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PubMed2003

The Bacillus subtilis YufLM two-component system regulates the expression of the malate transporters MaeN (YufR) and YflS, and is essential for utilization of malate in minimal medium.

The Gram-positive bacterium Bacillus subtilis has a complete set of enzymes for the tricarboxylic acid (TCA) cycle and can grow aerobically using most of the TCA cycle intermediates (malate, fumarate, succinate and citrate) as a sole carbon source. The B. subtilis genome sequence contains three paralogous two-component regulatory systems, CitST, DctSR and YufLM. CitST and DctSR activate the expression of a transporter of the Mg(2+)-citrate complex (CitM) and a fumarate and succinate transporter (DctP), respectively. These findings prompted an investigation of whether the YufL sensor and its cognate regulator, YufM, play a role in malate uptake. This paper reports that the YufM regulator shows in vitro binding to the promoter region of two malate transporter genes, maeN and yflS, and is responsible for inducing their expression in vivo. It was also found that inactivation of the yufM or maeN genes resulted in bacteria that could not grow in a minimal salts medium containing malate as a sole carbon source, indicating that the induction of the MaeN transporter by the YufM regulator is essential for the utilization of malate as a carbon source. Inactivation of the yufL gene resulted in the constitutive expression of MaeN. This expression was suppressed by reintroduction of the kinase domain of YufL, indicating that the YufL sensor is required for proper signal detection and signalling specificity. The authors propose that a phosphatase activity of YufL plays an important role in the YufLM two-component regulatory system. The studies reported here have revealed that members of a set of paralogous two-component regulatory systems in B. subtilis, CitST, DctSR and YufLM, are involved in a related function--uptake (and metabolism) of the TCA cycle intermediates--but with distinct substrate specificities.

Bacillus subtilis↗
PubMed1989

Anaerobic Carbon Metabolism by the Tricarboxylic Acid Cycle : Evidence for Partial Oxidative and Reductive Pathways during Dark Ammonium Assimilation.

Nitrogen-limited cells of Selenastrum minutum (Naeg.) Collins are able to assimilate NH(4) (+) in the dark under anaerobic conditions. Addition of NH(4) (+) to anaerobic cells results in a threefold increase in tricarboxylic acid cycle (TCAC) CO(2) efflux and an eightfold increase in the rate of anaplerotic carbon fixation via phosphoenolpyruvate carboxylase. Both of these observations are consistent with increased TCAC carbon flow to supply intermediates for amino acid biosynthesis. Addition of H(14)CO(3) (-) to anaerobic cells assimilating NH(4) (+) results in the incorporation of radiolabel into the alpha-carboxyl carbon of glutamic acid. Incorporation of radiolabel into glutamic acid is not simply a short-term phenomenon following NH(4) (+) addition as the specific activity of glutamic acid increases over time. This indicates that this alga is able to maintain partial oxidative TCAC carbon flow while under anoxia to supply alpha-ketoglutarate for glutamate production. During dark aerobic NH(4) (+) assimilation, no radiolabel appears in fumarate or succinate and only a small amount occurs in malate. During anaerobic NH(4) (+) assimilation, these metabolites contain a large proportion of the total radiolabel and radiolabel accumulates in succinate over time. Also, the ratio of dark carbon fixation to NH(4) (+) assimilation is much higher under anaerobic than aerobic conditions. These observations suggest the operation of a partial reductive TCAC from oxaloacetic acid to malate, fumarate, and succinate. Such a pathway might contribute to redox balance in an anaerobic cell maintaining partial oxidative TCAC activity.

Journal Article↗
PubMed1990

A rapid, semi-automated SDS-PAGE identification system for oral anaerobic bacteria.

