Microbial metabolism of amino alcohols. Aminoacetone metabolism via 1-aminopropan-2-ol in Pseudomonas sp. N.C.I.B. 8858

1. Pseudomonas sp. N.C.I.B. 8858 grew well on d- and l-1-aminopropan-2-ol and on aminoacetone. 2. Cell-free extracts possessed high activities of inducibly formed l-1-aminopropan-2-ol-NAD(+) oxidoreductase, amino alcohol-ATP phosphotransferase, dl-1-aminopropan-2-ol O-phosphate phospho-lyase and aldehyde-NAD(+) oxidoreductase, but no 1-aminopropan-2-ol racemase or d-1-aminopropan-2-ol-NAD(+) oxidoreductase. 3. The amino alcohol kinase (activated by ADP) was non-stereospecific towards 1-aminopropan-2-ol and was one-third as active with ethanolamine. The phospho-lyase was active with l- and d-1-aminopropan-2-ol O-phosphate, but ethanolamine O-phosphate was only one-tenth as active as its higher homologues. The purified aldehyde dehydrogenase was active with propionaldehyde, acetaldehyde and also with methylglyoxal. The previously observed 2-oxo aldehyde dehydrogenase activity was considered to be due to the broadly specific aldehyde dehydrogenase. 4. Mutants of Pseudomonas sp. N.C.I.B. 8858 deficient in 1-aminopropan-2-ol kinase, 1-aminopropan-2-ol O-phosphate phospho-lyase, aldehyde dehydrogenase or an enzyme involved in propionate metabolism were incapable of growth on aminoacetone or 1-aminopropan-2-ol as carbon source, although all except the kinase- or phospho-lyasedeficient mutants could use these compounds and ethanolamine as nitrogen sources. The aldehyde dehydrogenase-deficient mutants produced copious amounts of propionaldehyde and acetaldehyde during growth on the corresponding amino alcohols. 5. The path of aminoacetone metabolism in Pseudomonas sp. N.C.I.B. 8858 was concluded to involve l-1-aminopropan-2-ol, the O-phosphate ester of this compound, propionaldehyde and propionate as obligatory intermediates. d-1-Aminopropan-2-ol was metabolized by the same route as the l-isomer, gratuitously inducing formation of the stereospecific l-1-aminopropan-2-ol dehydrogenase. 6. Extracts of the pseudomonad grown with ethanolamine as the nitrogen source were devoid of 1-aminopropan-2-ol dehydrogenase, the kinase and the phospho-lyase, but exhibited cobamide coenzyme-dependent deaminase activity. Mutants deficient in kinase or phospho-lyase (deaminating) grew well on ethanolamine as the nitrogen source. Ethanolamine deaminase was inactive with, but inhibited by, 1-aminopropan-2-ol.     

Microbial metabolism of amino alcohols. Metabolism of ethanolamine and 1-aminopropan-2-ol in species of Erwinia and the roles of amino alcohol kinase and amino alcohol O-phosphate phospho-lyase in aldehyde formation

1. Growth of Erwinia carotovora N.C.P.P.B. 1280 on media containing 1-aminopropan-2-ol compounds or ethanolamine as the sole N source resulted in the excretion of propionaldehyde or acetaldehyde respectively. The inclusion of (NH(4))(2)SO(4) in media prevented aldehyde formation. 2. Growth, microrespirometric and enzymic evidence implicated amino alcohol O-phosphates as aldehyde precursors. An inducibly formed ATP-amino alcohol phosphotransferase was partially purified and found to be markedly stimulated by ADP, unaffected by NH(4) (+) ions and more active with ethanolamine than with 1-aminopropan-2-ol compounds. Amino alcohol O-phosphates were deaminated by an inducible phospho-lyase to give the corresponding aldehydes. This enzyme, separated from the kinase during purification, was more active with ethanolamine O-phosphate than with 1-aminopropan-2-ol O-phosphates. Activity of the phospho-lyase was unaffected by a number of possible effectors, including NH(4) (+) ions, but its formation was repressed by the addition of (NH(4))(2)SO(4) to growth media. 3. E. carotovora was unable to grow with ethanolamine or 1-aminopropan-2-ol compounds as sources of C, the production of aldehydes during utilization as N sources being attributable to the inability of the microbe to synthesize aldehyde dehydrogenase. 4. Of seven additional strains of Erwinia examined similar results were obtained only with Erwinia ananas (N.C.P.P.B. 441) and Erwinia milletiae (N.C.P.P.B. 955).     

