The ant Lasius niger is a new source of bacterial enzymes with biotechnological potential for bleaching dye

Industrial synthetic dyes cause health and environmental problems. This work describes the isolation of 84 bacterial strains from the midgut of the Lasius niger ant and the evaluation of their potential application in dye bioremediation. Strains were identified and classified as judged by rRNA 16S. The most abundant isolates were found to belong to Actinobacteria (49%) and Firmicutes (47.2%). We analyzed the content in laccase, azoreductase and peroxidase activities and their ability to degrade three known dyes (azo, thiazine and anthraquinone) with different chemical structures. Strain Ln26 (identified as Brevibacterium permense) strongly decolorized the three dyes tested at different conditions. Strain Ln78 (Streptomyces ambofaciens) exhibited a high level of activity in the presence of Toluidine Blue (TB). It was determined that 8.5 was the optimal pH for these two strains, the optimal temperature conditions ranged between 22 and 37 °C, and acidic pHs and temperatures around 50 °C caused enzyme inactivation. Finally, the genome of the most promising candidate (Ln26, approximately 4.2 Mb in size) was sequenced. Genes coding for two DyP-type peroxidases, one laccase and one azoreductase were identified and account for the ability of this strain to effectively oxidize a variety of dyes with different chemical structures.

Effects of transgenic expression of Brevibacterium linens methionine gamma lyase (MGL) on accumulation of Tylenchulus semipenetrans and key aminoacid contents in Carrizo citrange

Carrizo transgenic plants overexpressing methionine-gamma-lyase produced dimethyl sulfide. The transgenic plants displayed more resistance to nematode attacks (Tylenculus semipenetrans) and may represent an innovative strategy for nematode control. Tylenchulus semipenetrans is a nematode pest of many citrus varieties that causes extensive damage to commercial crops worldwide. Carrizo citrange vr. (Citrus sinensis L. Usb × Poncirus trifoliate L. Raf) plants overexpressing Brevibacterium linens methionine-gamma-lyase (BlMGL) produced the sulfur volatile compound dimethyl sulfide (DMS). The aim of this work was to determine if transgenic citrus plants expressing BlMGL showed increased tolerance to T. semipenetrans infestation and to determine the effect on the content of key amino acids. While transgenic lines emitted dimethyl sulfide from leaves and roots, no sulfur-containing volatiles were detectable in wild-type Carrizo in the same tissues. Significant changes detected some key amino acids from leaves of transgenic plants such as aspartate, lysine, glycine, leucine and threonine with no changes in the amounts of methionine and α-ketobutyrate. In roots only glycine showed significant changes across all transgenic lines in comparison to wild-type plants. Transgenic plants expressing BlMGL and emitting DMS had less T. semipenetrans aggregation and more biomass than infected WT control plants, indicating that they may represent an innovative management alternative to pesticide/nematicide-based remedies.

Hyperexpression and Analysis ofchoBEncoding Cholesterol Oxidase ofBrevibacterium sterolicuminEscherichia coliandStreptomyces lividans

We examined the expression of choB, encoding cholesterol oxidase of Brevibacterium sterolicum ATCC 21387, in Escherichia coli JM105 and Streptomyces lividans TK23 using various deletion DNA fragments within the 5'-flanking region. The enzyme activity could be detected intracellularly in E. coli only when the 5'-flanking region was reduced to less than 256-bp and choB was transcribed by the lac promoter. A large amount of the enzyme were produced as inactive inclusion bodies when ChoB protein was fused with the NH2-terminal portion of LacZ protein. In contrast, choB with more than 256-bp of the 5'-flanking region was efficiently expressed in S. lividans TK23, and about 85 times as much of the active enzyme (170 U/ml) was secreted into the culture filtrate as with B. sterolicum in flask culture. These results suggest that the promoter of choB exist within 256-bp of the 5'-flanking region and can be efficiently recognized by the RNA polymerase of S. lividans. The characteristics of the enzyme purified from the culture filtrate of the S. lividans transformant and that of B. sterolicum were identical although the NH2-terminal amino acid sequence of the enzyme from the S. lividans transformant was 6 amino acids shorter than that from B. sterolicum.

