stimulates the oxidation of endogenous reserves without affecting the uptake and use of exogenous glucose. These data strongly support the idea of physiologic compartmentation in this organism.     

Comparison of lactose uptake in resting and energized Escherichia coli cells: high rates of respiration inactivate the lac carrier

The transport of lactose by Escherichia coli cells was radically different in the absence and in the presence of an exogenous energy source: in the former case, the time course of lactose accumulation was monotonous; in the latter case, lactose accumulation reached a maximum and then decreased to a final steady-state level lower than that observed in the absence of an energy source. We show that this "overshoot" is the result of a decrease in the influx rate and of an increase in the rate constant of efflux as lactose accumulates. These phenomena were irreversible. The extent of the overshoot was dependent upon the experimental conditions: it was maximal at alkaline pH, for low external potassium concentrations, and for relatively high external lactose concentrations (around or above the KT of uptake). The addition of an energy source to resting E. coli cells resulted in an increase in both the electrochemical gradient of protons and in the rate of respiration. We demonstrate that the overshoot is the result of the latter and unrelated to the former. We observed an irreversible decrease in the membrane potential as lactose accumulated in the presence of an exogenous energy source. We discuss the whole of our data in terms of an irreversible inactivation of the lactose carrier as a result of a possible interaction with the respiratory chain.     

Einfluß des Phasenstatus der Vorkulturzellen auf die Ascosporenbildung von Saccharomyces cerevisiae

Summary Cells from three growth phases were examined for their ability to sporulate: cells from a) phase II (first phase of exponential growth with glucose as carbon source), b) phase III (second lag-phase during adaptation to oxidative metabolism), and c) phase IV (second phase of almost exponential growth with ethanol as carbon source). 1. Cells from phase III showed the best sporulation ability because they reached the highest percentage of asci and also of 4-spored asci. 2. Cells of phase II exhibited the highest and those of phase IV the lowest rate of sporulation (Fig. 3). 3. The longer the cells remained in the presporulation medium the more abbreviated was the time in the sporulation culture before the first asci appeared, and this abbreviation was just equal to the time of elongation in the preculture. This clearly demonstrates the different degree of respiratory adaptation. — After transfer to the sporulation medium O₂-consumption arose to a steep maximum within the first 10 hours followed by medium values which dropped again rapidly at the onset of ascospore formation (Fig. 4). Only during the time of high and medium O₂-consumption there was an increase in dry weight reflecting the assimilation of acetate. In cells of phase II compared with those of phase IV this assimilation of acetate showed the same delay as the onset of sporulation, whereas full capacity of respiration was reached much sooner.     

The Relation of Phosphate Metabolism to Oxidative Assimilation of Acetate by Euglena gracilis var. bacillaris. Effects of 2,4-Dinitrophenol*

SYNOPSIS. Oxidative assimilation of acetate by Euglena gracilis var. bacillaris occurs without appreciable net transfer of inorganic phosphate between cells and medium. Low concentrations of the “uncoupling agent” 2,4-dinitrophenol (2–5 μM, pH 5) stimulate acetate oxidation and inhibit acetate assimilation. These dinitrophenol concentrations have no measurable effect on edogenous respiration. Higher concentrations inhibit respiration on acetate, and still higher concentrations inhibit endogenous respiration. Dinitrophenol concentrations which stimulate acetate oxidation produce no measurable change in the total ATP content of the euglena cells. Higher concentrations (50–100 μM) cause progressive decrease in the ATP content. A hypothetical mechanism is proposed which accounts for the normal, constant oxidation-assimilation ratio for acetate as the result of coupling of oxidative ATP synthesis with assimilatory ATP consumption. The data are consistent with this mechanism if it is additionally assumed that oxidation and assimilation of acetate occur in an intracellular “compartment” separated from other sources and sinks of ATP.     

