Purification and characterization of monoamine oxidase from Klebsiella aerogenes

Reduction of histamine and biogenic amines during salted fish fermentation by Bacillus polymyxa as a starter culture

Bacillus polymyxa D05-1, isolated from salted fish product and possessing amine degrading activity, was used as a starter culture in salted fish fermentation in this study. Fermentation was held at 35°C for 120 days. The water activity in control samples (without starter culture) and inoculated samples (inoculated with B. polymyxa D05-1) remained constant throughout fermentation, whereas the pH value rose slightly during fermentation. Salt contents in both samples were constant in the range of 17.5–17.8% during the first 60 days of fermentation and thereafter increased slowly. The inoculated samples had considerably lower levels of total volatile basic nitrogen (p < 0.05) than control samples at each sampling time during 120 days of fermentation. Aerobic bacterial counts in inoculated samples were retarded during the first 60 days of fermentation and thereafter increased slowly, whereas those of control samples increased rapidly with increased fermentation time. However, the aerobic bacterial counts of control samples were significantly higher (p < 0.05) than those of inoculated samples after 40 days of fermentation. In general, overall biogenic amine contents (including histamine, putrescine, cadaverine, and tyramine) in the control samples were markedly higher (p < 0.05) than those of the inoculated samples throughout fermentation. After 120 days of fermentation, the histamine and overall biogenic amine contents in the inoculated samples were reduced by 34.0% and 30.0%, respectively, compared to control samples. These results emphasize that the application of starter culture with amines degrading activity in salted fish products was effective in reducing biogenic amine accumulation.

Degradation of histamine by Bacillus polymyxa isolated from salted fish products

Histamine is the causative agent of scombroid poisoning, a foodborne chemical hazard. Histamine is degraded by the oxidative deamination activity of certain microorganisms. In this study, eight histamine-degrading bacteria isolated from salted fish products were identified as Rummeliibacillus stabekisii (1 isolate), Agrobacterium tumefaciens (1 isolate), Bacillus cereus (2 isolates), Bacillus polymyxa (1 isolate), Bacillus licheniformis (1 isolate), Bacillus amyloliquefaciens (1 isolate), and Bacillus subtilis (1 isolate). Among them, B. polymyxa exhibited the highest activity in degrading histamine than the other isolates. The ranges of temperature, pH, and salt concentration for growth and histamine degradation of B. polymyxa were 25–37°C, pH 5–9, and 0.5–5% NaCl, respectively. B. polymyxa exhibited optimal growth and histamine-degrading activity at 30°C, pH 7, and 0.5% NaCl in histamine broth for 24 hours of incubation. The histamine-degrading isolate, B. polymyxa, might be used as a starter culture in inhibiting histamine accumulation during salted fish product fermentation.

Potential of wine-associated lactic acid bacteria to degrade biogenic amines

Some lactic acid bacteria (LAB) isolated from fermented foods have been proven to degrade biogenic amines through the production of amine oxidase enzymes. Since little is known about this in relation to wine micro-organisms, this work examined the ability of LAB strains (n=85) isolated from wines and other related enological sources, as well as commercial malolactic starter cultures (n=3) and type strains (n=2), to degrade histamine, tyramine and putrescine. The biogenic amine-degrading ability of the strains was evaluated by RP-HPLC in culture media and wine malolactic fermentation laboratory experiments. Although at different extent, 25% of the LAB isolates were able to degrade histamine, 18% tyramine and 18% putrescine, whereas none of the commercial malolactic starter cultures or type strains were able to degrade any of the tested amines. The greatest biogenic amine-degrading ability was exhibited by 9 strains belonging to the Lactobacillus and Pediococcus groups, and most of them were able to simultaneously degrade at least two of the three studied biogenic amines. Further experiments with one of the strains that showed high biogenic amine-degrading ability (L. casei IFI-CA 52) revealed that cell-free extracts maintained this ability in comparison to the cell suspensions at pH 4.6, indicating that amine-degrading enzymes were effectively extracted from the cells and their action was optimal in the degradation of biogenic amines. In addition, it was confirmed that wine components such as ethanol (12%) and polyphenols (75 mg/L), and wine additives such as SO(2) (30 mg/L), reduced the histamine-degrading ability of L. casei IFI-CA 52 at pH 4.6 by 80%, 85% and 11%, respectively, in cell suspensions, whereas the reduction was 91%, 67% and 50%, respectively, in cell-free extracts. In spite of this adverse influence of the wine matrix, our results proved the potential of wine-associated LAB as a promising strategy to reduce biogenic amines in wine.