SDS-polyacrylamide gel electrophoresis is a useful technique in bacterial differentiation and identification. A rapid, semi-automated SDS-PAGE system (Phast System) was assessed for identification of formate-fumarate-requiring, asaccharolytic, Gram-negative oral anaerobes. The system permitted loading, separation and staining of gels within 2 h. Percentage similarities between strains were determined using correlation coefficients and cluster analysis. The protein profiles were sufficiently reproducible provided that distorted profiles were disregarded. Strains were successfully separated into their species, with the exception of Bacteroides ureolyticus NCTC 10939, which appeared to be distinct from other strains of that species. Twenty-nine unidentified formate-fumarate-requiring, sub-gingival plaque strains were suitably clustered with the standard strains as verified by a series of physiological and biochemical tests.

Bacterial Proteins↗
PubMed1990

Effect of positive redox potentials (greater than +400 mV) on the expression of anaerobic respiratory enzymes in Escherichia coli.

The expression of fumarate reductase and other enzymes of anaerobic respiration in Escherichia coli was studied as a function of the redox potential (Eh) in the medium. Redox potentials up to +300 mV allowed full expression of fumarate reductase (frd) genes. Higher values resulted in decreased expression. The relationship between Eh and expression of frd could be approximated by the Nernst equation, assuming a redox couple with a midpoint potential Eo' = +400 mV to 440 mV. At Eh values greater than +510 mV (generated anaerobically by hexacyanoferrate(III] the degree of repression was the same as that obtained by O2. Hexacyanoferrate(III) also caused decreased activities of dimethylsulphoxide (DMSO), nitrite and nitrate reductases. Since expression of these enzymes depends on FNR, the gene activator of anaerobic respiratory genes, it is suggested that the function of FNR is controlled by a redox couple of Eo' = +400 mV to 440 mV.

Anaerobiosis↗
PubMed1992

The Rhizobium leguminosarum FnrN protein is functionally similar to Escherichia coli Fnr and promotes heterologous oxygen-dependent activation of transcription.

An open reading frame from Rhizobium leguminosarum bv. viciae strain VF39, previously identified and found to be similar to Escherichia coli fnr and Rhizobium meliloti fixK (orf240, thereafter called fnrN), was further analysed. Analysis of the expression of an fnrN-lacZ transcriptional fusion revealed that fnrN is preferentially expressed under oxygen limitation. Using R. meliloti fixN-lacZ fusions it was shown that the fnrN gene product only mediates transcriptional activation under microaerobiosis, indicating that the FnrN protein responds, directly or indirectly, to oxygen. Plasmids which expressed fnrN under the control of an E. coli promoter were able to complement an E. coli fnr mutant with respect to anaerobic growth on nitrate but not fumarate, and to promote anaerobic but not aerobic activation of the Fnr-dependent E. coli genes narGHJI, nirB and fdnGHI coding for nitrate reductase, NADH-dependent nitrite reductase and formate dehydrogenase-N, respectively. Fumarate and DMSO reductase activities were not induced by FnrN. The E. coli fnr gene substituted for fnrN in oxygen-regulated transcription of nirB- and fixN-lacZ fusions in R. leguminosarum. The results indicate that Fnr and FnrN are functionally very similar and share a common mode of oxygen-dependent transcriptional activation. From hybridization studies, it appeared that fnrN-like genes are present in a number of different R. leguminosarum strains.

Amino Acid Sequence↗
PubMed1995

Molecular cloning, expression in Streptomyces lividans, and analysis of a gene cluster from Arthrobacter simplex encoding 3-ketosteroid-delta 1-dehydrogenase, 3-ketosteroid-delta 5-isomerase and a hypothetical regulatory protein.