Microbial metabolism of amino ketones: l-1-Aminopropan-2-ol dehydrogenase and l-threonine dehydrogenase in Escherichia coli

1. A wide range of intermediary metabolites and substrate analogues have no effect on the oxidation of dl-1-aminopropan-2-ol to aminoacetone by washed-cell suspensions of Escherichia coli. Only dl-2-hydroxy-2-phenylethylamine, dl-1,3-diaminopropan-2-ol, dl-serine and l-1-(3,4-dihydroxyphenyl)-2-aminoethanol act as inhibitors. 2. Dialysed cell-free extracts of E. coli exhibit an NAD(+)-dependent dl-1-aminopropan-2-ol-dehydrogenase activity of approx. 8mmumoles of aminoacetone formed/mg. of protein/min. at the pH optimum of approx. 10. The K(m) values for the coenzyme and dl-amino alcohol are approx. 0.4 and 10.0mm respectively. A smaller peak of activity occurs at pH7.0-7.2, the K(m) for NAD(+) at pH7 being approx. 0.05mm. 3. Enzyme activity in cell-free extracts is inhibited by dl-2-hydroxy-2-phenylethylamine, dl-1-aminopropane-2,3-diol and dl-serine. dl-Phenylserine and dl-1-aminobutan-2-ol are oxidized to compounds reacting as amino ketones. 4. In fresh cell-free extracts l(+)-1-aminopropan-2-ol preparations are oxidized more rapidly than racemic or laevo-rotatory material, the d(-)-enantiomorph appearing to act as a competitive inhibitor. The K(m) for l(+)-1-aminopropan-2-ol appears to be approx. 1.5mm when highly resolved substrate preparations are used, either in the free base form or as the l(+)-tartrate salt. 5. l(+)-1-Aminopropan-2-ol dehydrogenase is a labile enzyme, and in appropriately treated extracts activity towards the d-enantiomorph is detectable and relatively higher than that towards the l-enantiomorph. 6. Optimum activity of l-threonine-dehydrogenase in cell-free extracts is exhibited at pH9.6 in the presence of NAD(+). The K(m) values for coenzyme and amino acid substrate are approx. 0.08 and 5.0mm respectively. This enzyme is distinct from 1-aminopropan-2-ol dehydrogenases on the basis of kinetic evidence, and the separation of activities by gel filtration. 7. Both l-threonine and dl-1-aminopropan-2-ol dehydrogenases are markedly inhibited by 8-hydroxyquinoline and p-chloromercuribenzoate, but only slightly by other chelating and thiol reagents. 8. E. coli is incapable of growth on simple synthetic media, containing a variety of carbon sources, when dl-1-aminopropan-2-ol is supplied as the sole source of nitrogen. It appears unlikely that the micro-organism can deaminate aminoacetone. 9. The metabolic roles of l-threonine dehydrogenase, aminoacetone and 1-aminopropan-2-ol dehydrogenases are discussed.     

Microbial metabolism of amino ketones. Aminoacetone formation from 1-aminopropan-2-ol by a dehydrogenase in Escherichia coli