Structural analysis of a novel cyclohexylamine oxidase from Brevibacterium oxydans IH-35A

Cyclohexylamine oxidase (CHAO) is a flavoprotein first described in Brevibacterium oxydans strain IH-35A that carries out the initial step of the degradation of the industrial chemical cyclohexylamine to cyclohexanone. We have cloned and expressed in Escherichia coli the CHAO-encoding gene (chaA) from B. oxydans, purified CHAO and determined the structures of both the holoenzyme form of the enzyme and a product complex with cyclohexanone. CHAO is a 50 kDa monomer with a PHBH fold topology. It belongs to the flavin monooxygenase family of enzymes and exhibits high substrate specificity for alicyclic amines and sec-alkylamines. The overall structure is similar to that of other members of the flavin monooxygenase family, but lacks either of the C- or N-terminal extensions observed in these enzymes. Active site features of the flavin monooxygenase family are conserved in CHAO, including the characteristic aromatic cage. Differences in the orientations of residues of the CHAO aromatic cage result in a substrate-binding site that is more open than those of its structural relatives. Since CHAO has a buried hydrophobic active site with no obvious route for substrates and products, a random acceleration molecular dynamics simulation has been used to identify a potential egress route. The path identified includes an intermediate cavity and requires transient conformation changes in a shielding loop and a residue at the border of the substrate-binding cavity. These results provide a foundation for further studies with CHAO aimed at identifying features determining substrate specificity and for developing the biocatalytic potential of this enzyme.

Phospholipid-sepiolite biomimetic interfaces for the immobilization of enzymes

Biomimetic interfaces based on phosphatidylcholine (PC) assembled to the natural silicate sepiolite were prepared for the stable immobilization of the urease and cholesterol oxidase enzymes. This is an important issue in practical advanced applications such as biocatalysis or biosensing. The supported lipid bilayer (BL-PC), prepared from PC adsorption, was used for immobilization of enzymes and the resulting biomimetic systems were compared to several other supported layers including a lipid monolayer (ML-PC), a mixed phosphatidylcholine/octyl-galactoside layer (PC-OGal), a cetyltrimethylammonium monolayer (CTA), and also to the bare sepiolite surface. Interfacial characteristics of these layers were investigated with a focus on layer packing density, hydrophilicity/hydrophobicity, and surface charge, which are being considered as key points for enzyme immobilization and stabilization of their biological activity. Cytoplasmic urease and membrane-bound cholesterol oxidase, which served as model enzymes, were immobilized on the different PC-based hybrid materials to probe their biomimetic character. Enzymatic activity was assessed by cyclic voltammetry and UV-vis spectrophotometry. The resulting enzyme/bio-organoclay hybrids were applied as active phase of a voltammetric urea biosensor and cholesterol bioreactor, respectively. Urease supported on sepiolite/BL-PC proved to maintain its enzymatic activity over several months while immobilized cholesterol oxidase demonstrated high reusability as biocatalyst. The results emphasize the good preservation of bioactivity due to the accommodation of the enzymatic system within the biomimetic lipid interface on sepiolite.

A hyperactive cobalt-substituted extradiol-cleaving catechol dioxygenase

Homoprotocatechuate 2,3-dioxygenase from Brevibacterium fuscum (HPCD) has an Fe(II) center in its active site that can be replaced with Mn(II) or Co(II). Whereas Mn-HPCD exhibits steady-state kinetic parameters comparable to those of Fe-HPCD, Co-HPCD behaves somewhat differently, exhibiting significantly higher [Formula: see text] and k (cat). The high activity of Co-HPCD is surprising, given that cobalt has the highest standard M(III/II) redox potential of the three metals. Comparison of the X-ray crystal structures of the resting and substrate-bound forms of Fe-HPCD, Mn-HPCD, and Co-HPCD shows that metal substitution has no effect on the local ligand environment, the conformational integrity of the active site, or the overall protein structure, suggesting that the protein structure does not differentially tune the potential of the metal center. Analysis of the steady-state kinetics of Co-HPCD suggests that the Co(II) center alters the relative rate constants for the interconversion of intermediates in the catalytic cycle but still allows the dioxygenase reaction to proceed efficiently. When compared with the kinetic data for Fe-HPCD and Mn-HPCD, these results show that dioxygenase catalysis can proceed at high rates over a wide range of metal redox potentials. This is consistent with the proposed mechanism in which the metal mediates electron transfer between the catechol substrate and O(2) to form the postulated [M(II)(semiquinone)superoxo] reactive species. These kinetic differences and the spectroscopic properties of Co-HPCD provide new tools with which to explore the unique O(2) activation mechanism associated with the extradiol dioxygenase family.