The Arthrobacter simplex gene coding for 3-ketosteroid-delta 1-dehydrogenase, a key enzyme in the degradation of the steroid nucleus, was cloned in Streptomyces lividans. Nucleotide sequence analysis revealed that the gene for 3-ketosteroid-delta 1-dehydrogenase (ksdD) is clustered with at least two more genes possibly involved in steroid metabolism. Upstream of ksdD, we found a gene, ksdR, encoding a hypothetical regulatory protein that shows homologies to KdgR, the negative regulator of pectin biodegradation in Erwinia, and GyIR, the activator for glycerol metabolism in Steptomyces. A helix-turn-helix DNA-binding domain can be predicted at similar positions near the N-terminal of KsdR, KdgR and GyIR. ksdl adjoining downstream to ksdD codes for a protein that has strong similarities to 3-ketosteroid-delta 5-isomerases. The highly conserved Tyr and Asp residues are present in the active-centre motif of the enzyme. The translated ksdD gene product was found to be similar to the 3-ketosteroid-delta 1-dehydrogenase of Pseudomonas testosteroni and to the fumarate reductase of Shewanella putrefaciens. A region highly conserved between the two steroid dehydrogenases can be aligned to the active-centre motif of the fumarate reductase. S. lividans strains carrying the ksdD gene overexpressed 3-ketosteroid-delta 1-dehydrogenase. The expression of 3-ketosteroid-delta 5-isomerase, however, was barely detectable in recombinant S. lividans strains carrying the ksdl gene, or in the parental Arthrobacter strain.

Amino Acid Sequence↗
PubMed1976

Active transport by membrane vesicles from anaerobically grown Escherichia coli energized by electron transfer to ferricyanide and chlorate.

Active transport of amino acids by membrane vesicles from Escherichia coli, grown anaerobically on glucose in the presence of nitrate, can be energized under anaerobic conditions by electron transfer in the nitrate respiration system with formate as electron donor and nitrate as acceptor. A high rate of amino acid transport is also obtained under anaerobic conditions by electron transfer from formate to the nitrate analogue chlorate or to the membrane-impermeable electron acceptor ferricyanide. Electron transfer from formate to nitrate results in the generation of an electrical potential as is indicated by the uptake of the lipophilic cation triphenylmethylphosphonium. Ferricyanide accpets electrons from at least two sites of the nitrate respiration system. One of these sites appears to be nitrate reductase, because cytochrome b, reduced by formate, is completely reoxidized by ferricyanide and glutamate transport energized by formate plus ferricyanide and formate plus nitrate are affected by the same electron transfer inhibitors. A second site of electron transfer to ferricyanide appears to be located prior to nitrate reductase in the nitrate respiration system, since formate is oxidized at a higher rate in the presence of ferricyanide than with nitrate while formate/ferricyanide energizes transport of amino acids at a lower rate than formate/nitrate. Moreover, electron transfer inhibitors block electron transfer from formate to nitrate to a significantly higher extent than from formate to ferricyanide. The effects of irradiation of the membrane vesicles with near ultra-violet light suggest that quinones play an essential role in the electron transfer from formate to nitrate or ferricyanide. Irradiation blocks completely formate-dependent nitrate and ferricyanide reduction and active transport driven by formate/nitrate and formate/ferricyanide, but has hardly any effect on the activity of formate dehydrogenase and on ascorbate/phenazine methosulphate/oxygen-driven transport. Similar effects of ferricyanide have been observed in membrane vesicles from E. coli, grown anaerobically in the presence of fumarate. In these membrane vesicles a high rate of lactose and triphenylmethylphosphonium uptake under anaerobic conditions is obtained by electron transfer from glycerol 1-phosphate to fumarate and also to ferricyanide and evidence has been presented for the involvement of cytochromes in these electron transfers.

Amino Acids↗
PubMed1990

Carbon-13 nuclear magnetic resonance analysis of [1-13C]glucose metabolism in Trypanosoma cruzi. Evidence of the presence of two alanine pools and of two CO2 fixation reactions.