1. Washed-cell suspensions of Escherichia coli, incubated at the optimum pH of 6.4 and with a saturating substrate concentration of approx. 10mm, convert dl-1-aminopropan-2-ol into aminoacetone at a rate of approx. 4.0mmumoles/mg. dry wt. of cells/min. at 30 degrees . 2. Mg(2+), Mn(2+), Co(2+), Zn(2+), Ca(2+), K(+) and NH(4) (+), as sulphates, and EDTA have no effect on this rate, although Cu(2+) inhibits and Fe(2+) activates to some extent. 3. Conditions of growth markedly affect the rate of aminoacetone production by cell suspensions. 4. Dialysed cell-free extracts of E. coli exhibit 1-aminopropan-2-ol-dehydrogenase activity, the enzyme having optimum activity at pH7.0, a requirement for NAD(+) and K(+), and a K(m) for the amino alcohol substrate of 0.8mm, calculated for a single enantiomorph. 5. Under optimum conditions 1-aminopropan-2-ol dehydrogenase forms aminoacetone at rate of approx. 3.0mmumoles/mg. of protein/min. at 37 degrees . The enzyme is only slightly inhibited by dl-3-hydroxybutyrate and dl-2-hydroxy-2-phenylethyl-amine. 6. l-Threonine-dehydrogenase activity is exhibited by both whole cells and cell-free extracts. Whole cells produce aminoacetone from l-threonine more slowly than they do from dl-1-aminopropan-2-ol, whereas the situation is reversed in cell-free extracts. Both kinetic evidence, and the fact that synthesis of 1-aminopropan-2-ol dehydrogenase, but not of threonine dehydrogenase, is repressed by compounds such as glucose and pyruvate, provide evidence that the amino alcohol is oxidized by a specific enyme. 7. The metabolic role of 1-aminopropan-2-ol dehydrogenase is discussed.     

Microbial metabolism of amino alcohols. Purification and properties of coenzyme B12-dependent ethanolamine ammonia-lysae of Escherichia coli

1. The 120-fold purification of ethanolamine ammonia-lyase from Escherichia coli extracts, to apparent homogeneity, is described. Ethanolamine, dithiothreitol, glycerol and KCl protected the apoenzyme from inactivation. 2. At the optimum pH7.5, K(m) values for ethanolamine and coenzyme B(12) were 44mum and 0.42mum respectively. The K(m) for ethanolamine was markedly affected by pH, transitions occurring at pH7.0 and 8.35. 3. The enzyme was specific for ethanolamine as substrate, none of the 18 analogues tested being active. l-2-Aminopropan-l-ol (K(i) 0.86mum), dl-1-aminopropan-2-ol (K(i) 2.2mum) and dl-1,3-diaminopropan-2-ol (K(i) 88.0mum) inhibited competitively. 4. Enzyme activity was inhibited, irreversibly and non-competitively, by the coenzyme analogues methylcobalamin (K(i) 1.4nm), hydroxocobalamin (K(i) 2.1nm) and cyanocobalamin (K(i) 4.8nm). 5. Iodoacetamide inhibited in the absence of ethanolamine, but only slightly in its presence. p-Hydroxymercuribenzoate inhibited markedly even in the presence of ethanolamine. Dithiothreitol and 2-mercaptoethanol (less effectively) restored activity to the enzyme dialysed against buffer containing ethanolamine. 6. Although K(+) ions stabilized the enzyme during dialysis or storage, they were not necessary for activity. 7. Gel filtration showed the enzyme to be of high molecular weight, ultracentrifugal studies giving s(20,w) of 16.4 and an estimated mol.wt. 560400. The isoelectric point for the apoenzyme was approx. pH5.0. inhibited enzyme activity at concentrations above 1m (95% inhibition at 3m) and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis indicated protein subunits of mol.wt. 61400. 8. Immunological studies showed that the E.coli enzyme was closely related to those of other enterobacteria, but only distantly to that of Clostridium sp. A double precipitin band suggested that the apoenzyme may be made up of two protein components.     

The phosphorylation and subsequent metabolism of 1-aminopropan-2-ol

Rat liver mitochondria contain an apparently substrate-specific 1-aminopropan-2-ol kinase activity. Indirect evidence also indicates the presence of a phosphoryl-1-aminopropan-2-ol cytidylyl transferase activity. A possible role for these two enzymes in the incorporation of 1-aminopropan-2-ol as a phospholipid base is considered in the light of this and other data.     