Inorganic composition and microbial characteristics of methanogenic granular sludge grown in a thermophilic upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket reactor was operated under thermophilic conditions (55° C) for 160 days by feeding a wastewater containing sucrose as the major carbon source. The reactor exhibited a satisfactory performance due to the formation of well-settling granulated sludge, achieving a total organic carbon (TOC) removal of above 80% at an organic loading rate of 30 kg total organic C m^–3 day^–1. Structural and microbial properties of the methanogenic granular sludge were examined using scanning electron microscope X-ray analyses and serum vial activity tests. All the thermophilic granules developed showed a double-layered structure, comprised of a black core portion and a yellowish exterior portion. The interior cope portion contained abundant crystalline precipitates of calcium carbonate. Calcium-bound phosphorus was also present more prominently in the core portion than in the exterior portion. Methanogenic activities of the thermophilic granules both from acetate and from H₂ increased with increasing vial-test temperature in the range of 55–65° C [from 1.43 to 2.36 kg CH₄ chemical oxygen demand (COD) kg volatile suspended solids (VSS)^–1 day^–1 for acetate and from 0.85 to 1.11 kg CH₄ COD kg VSS^–1 day^–1 for H₂]. On the other hand, propionate-utilizing methanogenic activity was independent of vial-test temperature, and was much lower (0.1–0.12 kg CH₄ COD kg VSS^–1 day^–1) than that from either acetate or H₂. Acetate consumption during vial tests was considerably inhibited by the presence of H₂ in the headspace, indicating that a syntrophic association between acetate oxidizers and H₂-utilizing methane-producing bacteria was responsible for some portion of the overall acetate elimination by the theromophilically grown sludge.     

Changes in disulfide bond content of proteins in a yeast strain lacking major sources of NADPH

A yeast mutant lacking the two major cytosolic sources of NADPH, glucose-6-phosphate dehydrogenase (Zwf1p) and NADP+-specific isocitrate dehydrogenase (Idp2p), has been demonstrated to lose viability when shifted to medium with acetate or oleate as the carbon source. This loss in viability was found to correlate with an accumulation of endogenous oxidative by-products of respiration and peroxisomal beta-oxidation. To assess effects on cellular protein of endogenous versus exogenous oxidative stress, a proteomics approach was used to compare disulfide bond-containing proteins in the idp2Deltazwf1Delta strain following shifts to acetate and oleate media with those in the parental strain following similar shifts to media containing hydrogen peroxide. Among prominent disulfide bond-containing proteins were several with known antioxidant functions. These and several other proteins were detected as multiple electrophoretic isoforms, with some isoforms containing disulfide bonds under all conditions and other isoforms exhibiting a redox-sensitive content of disulfide bonds, i.e., in the idp2Deltazwf1Delta strain and in the hydrogen peroxide-challenged parental strain. The disulfide bond content of some isoforms of these proteins was also elevated in the parental strain grown on glucose, possibly suggesting a redirection of NADPH reducing equivalents to support rapid growth. Further examination of protein carbonylation in the idp2Deltazwf1Delta strain shifted to oleate medium also led to identification of common and unique protein targets of endogenous oxidative stress.     

Effect of Co‐Substrates on Aerobic Phenol Degradation by Acclimatized and Non‐acclimatized Enrichment Cultures