The non-invasive technique of 13C-nuclear magnetic resonance was applied to study glucose metabolism in vivo in Trypanosoma cruzi, the causative agent of American trypanosomiasis (Chagas' disease). It was found that under anaerobic conditions [1-13C]glucose undergoes a glycolytic pathway whose main metabolic products were identified as [3-13C]alanine, [2-13C]succinate and phosphoryl[1-13C]choline; [2-13C]alanine was also a minor metabolite. The addition of 70% 2H2O to the incubation mixture led to the formation of [3-13C, 3-2H]alanine derived from the prior incorporation of 2H+ into pyruvate. The existence of a [3-13C, 3-2H]pyruvate precursor, although not isolated, could be inferred from the formation of [2-13C, 2-2H]succinate in the same experiment. The latter derives from the CO2 fixation reaction on pyruvate or phosphoenolpyruvate to give malate, which is then converted to succinate through the fumarate intermediate step. The presence of [2-13C]alanine must be traced to a randomization of label at the malate-fumarate stage. Both [3-13C, 3-2H]alanine and [2-13C, 2-2H]succinate were excreted from the cells into the supernatant. When the cell pellet was lysed with perchloric acid it released [3-13C]alanine which was devoid of 2H+. Hence, T. cruzi has two alanine pools: one which incorporates 2H+ from the 2H2O present in the medium and excretes alanine into the latter, and another which is impervious to 2H+ exchange. The fixation of CO2 on a C3 precursor was confirmed by incubation of the T. cruzi cells with [1-13C]glucose and sodium [13C]bicarbonate which led to the formation of [1,2-13C2]succinate (Jcc = 51.8 Hz). Incubation with sodium [13C]bicarbonate and [13C]glucose led to the formation of [1-13C]succinate (182.5 ppm) derived from the 13CO2 fixation on the C3 precursor, and of phosphoryl[1-13C]choline (59.39 ppm) which revealed the presence in T. cruzi of a reductive pathway of CO2 which is independent of the CO2 fixation reaction. The formation of phosphoryl[1-13C]choline from [1-13C]glucose should be attributed to 13CO2 liberated from the former by glucose-6-phosphate dehydrogenase.

Alanine↗
PubMed1991

The H(+)-motive and Na(+)-motive respiratory chains in Bacillus FTU subcellular vesicles.

Respiration-dependent pumping of Na+ and H+ into the inside-out subcellular vesicles of alkalotolerant and halotolerant Bacillus FTU grown at alkaline pH was studied. The vesicles were shown to be competent in Na+ and H+ transport coupled to ascorbate oxidation via N,N,N',N'-tetramethyl-p-phenylenediamine or diaminodurene. The uphill Na+ uptake is strongly stimulated by either protonophores or valinomycin, whereas H+ uptake is stimulated by valinomycin and completely inhibited by protonophores. The salt of a penetrating weak base and of the penetrating weak acid, diethylammonium acetate, potentiates the stimulating effect of protonophores on Na+ uptake and abolishes H+ uptake. Na+ transport, supported by ascorbate oxidation, is resistant to 2-heptyl-4-hydroxyquinoline N-oxide, but sensitive to Ag+ and Na+ ionophore, N,N'-dibenzyl-N,N'-diphenyl-1,2-phenylenediacetamide. Micromolar concentrations of cyanide specifically inhibit the H+ uptake but does not affect Na+ uptake. These cyanide concentrations are shown to cause 70% inhibition of respiration, complete reduction of alpha-type cytochromes and partial reduction of c/b-type cytochromes. To inhibit the remaining respiratory activity and Na/ uptake, approximately 100-fold higher cyanide concentrations are necessary. High cyanide concentrations cause some additional increase in absorbance in the region of cytochromes c and/or b. In the presence of a high cyanide concentration, Na+ uptake can be supported by NADH oxidation by fumarate. This Na+ transport is stimulated by protonophores and diethylammonium acetate, being sensitive to very low concentrations of 2-heptyl-4-hydroxyquinoline N-oxide and Ag+. The NADH-fumarate reductase reaction is also found to be competent in H+ uptake, which is inhibited by protonophores and by much higher 2-heptyl-4-hydroxyquinoline N-oxide concentrations, and is resistant to Ag+. It is inferred that Bacillus FTU possesses two respiratory chains: the H(+)-motive and the Na(+)-motive, which strongly differ in their inhibitor sensitivities. Each chain comprises at least two energy-coupling sites which are localized in their initial and terminal segments. It has been indicated that common redox carrier(s) are present in the two chains.

Bacillus↗
PubMed1997

Structure and function of a second gene cluster encoding the formate dehydrogenase of Wolinella succinogenes.