Effects of analogues of ethanolamine and choline on phospholipid metabolism in rat hepatocytes

1. Analogues of ethanolamine and choline were incubated with different labelled precursors of phospholipids and isolated hepatocytes and the effects on phospholipid synthesis were studied. 2. 2-Aminopropan-1-ol and 2-aminobutan-1-ol were the most efficient inhibitors of [(14)C]ethanolamine incorporation into phospholipids, whereas the incorporation of [(3)H]choline was inhibited most extensively by NN-diethylethanolamine and NN-dimethylethanolamine. 3. When the analogues were incubated with [(3)H]glycerol and hepatocytes, the appearance of (3)H in unnatural phospholipids indicated that they were incorporated, at least in part, via CDP-derivatives. The distribution of [(3)H]glycerol among molecular species of phospholipids containing 2-aminopropan-1-ol and 1-aminopropan-2-ol was the same as in phosphatidylethanolamine. In other phospholipid analogues the distribution of (3)H was more similar to that in phosphatidylcholine. 4. NN-Diethylethanolamine stimulated both the conversion of phosphatidylethanolamine into phosphatidylcholine and the incorporation of [Me-(14)C]methionine into phospholipids. Other N-alkyl- or NN-dialkyl-ethanolamines also stimulated [(14)C]methionine incorporation, but inhibited the conversion of phosphatidylethanolamine into phosphatidylcholine. This indicates that phosphatidyl-NN-diethylethanolamine is a poor methyl acceptor, in contrast with other N-alkylated phosphatidylethanolamines. 5. These results on the regulation of phospholipid metabolism in intact cells are discussed with respect to the possible control points. They also provide guidelines for future experiments on the manipulation of phospholipid polar-headgroup composition in primary cultures of hepatocytes.     

The metabolism of nitrilotriacetate by a pseudomonad

1. An organism that grows on nitrilotriacetate as sole source of carbon and energy was isolated in pure culture and was identified as a pseudomonad. 2. Cell-free extracts of the nitrilotriacetate-grown pseudomonad contain an enzyme that catalyses the NADH-and O(2)-dependent oxidation of nitrilotriacetate to iminodiacetate and glyoxalate. This enzyme is absent from extracts of glucose-grown cells. 3. Compared with growth on glucose, growth on nitrilotriacetate results in increased activities of enzymes of glycine and serine metabolism, namely serine hydroxymethyltransferase, glycine decarboxylase, serine-oxaloacetate aminotransferase and hydroxypyruvate reductase. 4. Cell-free extracts of the nitrilotriacetate-grown organism contain the enzyme glyoxalate carboligase and, when supplemented with NADH, Mg(2+) and thiamin pyrophosphate, can catalyse the anaerobic conversion of glyoxalate into glycerate. 5. These results are incorporated in a scheme which shows the oxidative metabolism of nitrilotriacetate by the successive removal of C(2) units to form 2mol of glyoxalate and 1mol of glycine per mol of nitrilotriacetate degraded. The glyoxalate and glycine are then both metabolized to glycerate by separate pathways, via tartronic semialdehyde and serine respectively. The role of this scheme in the growth of the organism on nitrilotriacetate is discussed.     

Utilization of l-threonine by a species of Arthrobacter. A novel catabolic role for `aminoacetone synthase''

1. A species of Arthrobacter (designated Arthrobacter 9759) was isolated from soil by its ability to grow aerobically on l-threonine as sole source of carbon atoms, nitrogen atoms and energy; the organism also grew well on other sources of carbon atoms including glycine, but no growth was obtainable on aminoacetone or dl-1-aminopropan-2-ol. 2. During growth on threonine, (14)C from l-[U-(14)C]threonine was rapidly incorporated into glycine and citrate, and thereafter into serine, alanine, aspartate and glutamate. 3. With extracts of threonine-grown cells supplied with l-[U-(14)C]threonine, evidence was obtained of the NAD and CoA-dependent catabolism of l-threonine to produce acetyl-CoA plus glycine. Short-term incorporation studies in which [2-(14)C]acetate and [2-(14)C]glycine were supplied (a) to cultures growing on threonine, and (b) to extracts of threonine-grown cells, showed that the acetyl-CoA was metabolized via the tricarboxylic acid cycle and glyoxylate cycle whereas the glycine was converted into pyruvate via the folate-dependent ;serine pathway'. 4. The threonine-grown organism contained ;biosynthetic' threonine dehydratase and a potent NAD-linked l-threonine dehydrogenase but possessed no l-threonine aldolase activity. 5. Evidence was obtained that the acetyl-CoA and glycine produced from l-threonine had their immediate origin in the alpha-amino-beta-oxobutyrate formed by the threonine dehydrogenase; the CoA-dependent cleavage of this compound was catalysed by an alpha-amino-beta-oxobutyrate CoA-ligase, which was identified with ;aminoacetone synthase'. A continuous spectrophotometric assay of this enzyme was developed, and it was found to be inducibly synthesized only during growth on threonine and not during growth on acetate plus glycine. 6. By using a reconstituted mixture of separately purified l-threonine dehydrogenase and alpha-amino-beta-oxobutyrate CoA-ligase (i.e. ;aminoacetone synthase'), l-[U-(14)C]threonine was broken down to [(14)C]glycine plus [(14)C]acetyl-CoA (trapped as [(14)C]citrate). 7. There was no evidence of aminoacetone metabolism by Arthrobacter 9759 even though a small amount of this amino ketone appeared in the culture medium during growth on threonine.     