Aerobic degradation of 7 mmol/L phenol in the presence of alternative carbon sources (7 mmol/L glucose or acetate or 1–2 mmol/L 2‐chlorophenol) was investigated using non‐acclimatized and acclimatized sewage sludges and enrichment cultures. The substrates represented an intermediate of phenol degradation (acetate), an independent substrate (glucose) or a “precursor‐substrate” of phenol degradation (2‐chlorophenol). Bacteria from sewage sludge, not pre‐adapted to phenol (2 mmol/L), rapidly respired acetate and glucose in the presence of phenol, whereas phenol was only bioconverted to any unknown aromatic metabolite after 24 h. In the presence of phenol and 2‐chlorophenol, no removal of both substances was observed when using the unacclimatized sludge. Sludge that was acclimatized to the degradation of phenol showed an initial preference for easily degradable co‐substrates such as glucose or acetate with only a slow concomitant respiration of phenol. Respiration of phenol increased rapidly after the co‐substrates were depleted. The highest phenol degradation rates were 51.6 mmol/L d, when phenol was the sole carbon substrate. Vice versa, phenol was preferentially respired in the presence of a less easily degradable co‐substrate such as 2‐chlorophenol at a rate of around 7 mmol/L d. Further studies with an enrichment culture that was obtained after 7 successive transfers of phenol‐adapted sludge into mineral medium with phenol as the only carbon source indicated that the acetate and glucose‐degrading capabilities were diminished or almost completely lost. In these enrichment cultures, phenol degradation was not affected by the presence of glucose, but glucose was not degraded. In contrary, the presence of acetate slightly slowed down the phenol degradation rate of the enrichment culture. Growth of the microorganisms apparently occurred at the expense of phenol and acetate respiration. The result of this work may be of practical importance in determining the feeding strategy, which is the key factor for most biological wastewater treatment systems. When acetate was present together with phenol in a wastewater, the phenol degradation rates were influenced by acetate, since acetate was an intermediate of phenol degradation. Glucose as an “independent substrate” was apparently degraded by other bacteria via acetate, and in this way it also influenced the phenol degradation rates. Glucose‐degrading bacteria could be “washed out” from the acclimatized sludge during several transfers into mineral medium with phenol as the sole carbon source. If later on, glucose was added again, it remained undegraded and did not influence phenol degradation. 2‐Chlorophenol degradation also requires other bacteria than phenol degraders.     

Fate of Hydrocarbons During Oily Sludge Disposal in Soil

A 1,280-day laboratory simulation of the “landfarming” process explored the fate in soil of polynuclear aromatics (PNAs) and total extractable hydrocarbon residues originating from the disposal of an oily sludge. In addition to the measurement of CO₂ evolution, periodic analyses of PNAs and hydrocarbons monitored biodegradation activity. The estimation of carbon balance and of soil organic matter assessed the fate of residual hydrocarbons. Seven sludge applications during a 920-day active disposal period were followed by a 360-day inactive “closure” period with no further sludge applications. A burst of CO₂ evolution followed each sludge addition, but substantial amounts of undegraded hydrocarbons remained at the end of the study. Hydrocarbon accumulation did not inhibit biodegradation performance. Conversion of hydrocarbons to CO₂ predominated during active disposal; incorporation into soil organic matter predominated during the closure period. In this sludge, the predominant PNAs were degraded more completely (85%) than total hydrocarbons. Both biodegradation and abiotic losses of three- and four-ring PNAs contributed to this result. Some PNAs with five and six rings were more persistent, but these constituted only a small portion of the PNAs in the sludge. The study confirmed that the microbially mediated processes of mineralization and humification remove sludge hydrocarbons from soils of landfarms with reasonable efficiency.     

Modeling aerobic carbon source degradation processes using titrimetric data and combined respirometric-titrimetric data: experimental data and model structure

Experimental data are presented that resulted from aerobic batch degradation experiments in activated sludge with simple carbon sources (acetate and dextrose) as substrates. Data collection was done using combined respirometric-titrimetric measurements. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber for monitoring the oxygen uptake rate related to substrate degradation. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value by addition of acid and/or base. The experimental data clearly showed that the activated sludge bacteria react with consumption or production of protons during aerobic degradation of the two carbon sources under study. Thus, the cumulative amount of added acid and/or base could serve as a complementary information source on the degradation processes. For acetate, protons were consumed during aerobic degradation, whereas for dextrose protons were produced. For both carbon sources, a linear relationship was found between the amount of carbon source added and the amount of protons consumed (in case of acetate: 0.38 meq/mmol) or produced (in case of dextrose: 1.33 meq/mmol) during substrate degradation. A model taking into account substrate uptake, CO(2) production, and NH(3) uptake for biomass growth is proposed to describe the aerobic degradation of a C(x)H(y)O(z)-type carbon source. Theoretical evaluation of this model for reference parameters showed that the proton effect due to aerobic substrate degradation is a function of the pH of the liquid phase. The proposed model could describe the experimental observations with both carbon sources.     