Syntrophic degradation of cadaverine by a defined methanogenic coculture

A novel, strictly anaerobic, cadaverine-oxidizing, defined coculture was isolated from an anoxic freshwater sediment sample. The coculture oxidized cadaverine (1,5-diaminopentane) with sulfate as the electron acceptor. The sulfate-reducing partner could be replaced by a hydrogenotrophic methanogenic partner. The defined coculture fermented cadaverine to acetate, butyrate, and glutarate plus sulfide or methane. The key enzymes involved in cadaverine degradation were identified in cell extracts. A pathway of cadaverine fermentation via 5-aminovaleraldehyde and crotonyl-coenzyme A with subsequent dismutation to acetate and butyrate is suggested. Comparative 16S rRNA gene analysis indicated that the fermenting part of the coculture belongs to the subphylum Firmicutes but that this part is distant from any described genus. The closest known relative was Clostridium aminobutyricum, with 95% similarity.

Histamine and tyramine degradation by food fermenting microorganisms

Microorganisms suitable for food fermentation were examined with regard to their potential to degrade histamine and tyramine. Out of 64 lactic acid bacteria evaluated in this study, 27 degraded histamine and one tyramine, respectively, with low activity. Among 32 strains of Brevibacterium linens and coryneform bacteria, 21 exhibited histamine and tyramine oxidase activity. None of 20 strains of Staphylococcus carnosus tested degraded histamine or tyramine. One strain out of nine strains of Geotrichum candidum degraded tyramine slightly. Among 44 strains of Micrococcus sp. examined, 17 degraded either one or two biogenic amines. In this study Micrococcus varians (M. varians) LTH 1540 exhibited the highest tyramine oxidase activity of all strains tested and was therefore investigated in detail. The enzyme was found to be located in the cytoplasm and was not membrane bound. The reaction end product p-hydroxyphenyl acetic acid was detected by HPLC analysis. An activity staining for the amine oxidase in a native polyacrylamide gel based on the formation of H2O2 during amine oxidation was developed. Resting cells of the strain exhibited optimal tyramine oxidase activity at a pH of 7 at 37-40 degrees C. The enzyme in the cell free extract had a pH optimum between 7-8. The enzyme activity was decreased by NaCl, glucose and hydralazine. Phenylethylamine and tryptamine were oxidized at lower concentrations than tyramine. The potential for amine degradation was not found to be associated with that of formation of biogenic amines, as 23 microorganisms with the ability to metabolise biogenic amines exhibited no decarboxylase activity toward histidine, tyrosine, phenylalanine, lysine or ornithine.

2-phenylethylamine catabolism by Escherichia coli K-12: gene organization and expression

A gene encoding phenylacetaldehyde dehydrogenase (PAD), the enzyme involved together with a copper-topaquinone-containing amine oxidase in the initial steps of 2-phenylethylamine catabolism, was located at 31.1 min on the Escherichia coli K-12 genetic map. It was immediately adjacent to the gene encoding the amine oxidase but transcribed in the opposite direction. The purified PAD acted almost equally well on phenylacetaldehyde, 4-hydroxyphenylacetaldehyde and 3,4-dihydroxyphenylacetaldehyde. It had a subunit size of 54 kDa and its deduced amino acid sequence was approximately 40% identical to various eukaryotic and prokaryotic aldehyde dehydrogenases. A third gene encoding a positive regulatory protein required for expression of the amine oxidase and PAD genes was located next to the PAD gene. A gene previously located in this position was reported to encode a second amine oxidase but this was not confirmed. The nucleotide sequence from 1447 to 1450 kb on the E. coli K-12 physical map has been determined.

Distribution of amine oxidases and amine dehydrogenases in bacteria grown on primary amines and characterization of the amine oxidase from Klebsiella oxytoca