Wolinella succinogenes contains a single formate dehydrogenase, but two gene loci (fdhI and fdhII) code for the subunits of the enzyme. The nucleotide sequence of fdhII is almost identical with that of fdhI in the region comprising fdhEABCD. The sequences of fdhI and fdhII differ in the promotor regions upstream of fdhE. Deletion mutants lacking either fdhI or fdhII synthesize functional formate dehydrogenases, as shown by growth with formate as electron donor and either fumarate or polysulfide as acceptor substrates, and by the presence of the FdhA subunit and of enzyme activity. In the wild-type strain, the fdhI genes appear to be expressed preferentially during growth with formate and fumarate. The six-times greater amount of the enzyme present upon growth with formate and polysulfide is due to the expression of both fdhI and fdhII. The transcription start sites were located 196-bp and 129-bp upstream of the fdhE start codons of fdhI and fdhII, respectively. An apparently single transcript (5.6 kbp) was detected in polysulfide-grown W. succinogenes by Northern-blot analysis, suggesting that the five open reading frames form operons.

Amino Acid Sequence↗
PubMedDate not supplied

Long-term prevention of atrial fibrillation after coronary artery bypass surgery: comparison of quinidine, verapamil, and amiodarone in maintaining sinus rhythm.

AIM OF STUDY: To evaluate the necessity and efficacy of quinidine fumarate, verapimil, or amiodarone prophylaxis for sinus rhythm maintenance in patients who experienced atrial fibrillation after coronary artery bypass surgery. METHODS: Between 1992 and 1995, this prospective, randomized, placebo-controlled study examined 120 patients in whom atrial fibrillation occurred and was restored to sinus rhythm by pharmacological therapy or direct current cardioversion in the immediately postoperative period after coronary artery by-pass surgery. There were no significant differences in perioperative characteristics among the patients, who were randomly separated into four groups in the course of discharge. In group 1 (n = 30), patients did not receive antiarrhythmic drugs. Quinidine fumarate was given in group 2 (n = 30), verapimil in group 3 (n = 30), and amiodarone in group 4 (n = 30). Patients were monitored six times over a 90-day postoperative period by 24-hour Holter monitoring and routine examination. RESULTS: The recurrent atrial fibrillation usually developed within 15 days of discharge. Atrial fibrillation occurred in one patient (3.33%) in group 1, and two each (6.66%) in groups 2, 3, and 4. Atrial fibrillation was asymptomatic and occurred with slow ventricular response in groups 3 and 4. Side effects occurred in 5 patients (16.6%) given quinidine, 1 patient given amiodarone, but in no patient given verapimil. CONCLUSIONS: There were no significant differences in the maintenance of sinus rhythm among the four groups, so we suggest that long-term prevention of atrial fibrillation in patients with coronary artery bypass grafting was not necessary at the postdischarge period.

Aged↗
PubMed1997

Spirochaeta smaragdinae sp. nov., a new mesophilic strictly anaerobic spirochete from an oil field.

An obligately anaerobic spirochete designated strain SEBR 4228T (T = type strain) was isolated from an oil field of Congo, Central Africa. The strain grew optimally with a sodium chloride concentration of 5% (sodium chloride concentration) growth range 1.0-10%) at 37 degrees C (growth temperature range 20-40 degrees C) and pH of 7.0-7.2 (pH growth range pH 5.5-8.0). Strain SEBR 4228T grew on carbohydrates (glucose, fructose, ribose, D-xylose, galactose, mannitol and mannose), glycerol, fumarate, peptides and yeast extract. Yeast extract was required for growth and could not be replaced by vitamins. It reduced thiosulfate and sulfur, to H2S. Glucose was oxidised to lactate, acetate, CO2 and H2S in the presence of thiosulfate but in its absence lactate, ethanol, CO2 and H2 were produced. Fumarate was fermented to acetate and succinate. The G + C content of strain SEBR 4228T was 50%. Strain SEBR 4228T was spiral shaped measuring 5-30 by 0.3-0.5 micron and was motile with a corkscrew-like motion. Electron microscopy revealed the presence of periplasmic flagella in a 1-2-1 arrangement. Strain SEBR 4228T possessed features typical of the members of the genus Spirochaeta. 16S rRNA sequence analysis revealed that it was closely related to Spirochaeta bajacaliforniensis (similarity 98.6%). The lack of DNA homology with S. bajacaliforniensis (38%), together with other phenotypic differences, indicated that strain SEBR 4228T is a new species, which we have designated Spirochaeta smaragdinae. The type strain is SEBR 4228T (= DSM 11293).