Cyanide-Insensitive Respiration inSchizophyllum commune

Two mutants of the hymenomyceteSchizophyllum commune, unable to use acetate as the sole carbon source for growth, were isolated. Growth of the mutants on a glucose minimal medium was only slightly inhibited by sodium azide. Genetic analysis revealed mutations in different chromosomal genes in the respective mutants. Both these mutants exhibited a high cyanide-insensitive endogenous respiration. The inhibition of the respiration by 8-hydroxyquinoline showed the mutants to respire predominantly by an alternative respiratory pathway observed in many fungal species, but not in the hymenomycetes so far. An enhanced cyanide-insensitive respiration was also found in a wild-type strain ofSchizophyllum commune grown in the presence of sodium azide.     

Denitrification with endogenous carbon source at low C/N and its effect on P(3HB) accumulation

The objective of the work reported here was to determine whether the ratio of COD/Nox has an impact on poly-beta-hydroxybutyrate (PHB) metabolism in activated sludge. Furthermore, it was tested if the ratio influenced the percentage use of organic compounds present in wastewater, for endogenous respiration, oxidation, accumulation and denitrification. Gas flow rate in SBR reactor was controlled by thermal mass flow controller (TMFC). Constant amount of air entering sequencing batch reactor was automatically adjusted to stable set-point 2mg O2 L(-1). It means that DO concentration in the reactor could change with oxygen uptake. During the filling period and part of the reaction time DO was nearly zero. Feast period of the external substrate availability and famine period of little amount or no external carbon availability were determined. At 23 h of the reaction time, and COD/Nox ratio 8, denitrification took place only during feast period. What was interesting, poly-beta-hydroxybutyrate degradation was observed in the feast period as well. However, at 11h of the reaction time and COD/Nox ratio 37, denitrification occurred in feast and famine period. In the feast period PHB was accumulated and in the famine period was used as the endogenous carbon source. COD consumption to reduce 1mg N-nitrate was ranging from 1.15 to 6.26 depending on carbon source and increased when exogenous and endogenous carbon were used by activated sludge. The increase in PHB content from 0.25 to 0.43 Cmol/Cmol resulted in a double increase in the amount of nitrogen removed due to denitrification was observed.     

Synaptosomal bioenergetics. The role of glycolysis, pyruvate oxidation and responses to hypoglycaemia

The bioenergetic interaction between glycolysis and oxidative phosphorylation in isolated nerve terminals (synaptosomes) from guinea-pig cerebral cortex is characterized. Essentially all synaptosomes contain functioning mitochondria. There is a tight coupling between glycolytic rate and respiration: uncoupler causes a tenfold increase in glycolysis and a sixfold increase in respiration. Synaptosomes contain little endogenous glycolytic substrate and glycolysis is dependent on external glucose. In glucose-free media, or following addition of iodoacetate, synaptosomes continue to respire and to maintain high ATP/ADP ratios. In contrast to glucose, the endogenous substrate can neither maintain high respiration in the presence of uncoupler nor generate ATP in the presence of cyanide. Pyruvate, but not succinate, is an excellent substrate for intact synaptosomes. The in-situ mitochondrial membrane potential (delta psi m) is highly dependent upon the availability of glycolytic or exogenous pyruvate; glucose deprivation causes a 20-mV depolarization, while added pyruvate causes a 6-mV hyperpolarization even in the presence of glucose. Inhibition of pyruvate dehydrogenase by arsenite or pyruvate transport by alpha-cyano-4-hydroxycinnamate has little effect on ATP/ADP ratios; however respiratory capacity is severely restricted. It is concluded that synaptosomes are valuable models for studying the control of mitochondrial substrate supply in situ.     