The bacteria Klebsiella oxytoca LMD 72.65 (ATCC 8724), Arthrobacter P1 LMD 81.60 (NCIB 11625), Paracoccus versutus LMD 80.62 (ATCC 25364), Escherichia coli W LMD 50.28 (ATCC 9637), E. coli K12 LMD 93.68, Pseudomonas aeruginosa PAO1 LMD 89.1 (ATCC 17933) and Pseudomonas putida LMD 68.20 (ATCC 12633) utilized primary amines as a carbon and energy source, although the range of amines accepted varied from organism to organism. The Gram-negative bacteria K. oxytoca and E. coli as well as the Gram-positive methylotroph Arthrobacter P1 used an oxidase whereas the pseudomonads and the Gram-negative methylotroph Paracoccus versutus used a dehydrogenase for amine oxidation. K. oxytoca utilized several primary amines but showed a preference for those containing a phenyl group moiety. Only a single oxidase was used for oxidation of the amines. After purification, the following characteristics of the enzyme indicated that it belonged to the group of copper-quinoprotein amine oxidase (EC 1.4.3.6): the molecular mass (172,000 Da) of the homodimeric protein; the UV/visible and EPR spectra of isolated and p-nitrophenylhydrazine-inhibited enzyme; the presence and the content of copper and topaquinone (TPQ). The amine oxidase appeared to be soluble and localized in the periplasm, but catalase and NAD-dependent aromatic aldehyde dehydrogenase, enzymes catalysing the conversion of its reaction products, were found in the cytoplasm. From the amino acid sequence of the N-terminal part as well as that of a purified peptide, it appears that K. oxytoca produces a copper-quinoprotein oxidase which is very similar to that found in other Enterobacteriaceae.

On the amine oxidases of Klebsiella aerogenes strain W70

Klebsiella aerogenes W70 was reported previously to produce a membrane-associated tyramine oxidase (TynA) that did not act on 2-phenylethylamine. Subsequently, a gene cloned from K. aerogenes W70 produced a soluble amine oxidase (MaoA) that acted readily on 2-phenylethylamine and tyramine. This enzyme appeared to be equivalent to a 2-phenylethylamine oxidase of Escherichia coli K-12 (MaoA) but was assumed to be the originally described K. aerogenes W70 tyramine oxidase (TynA). However, as described here, whole cells and cell-free extracts of K. aerogenes W70 showed only the tyramine oxidase (TynA) that is inactive against 2-phenylethylamine and not the maoA gene product. It seems that the organism has two amine oxidase genes, tynA and maoA, but only tynA is expressed. Hence, data relating to the expression of the K. aerogenes W70 tynA gene cannot be assumed to apply to the maoA gene of E. coli K-12 because they encode different enzymes.

Two amine oxidases from Aspergillus niger AKU 3302 contain topa quinone as the cofactor: unusual cofactor link to the glutamyl residue occurs only at one of the enzymes

Amine oxidases (EC 1.4.3.6) from Aspergillus niger, AO-I (2 x 75 kDa) and AO-II (80 kDa), were examined to determine the cofactor structure. Inactivated with p-nitrophenylhydrazine, they showed absorption and fluorescence spectra similar to those published for other copper amine oxidases and to topa hydantoin p-nitrophenylhydrazone. After digestion by thermolysin and pronase, cofactor peptides were purified by HPLC and sequenced. For thermolytic peptides, a typical topa consensus sequence, Asn-X-Glu-Tyr, was obtained for AO-II, although in case of AO-I it overlapped with Val-Val-Ile-Glu-Pro-Tyr-Gly. For pronase peptides of AO-I, only the latter sequence was obtained. NMR and mass spectroscopy confirmed the residue X as topa p-nitrophenylhydrazone in AO-II and revealed the presence of a residue Z attached to the Glu in the peptide Val-Val-Ile-Glu(Z)-Pro of AO-I. This residue was separated from the peptide by hydrolysis and identified as a product derived from topa quinone. The data, together with amino-acid sequence of AO-I, confer strong evidence for topa quinone as the cofactor, bound in the typical consensus sequence. Raman spectra of the p-nitrophenylhydrazone derivative of AO-I and its pronase peptide showed essentially the same peaks matching to a model compound for topa p-nitrophenylhydrazone. However, there may exist an unusual ester link between the topa-404 and Glu-145 in the native enzyme.

maoB, a gene that encodes a positive regulator of the monoamine oxidase gene (maoA) in Escherichia coli