Use of 3-aminopropanol as an ethanolamine analogue in the study of phospholipid metabolism in Tetrahymena.

About 50% of the ethanolamine in phosphatidylethanolamine in Tetrahymena is replaced by 3-aminopropan-1-ol when the compound is added to the growth medium. The phosphatidylpropanolamine which is formed is not converted into the corresponding phosphatidylcholine analogue by methylation. There is an increase in phosphatidylcholine formed by the phosphotransferase pathway from free [3H]choline and a decrease in the phosphatidylcholine formed by the methylation pathway from [14C]methionine. The nature of the observed phospholipid alterations suggests that the regulation of phosphatidylcholine biosynthesis in Tetrahymena may be different from that found in higher eukaryotes.     

Microbial metabolism of amino alcohols. Biosynthetic utilization of ethanolamine for lipid synthesis by bacteria.

1. Ten bacteria utilizing [2-14C]ethanol-2-amine as the sole or major source of nitrogen for growth on glycerol + salts medium incorporated radioactivity into a variety of bacterial substances. A high proportion was commonly found in lipid fractions, particularly in the case of Erwinia carotovora. 2. Detailed studies of [14C]ethanolamine incorporation into lipids by five bacteria, including E. carotovora, showed that all detectable lipids were labelled. Even where phosphatidylethanolamine was the major lipid labelled, radioactivity was predominantly in the fatty acid rather than the base moiety. The labelled fatty acids were identified in each case. 3. The addition of acetate to growth media decreased the incorporation of radioactivity from ethanolamine into both fatty acid and phosphatidyl-base fragments of lipids from all the bacteria except Mycobacterium smegmatis. Experiments with [3H]ethanolamine and [14C]acetate confirmed that unlabelled acetate decreased the incorporation of both radioactive isotopes into lipids, except in the case of M. smegmatis. 4. Enzyme studies suggested one of two metabolic routes between ethanolamine and acetyl-CoA for each of four bacteria. A role for ethanolamine O-phosphate was not obligatory for the incorporation of [14C]ethanolamine into phospholipids, but correlated with CoA-independent aldehyde dehydrogenase activity.     

DNA polymerase I function is required for the utilization of ethanolamine, 1,2-propanediol, and propionate by Salmonella typhimurium LT2.

Evidence documenting the requirement for a functional DNA polymerase I when Salmonella typhimurium LT2 uses ethanolamine (EA), 1,2-propanediol (1,2-PDL), or propionate (PRP) as the sole carbon and energy source is presented. Providing rat polymerase beta in trans demonstrated that the growth phenotypes observed were due exclusively to the lack of DNA polymerase I functions. The location of the mutation (a MudI1734 insertion) that rendered cells unable to grow on EA, 1,2-PDL, or PRP was determined by DNA sequencing to be within the polA gene. polA mutants of this bacterium may be unable to repair the damage caused by reactive aldehydes generated during the catabolism of EA, 1,2-PDL, or PRP. Consistent with this hypothesis, the inhibitory effects of acetaldehyde and propionaldehyde on the growth of this polA mutant were demonstrated. A derivative of the polA mutant unable to synthesize glutathione (GSH) was markedly more sensitive to acetaldehyde and propionaldehyde than was the polA mutant proficient in GSH synthesis. This finding was in agreement with the recently proposed role of GSH as a mechanism for quenching reactive aldehydes generated during the catabolism of these compounds (M. R. Rondon, R. Kazmierczack, and J. C. Escalante-Semerena, J. Bacteriol. 177:5434-5439, 1995).     