SPORE GERMINATION AND CARBON METABOLISM IN FUSARIUM SOLANI. II. ENDOGENOUS RESPIRATION IN RELATION TO GERMINATION

Cochrane , V. W., Jean C. Cochrane , C. b . Collins , and F. G. Serafin . (Wesleyan U., Middletown, Conn.) Spore germination and carbon metabolism in Fusarium solani. II. Endogenous respiration in relation to germination. Amer. Jour. Bot. 50(8): 806–814. Illus. 1963.—Endogenous oxygen uptake by ungerminated macroconidia of Fusarium solani f. phaseoli is more than doubled by exogenous ammonium ion and is increased about 7-fold by germination. The respiratory quotient is halved by the provision of ammonia, which has essentially no effect on the endogenous formation of carbon dioxide. Stimulation by azide and 2,4-dinitrophenol suggests that the supply of phosphate acceptors regulates the rate of endogenous respiration. Mercurials poison the endogenous respiration, cyanide accelerates it, and iodoacetate, arsenite, fluoride, and chelating agents have little effect. Respiration is little affected by changes in pH, external phosphate, oxygen concentration, and spore density, within the limits tested. Spore lipid concentration is increased by cultivation in a high-glucose medium, but this variation in lipid content of spores docs not affect the endogenous Qo₂, nor does a high lipid content abolish the requirement for exogenous carbon for germination. Lipid utilization during endogenous respiration accounts for 37% of the loss in dry weight; lipid is also utilized during germination, but such utilization amounts to only about 5% of the carbon requirement. Neither mannitol nor nitrogenous compounds are significant substrates of endogenous respiration. The oxidation of the exogenous substrates tested does not measurably affect the concomitant rate of endogenous respiration. It is proposed that endogenous respiration can contribute to the synthetic processes of spore germination, although quantitatively insufficient to support germination without exogenous carbon. It is also questioned whether the respiratory quotient is an adequate index of the substrate of endogenous respiration.     

Investigation of the dark metabolism of acetate in photoheterotrophically grown cells ofRhodospirillum rubrum

The mechanism of the aerobic dark assimilation of acetate in the photoheterotrophically grown purple nonsulfur bacteriumRhodospirillum rubrum was studied. Both in the light and in the dark, acetate assimilation inRsp. rubrum cells, which lack the glyoxylate pathway, was accompanied by the excretion of glyoxylate into the growth medium. The assimilation of propionate was accompanied by the excretion of pyruvate. Acetate assimilation was found to be stimulated by bicarbonate, pyruvate, the C₄-dicarboxylic acids of the Krebs cycle, and glyoxylate, but not by propionate. These data implied that the citramalate (CM) cycle inRsp. rubrum cells can function as an anaplerotic pathway under aerobic dark conditions. This supposition was confirmed by respiration measurements. The respiration of cells oxidizing acetate depended on the presence of CO₂ in the medium. The fact that the intermediates of the CM cycle (citramalate and mesaconate) markedly inhibited acetate assimilation but had almost no effect on cell respiration indicated that citramalate and mesaconate were intermediates of the acetate assimilation pathway. The inhibition of acetate assimilation and cell respiration by itaconate was due to its inhibitory effect on propionyl-CoA carboxylase, an enzyme of the CM cycle. The addition of 5 mM itaconate to extracts ofRsp. rubrum cells inhibited the activity of this enzyme by 85%. The data obtained suggest that the CM cycle continues to function inRsp. rubrum cells that have been grown anaerobically in the light and then transferred to the dark and incubated aerobically.     

Utilization of 4 Sugars Known to Occur in Activated Sludge by Aspidisca cicada (Ciliata, Hypotrichida); Effect on Division Rate

SYNOPSIS. Indiviluals of the hypotrich Aspidisca cicada (Müller) were separated from activated sludge and grown clonally. Lactose and sucrose increased its division rate; D-glucose and arabinose were inhibitory. All 4 sugars stimulated growth of the bacteria associated with A. cicada. Spectrophotometric detection of acid production showed that A. cicada utilized lactose and sucrose markedly, glucose only slightly, and arabinose not at all. The increased fission rate in the presence of lactose and sucrose is probably caused directly by these sugars providing a carbon source, and indirectly by increasing the supply of food bacteria. Retardation of growth of A. cicada in the presence of glucose or arabinose perhaps results from these sugars somehow making the food bacteria unavailable to A. cicada. Sugars found in activated sludge may inhibit or stimulate growth in populations of A. cicada , frequently one of the dominant Protozoa in activated sludge.     