The structural gene for copper- and topa quinone-containing monoamine oxidase (maoA) and an unknown amine oxidase gene have been located at 30.9 min on the Escherichia coli chromosome. Deletion analysis showed that the unknown gene was located within a 1.1-kb cloned fragment adjacent to the maoA gene. The nucleotide sequence of this fragment was determined, and a single open reading frame (maoB) consisting of 903 bp was found. The gene encoded a polypeptide with a predicted molecular mass of 34,619 Da which was correlated with the migration on a sodium dodecyl sulfate-polyacrylamide gel. The predicted amino acid sequence of the MaoB protein was identical to the NH2-terminal amino acid sequence derived by Edman degradation of the protein synthesized under the self-promoter. No homology of the nucleotide sequence of maoB to the sequences of any reported genes was found. However, the amino acid sequence of MaoB showed a high level of homology with respect to the helix-turn-helix motif of the AraC family in its C terminus. The homology search and disruption of maoA on the chromosome led to the conclusion that MaoB is a transcriptional activator of maoA but not an amine oxidase. The consensus sequence of the cyclic AMP-cyclic AMP receptor protein complex binding domain was adjacent to the putative promoter for the maoB gene. By use of lac gene fusions with the maoA and maoB genes, we showed that the maoA gene is regulated by tyramine and MaoB and that the expression of the maoB gene is subject to catabolite repression. Thus, it seems likely that tyramine and the MaoB protein activate the transcription of maoA by binding to the regulatory region of the maoA gene.

Two distinct quinoprotein amine oxidases are induced by n-butylamine in the mycelia of Aspergillus niger AKU 3302. Purification, characterization, cDNA cloning and sequencing

Two distinct quinoprotein amine oxidases were found in Aspergillus niger mycelia grown on n-butylamine medium and purified using chromatographic techniques. The respective enzymes were termed AO-I, which had already been isolated, and AO-II, a new enzyme found in this study. HPLC indicated that their molecular masses are 150 kDa and 80 kDa, respectively. On SDS/PAGE, the enzymes gave a similar but distinct mobility, which corresponds to 75 kDa for the subunit dimeric AO-I and 80 kDa for monomeric AO-II. The absorption spectra of both enzymes were different from each other; the absorption maxima in the visible region were at 490 nm for AO-I and 420 nm for AO-II. The enzymes showed positive quinone staining, comparable substrate specificity, and sensitivity to inhibitors typical for copper/topa quinone-containing amine oxidases, but they had different copper contents and also differed in their N-terminal sequences. Their peptide maps showed almost identical patterns, with the exception of two additional bands for AO-II. Among the peptides obtained from digestion of AO-II, peptides with sequences corresponding to the N-terminal part of AO-I were detected. Polyclonal antibodies raised against AO-I and AO-II recognized both enzymes, but with different specificities. Using precipitation with AO-I, the antibody prepared against AO-II was purified and was shown to be specific only for AO-II. The cDNA of AO-I was cloned and sequenced. A highly conserved tetrapeptide sequence, Asn-Tyr-Glu-Tyr, was identified in which the first tyrosine residue (Tyr404) that could be converted to topa quinone was present in the 670-residue deduced amino acid sequence. Northern blot analysis indicated that AO-I was highly expressed in A. niger grown on n-butylamine as a single nitrogen source. Genomic Southern blot analysis confirmed that both enzymes are likely to be encoded by the same gene.

Active-site covalent modifications of quinoprotein amine oxidases from Aspergillus niger. Evidence for binding of the mechanism-based inhibitor, 1,4-diamino-2-butyne, to residue Lys356 involved in the catalytic cycle

Interactions of two distinct quinoprotein amine oxidases from Aspergillus niger, AO-I and AO-II, with active-site covalent modifiers have been investigated. Both enzymes are inhibited similarly by phenylhydrazine or p-nitrophenylhydrazine, forming an orange Schiff base with a carbonyl group of topaquinone cofactor. Modification of histidyl and tyrosyl residues by diethylpyrocarbonate and sulfhydryl groups by 5,5'-dithio-bis-(2-nitrobenzoic acid) and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole have been described. A substrate analog, 1,4-diamino-2-butyne, was found to function as a mechanism-based inhibitor. It shows both substrate saturation kinetics and time-dependent irreversible inhibition caused by formation of pyrrole bound to the active site. The pyrrole formation was confirmed spectrophotometrically by reaction with Ehrlich's reagent at 525 nm. Inhibition by 1,4-diamino-2-butyne produces a new maximum in the absorption spectra of AO-I and AO-II at 310 nm and 306 nm, respectively. Inactivated AO-I was digested by proteases; labeled peptides were purified by C18 HPLC and sequenced by Edman degradation. Data reveal the evidence that 1,4-diamino-2-butyne reacts with the epsilon-amino group of the Lys356 residue in the sequence Lys-Met-Pro-Asn-Ala of Aspergillus niger amine oxidase AO-I.