Production of Acetic Acid and Other Volatile Compounds by Leuconostoc citrovorum and Leuconostoc dextranicum

Single-strain milk cultures of Leuconostoc dextranicum are capable of reducing added acetaldehyde, propionaldehyde, and butanone to the corresponding alcohols at 30 C. L. dextranicum and L. citrovorum reduced propionaldehyde to n-propanol quantitatively in 30 hr, and the reduction of this compound paralleled culture growth. Under unagitated conditions, these organisms produced large amounts of acetic acid and ethyl alcohol. The yield of acetic acid increased when cultures were agitated during growth. This increase in acetic acid production was accompanied by a 20- to 70-fold decrease in ethyl alcohol. The addition of acetaldehyde to the fermentation caused a reduction in the final concentration of acetic acid.     

The formation of unhydrated propionaldehyde by dioldehydrase.

When dl-1,2-propanediol is converted to propionaldehyde by dioldehydrase, an enzyme which requires B₁₂-coenzyme, the product is unhydrated propionaldehyde. Its formation was demonstrated by measuring the rate of reduction of the enzymically formed aldehyde by NADH, catalyzed by yeast alcohol dehydrogenase.     

Amides from Streptomyces hygroscopicus and their antimicrobial activity [corrected

Three amides, N-salicyloyl-2-aminopropan-1,3-diol (1) and 1-acetyl-N-salicyloyl-2-aminopropan-3-ol (2) including a natural product, N-salicyloyl-2-aminopropan-1-ol (3) were isolated from an ethyl acetate extract of the culture filtrate of Streptomyces hygroscopicus [corrected] The structures of these compounds were unambiguously established by interpretation of their spectral data including, a series of 1D and 2D-NMR and MS analyses. Compounds 1-3 showed significant antibacterial activity against a wide range of Gram positive and Gram negative bacteria.     

Pathway of propionate formation in Desulfobulbus propionicus

Whole cells of Desulfobulbus propionicus fermented [1-¹³C]ethanol to [2-¹³C] and [3-¹³C]propionate and [1-¹³C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA: pyruvate transacetylase, acetase kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activity of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence of pyruvate, CoA and ATP and the oxaloacetate-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor.The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.Abbreviations DCPIP 2,6-dichlorophenolindophenol - PEP phosphoenolpyruvate     

Minimal functions and physiological conditions required for growth of salmonella enterica on ethanolamine in the absence of the metabolosome

During growth on ethanolamine, Salmonella enterica synthesizes a multimolecular structure that mimics the carboxysome used by some photosynthetic bacteria to fix CO(2). In S. enterica, this carboxysome-like structure (hereafter referred to as the ethanolamine metabolosome) is thought to contain the enzymatic machinery needed to metabolize ethanolamine into acetyl coenzyme A (acetyl-CoA). Analysis of the growth behavior of mutant strains of S. enterica lacking specific functions encoded by the 17-gene ethanolamine utilization (eut) operon established the minimal biochemical functions needed by this bacterium to use ethanolamine as a source of carbon and energy. The data obtained support the conclusion that the ethanolamine ammnonia-lyase (EAL) enzyme (encoded by the eutBC genes) and coenzyme B(12) are necessary and sufficient to grow on ethanolamine. We propose that the EutD phosphotransacetylase and EutG alcohol dehydrogenase are important to maintain metabolic balance. Glutathione (GSH) had a strong positive effect that compensated for the lack of the EAL reactivase EutA protein under aerobic growth on ethanolamine. Neither GSH nor EutA was needed during growth on ethanolamine under reduced-oxygen conditions. GSH also stimulated growth of a strain lacking the acetaldehyde dehydrogenase (EutE) enzyme. The role of GSH in ethanolamine catabolism is complex and requires further investigation. Our data show that the ethanolamine metabolosome is not involved in the biochemistry of ethanolamine catabolism. We propose the metabolosome is needed to concentrate low levels of ethanolamine catabolic enzymes, to keep the level of toxic acetaldehyde low, to generate enough acetyl-CoA to support cell growth, and to maintain a pool of free CoA.     