DNA, Ribosomal↗
PubMed1999

Fermentative toluene degradation in anaerobic defined syntrophic cocultures.

A syntrophic coculture of a new sulfate-reducing isolate, strain TRM1, with Wolinella succinogenes degraded toluene with either fumarate or NO3- as the terminal electron acceptor. Neither strain TRM1 nor W. succinogenes could metabolise toluene under these conditions in pure culture. Syntrophic degradation was 2-3 times slower than toluene utilisation by strain TRM1 in pure culture with sulfate as electron acceptor. The culture did not produce benzoate or fatty acids like acetate or propionate in detectable amounts. An increase in biomass of the syntrophic toluene-degrading culture was shown in a growth curve with nitrate as the terminal electron acceptor. Both partner organisms were detected microscopically at the end of the growth experiment. Syntrophic degradation of toluene with W. succinogenes and fumarate as the terminal electron acceptor was also demonstrated with the iron reducer Geobacter metallireducens. The results provide the first example of a fermentative oxidation of an aromatic hydrocarbon in a defined coculture.

Biodegradation, Environmental↗
PubMed1988

Iron toxicity in neonatal foals.

Newborn Shetland foals died of acute hepatic failure following oral administration of approximately 16 mg/kg body weight ferrous fumarate. Lesions in these foals were indistinguishable from lesions in foals given an oral digestive inoculant containing ferrous fumarate and were also similar to the syndrome characterised as 'toxic hepatopathy' in foals in the United States in 1983. We conclude that foals are susceptible to toxicity from low doses of iron compounds in the first few days of life. Vitamin E and selenium deficiency may contribute to this susceptibility.

Administration, Oral↗
PubMed2002

Phenotypic susceptibilities to tenofovir in a large panel of clinically derived human immunodeficiency virus type 1 isolates.

Tenofovir is a nucleotide analogue human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) inhibitor, and its oral prodrug, tenofovir disoproxil fumarate, has recently been approved for the treatment of HIV-1 infection in the United States. The objective of this study was to characterize the in vitro susceptibility profiles of a large panel of clinically derived HIV-1 isolates for tenofovir. The distribution of tenofovir susceptibilities in over 1,000 antiretroviral-naive, HIV-1-infected individuals worldwide was determined using the Virco Antivirogram assay. In addition, phenotypic susceptibilities to tenofovir and other RT inhibitors were determined in a panel of nearly 5,000 recombinant HIV-1 clinical isolates from predominantly treatment-experienced patients analyzed as a part of routine drug resistance testing. Greater than 97.5% of isolates from treatment-naive patients had tenofovir susceptibilities <3-fold above those of the wild-type controls by the Antivirogram. The clinically derived panel of 5,000 samples exhibited a broad range of antiretroviral drug susceptibilities, including 69, 43, and 16% having >10-fold-decreased susceptibilities to at least one, two, and three antiretroviral drug classes, respectively. Greater than 88% of these 5,000 clinical isolates were within the threefold susceptibility range for tenofovir, and >99% exhibited <10-fold-reduced susceptibilities to tenofovir. Decreased susceptibility to tenofovir was not directly associated with resistance to other RT inhibitors; r(2) values of log-log linear regression plots of susceptibility to tenofovir versus susceptibility to other RT inhibitors were <0.4. The results suggest that the majority of treatment-naive and treatment-experienced individuals harbor HIV that remains within the normal range of tenofovir susceptibilities and may be susceptible to tenofovir disoproxil fumarate therapy.

Adenine↗
PubMed1986

Growth and Metabolism of Lactic Acid Bacteria during and after Malolactic Fermentation of Wines at Different pH.