Phenomenon of transient repression in Escherichia coli

Paigen, Kenneth (Roswell Park Memorial Institute, Buffalo, N.Y.). Phenomenon of transient repression in Escherichia coli. J. Bacteriol. 91:1201-1209. 1966.-A family of mutants has been obtained in Escherichia coli K-12 in which beta-galactosidase is not inducible for approximately one cell generation after the cells are transferred to glucose from other carbon sources. After that period; the enzyme can be induced at the level appropriate to glucose-grown cultures of the parent cells. Among a wide variety of carbon sources, the only one capable of eliciting a state of transient repression is glucose. Conversely, transient repression occurs when cells are transferred to glucose from any of a variety of other carbon sources. The only exceptions to this so far discovered are lactose, gluconate, and xylose. Susceptibility to transient repression in mutants can also be induced in glucose-grown cells by a period of starvation. Mutant cells which have become susceptible to transient repression lose susceptibility in the presence of glucose only when they are under conditions which permit active protein synthesis. The presence of an inducer of beta-galactosidase is not required during this time, nor does pre-induction for beta-galactosidase diminish the susceptibility of mutants. At least two other catabolite repression-sensitive enzymes (galactokinase and tryptophanase) are also sensitive to transient repression, and the two phenomena are probably related. The absolute specificity of glucose and the pattern of response seen after growth in different carbon sources suggest that the endogenous metabolite which produces these repressions is far more readily derived from glucose in metabolism than it is from any other exogenous carbon source.     

Influence of exogenous substrates on the endogenous respiration of Pseudomonas aeruginosa

Gronlund, Audrey F. (University of British Columbia, Vancouver, Canada), and J. J. R. Campbell. Influence of exogenous substrates on the endogenous respiration of Pseudomonas aeruginosa. J. Bacteriol. 91:1577-1581. 1966.-The influence of growth conditions, ammonium ions, and glucose concentration on endogenous respiration in Pseudomonas aeruginosa was determined by measuring C(14)O(2) evolution from uniformly labeled cells that had previously been grown on C(14)-glucose. A 93% suppression of endogenous C(14)O(2) evolution was evident under growth conditions, and a 66% suppression was observed in the presence of excess glucose. Increasing exogenous glucose concentrations supported decreasing levels of endogenous C(14)O(2) evolution. Ammonium ions slightly suppressed endogenous activity and enhanced the decrease in C(14)O(2) release observed with exogenous glucose. In addition, the effect of exogenous glucose, alpha-ketoglutarate, 2-ketogluconate, aspartic acid, and adenosine selectively on both endogenous ribonucleic acid (RNA) and protein oxidation was followed by measuring C(14)O(2) evolution from cells grown with C(14)-uracil or C(14)-proline. The five exogenous substrates examined suppressed endogenous RNA oxidation, and the degree of suppression appeared to be correlated with the amount of oxygen consumption and, hence, energy gained during the oxidation of these substrates. Oxidation of endogenous protein was decreased when cells were incubated with glucose, aspartate, and adenosine, but was increased when alpha-ketoglutarate and 2-ketogluconate were the exogenous substrates. The influence of the oxidizable exogenous compounds appeared to be related, in part, to the ammonium ion requirement imposed upon the cells for assimilation of the individual exogenous substrate.     

Acetyl-CoA synthetase overexpression in Escherichia coli demonstrates more efficient acetate assimilation and lower acetate accumulation: a potential tool in metabolic engineering

The overexpression of acetyl-CoA (CoA) synthetase (ACS) in Escherichia coli showed significant reduction in acetate during glucose fermentation. It also greatly enhanced acetate assimilation when acetate was used as a carbon source. These features are ideal for applications in metabolic engineering. ACS overexpression can be strategically applied to reduce acetate byproduct, recover wasted carbon, and redirect carbon flux toward more favorable pathways. The native acs gene was cloned and overexpressed in E. coli. Studies showed significant effects on acetate production and assimilation in cultures grown in minimal and complex media with glucose or acetate as the carbon source.