Ethanolamine utilization in Salmonella typhimurium: nucleotide sequence, protein expression, and mutational analysis of the cchA cchB eutE eutJ eutG eutH gene cluster.

A fragment of the Salmonella typhimurium ethanolamine utilization operon was cloned and characterized. The 6.3-kb nucleotide sequence encoded six complete open reading frames, termed cchA, cchB, eutE, eutJ, eutG, and eutH. In addition, the nucleotide sequences of two incomplete open reading frames, termed eutX and eutI, were also determined. Comparison of the deduced amino acid sequences and entries in the GenBank database indicated that eutI encodes a phosphate acetyltransferase-like enzyme. The deduced amino acid sequences of the EutE and EutG proteins revealed a significant degree of homology with the Escherichia coli alcohol dehydrogenase AdhE sequence. Mutations in eutE or eutG completely abolished the ability of mutants to utilize ethanolamine as a carbon source and reduced the ability to utilize ethanolamine as a nitrogen source. The product of eutE is most probably an acetaldehyde dehydrogenase catalyzing the conversion of acetaldehyde into acetyl coenzyme A. The product of the eutG gene, an uncommon iron-containing alcohol dehydrogenase, may protect the cell from unconverted acetaldehyde by converting it into an alcohol. The deduced amino acid sequence of cchA resembles that of carboxysome shell proteins from Thiobacillus neapolitanus and Synechococcus sp. as well as that of the PduA product from S. typhimurium. CchA and CchB proteins may be involved in the formation of an intracellular microcompartment responsible for the metabolism of ethanolamine. The hydrophobic protein encoded by the eutH gene possesses some characteristics of bacterial permeases and might therefore be involved in the transport of ethanolamine. Ethanolamine-utilization mutants were slightly attenuated in a mouse model of S. typhimurium infection, indicating that ethanolamine may be an important source of nitrogen and carbon for S. typhimurium in vivo.     

Pyruvate decarboxylase: a key enzyme for the oxidative metabolism of lactic acid by Acetobacter pasteurianus

Acetobacter pasteurianus, an obligately oxidative bacterium, is the first organism shown to utilize pyruvate decarboxylase (PDC) as a central enzyme for oxidative metabolism. In plants, yeast, and other bacteria, PDC functions solely as part of the fermentative ethanol pathway. During the growth of A. pasteurianus on lactic acid, the central intermediate pyruvate is cleaved to acetaldehyde and CO(2) by PDC. Acetaldehyde is subsequently oxidized to its final product, acetic acid. The presence of the PDC enzyme in A. pasteurianus was confirmed by zymograms stained for acetaldehyde production, enzyme assays using alcohol dehydrogenase as the coupling enzyme, and by cloning and characterization of the pdc operon. A. pasteurianus pdc was also expressed in recombinant Escherichia coli. The level of PDC activity was regulated in response to growth substrate, highest with lactic acid and absent with mannitol. The translated PDC sequence (548 amino acids) was most similar to that of Zymomonas mobilis, an obligately fermentative bacterium. A second operon ( aldA) was also found which is transcribed divergently from pdc. This operon encodes a putative aldehyde dehydrogenase (ALD2; 357 amino acids) related to class III alcohol dehydrogenases and most similar to glutathione-dependent formaldehyde dehydrogenases from alpha-Proteobacteria and Anabeana azollae.     

Propionate formation from alcohols or aldehydes by Desulfobulbus propionicus in the absence of sulfate

Fermentative degradation of alcohols and aldehydes in the absence of sulfate was investigated using a propionate-oxidizing, sulfate-reducing bacterium, Desulfobulbus propionicus strain MUD (DSM 6523). The organism converted ethanol plus CO₂ to acetate and propionate. The conversion was not affected by the presence of hydrogen. Strain MUD converted propanol plus acetate to propionate. Acetaldehyde and propionaldehyde were also converted with a dismutation reaction in the absence of sulfate. The products were propionate and acetate from acetaldehyde, and propionate from propionaldehyde plus acetate.