Commercially produced red wines were adjusted to pH 3.0, 3.2, 3.5, 3.7, or 4.0 and examined during and after malolactic fermentation for growth of lactic acid bacteria and changes in the concentrations of carbohydrates, organic acids, amino acids, and acetaldehyde. With one exception, Leuconostoc oenos conducted the malolactic fermentation in all wines and was the only species to occur in wines at pH below 3.5. Malolactic fermentation by L. oenos was accompanied by degradation of malic, citric, and fumaric acids and production of lactic and acetic acids. The concentrations of arginine, histidine, and acetaldehyde also decreased at this stage, but the behavior of hexose and pentose sugars was complicated by other factors. Pediococcus parvulus conducted the malolactic fermentation in one wine containing 72 mg of total sulfur dioxide per liter. Fumaric and citric acids were not degraded during this malolactic fermentation, but hexose sugars were metabolized. P. parvulus and species of Lactobacillus grew after malolactic fermentation in wines with pH adjusted above 3.5. This growth was accompanied by the utilization of wine sugars and production of lactic and acetic acids.

Journal Article↗
PubMed1986

Metabolism of Aspartate by Propionibacterium freudenreichii subsp. shermanii: Effect on Lactate Fermentation.

More than 90% of the aspartate in a defined medium was metabolized after lactate exhaustion such that 3 mol of aspartate and 1 mol of propionate were converted to 3 mol of succinate, 3 mol of ammonia, 1 mol of acetate, and 1 mol of CO(2). This pathway was also evident when propionate and aspartate were the substrates in complex medium in the absence of lactate. In complex medium with lactate present, about 70% of the aspartate was metabolized to succinate and ammonia during lactate fermentation, and as a consequence of aspartate metabolism, more lactate was fermented to acetate and CO(2) than was fermented to propionate. The conversion of aspartate to fumarate and ammonia by the enzyme aspartase and subsequent reduction of fumarate to succinate occurred in the five strains of Propionibacterium freudenreichii subsp. shermanii studied. The ability to metabolize aspartate in the presence of lactate appeared to be related to aspartase activity. The specific activity of aspartase increased during and after lactate utilization, and the levels of this enzyme were lower in cells grown in defined medium than levels in those cells grown in complex medium. Under the conditions used, no other amino acids were readily metabolized in the presence of lactate. The possibility that aspartate metabolism by propionibacteria in Swiss cheese has an influence on CO(2) production is discussed.

Journal Article↗
PubMed1989

Reinvestigation of Brevibacterium sp. Strain KY-4313 as a Source of Canthaxanthin.

The hydrocarbon-utilizing Brevibacterium sp. strain KY-4313 was reevaluated for its potential to produce canthaxanthin, a carotenoid pigment of strong commercial interest. Three approaches were used to optimize the canthaxanthin yield from this organism, i.e., the preparation of mutants, the addition of supposedly carotenogenic chemicals to the growth medium, and growth promotion. Following treatment of the parent strain with N-nitrosomethylurea, a presumed mutant was isolated which showed a 32% increase in cellular canthaxanthin content. No effective carotenogenic chemicals were found in connection with hydrocarbon fermentations, in which mainly growth promotion through periodic medium renewal proved conducive to enhanced pigment production. Carotenogenesis could be stimulated in brain heart infusion broth by adding alcohols or retinol. Improved growth in this medium was generally not associated with higher canthaxanthin yields. Both superior growth and pigment levels were obtained in a newly designed medium based on fumaric acid-molasses. The maximum yields of canthaxanthin in shake flasks were (in milligrams per liter) 4.2 (brain heart infusion broth plus propanol-zinc sulfate), 3.6 (hydrocarbon medium), and 9.3 (fumaric acid-molasses), which represent a significant improvement over the originally reported optimal result (1 mg/liter). The corresponding yields of echinenone, the direct precursor of canthaxanthin, were 1.2, 1.6, and 2.3 mg/liter, respectively. Two-liter hydrocarbon batch fermentations involving medium renewal maximally produced 7.2 mg of canthaxanthin and 3.7 mg of echinenone per liter.

Journal Article↗