Global regulation of the response to sulfur availability in the cheese-related bacterium Brevibacterium aurantiacum

In this study, we combined metabolic reconstruction, growth assays, and metabolome and transcriptome analyses to obtain a global view of the sulfur metabolic network and of the response to sulfur availability in Brevibacterium aurantiacum. In agreement with the growth of B. aurantiacum in the presence of sulfate and cystine, the metabolic reconstruction showed the presence of a sulfate assimilation pathway, thiolation pathways that produce cysteine (cysE and cysK) or homocysteine (metX and metY) from sulfide, at least one gene of the transsulfuration pathway (aecD), and genes encoding three MetE-type methionine synthases. We also compared the expression profiles of B. aurantiacum ATCC 9175 during sulfur starvation or in the presence of sulfate. Under sulfur starvation, 690 genes, including 21 genes involved in sulfur metabolism and 29 genes encoding amino acids and peptide transporters, were differentially expressed. We also investigated changes in pools of sulfur-containing metabolites and in expression profiles after growth in the presence of sulfate, cystine, or methionine plus cystine. The expression of genes involved in sulfate assimilation and cysteine synthesis was repressed in the presence of cystine, whereas the expression of metX, metY, metE1, metE2, and BL613, encoding a probable cystathionine-γ-synthase, decreased in the presence of methionine. We identified three ABC transporters: two operons encoding transporters were transcribed more strongly during cysteine limitation, and one was transcribed more strongly during methionine depletion. Finally, the expression of genes encoding a methionine γ-lyase (BL929) and a methionine transporter (metPS) was induced in the presence of methionine in conjunction with a significant increase in volatile sulfur compound production.

Purification and characterization of aldehyde dehydrogenase with a broad substrate specificity originated from 2-phenylethanol-assimilating Brevibacterium sp. KU1309

Phenylacetaldehyde dehydrogenase (PADH) was purified and characterized from Brevibacterium sp. KU1309, which can grow on the medium containing 2-phenylethanol as the sole carbon source. This enzyme was a homotetrameric protein with a subunit of 61 kDa. The enzyme catalyzed the oxidation of aryl (benzaldehyde, phenylacetaldehyde, 3-phenylpropionaldehyde) and aliphatic (hexanal, octanal, decanal) aldehydes to the corresponding carboxylic acids using NAD(+) as the electron acceptor. The PADH activity was enhanced by several divalent cationic ions such as Mg(2+), Ca(2+), and Mn(2+). On the other hand, it was inhibited by SH reagents (Hg(2+), p-chloromercuribenzoate, iodoacetamide, and N-ethylmaleinimide). The substrate specificity of the enzyme is compared with those of various aldehyde dehydrogenases.

Crystal structures of Fe2+ dioxygenase superoxo, alkylperoxo, and bound product intermediates

We report the structures of three intermediates in the O2 activation and insertion reactions of an extradiol ring-cleaving dioxygenase. A crystal of Fe2+-containing homoprotocatechuate 2,3-dioxygenase was soaked in the slow substrate 4-nitrocatechol in a low O2 atmosphere. The x-ray crystal structure shows that three different intermediates reside in different subunits of a single homotetrameric enzyme molecule. One of these is the key substrate-alkylperoxo-Fe2+ intermediate, which has been predicted, but not structurally characterized, in an oxygenase. The intermediates define the major chemical steps of the dioxygenase mechanism and point to a general mechanistic strategy for the diverse 2-His-1-carboxylate enzyme family.

Development of a large scale process for the conversion of polysialogangliosides to monosialotetrahexosylganglioside with a novel strain of Brevibacterium casei producing sialidase

A bioconversion process of producing GM1 (monosialotetrahexosylganglioside) on an industrial scale was developed with a novel sialidase-producing strain Brevibacterium casei. The sialidase hydrolyzed polysialogangliosides to produce GM1 but did not act on GM1. When Brevibacterium casei was cultured in a synthetic medium containing crude pig brain gangliosides (10% w/v) at 30 degrees C for 24 h in a 50 l fermenter, most of the polysialogangliosides were converted to GM1. The content of GM1 was increased from 9% in crude gangliosides to 45% with 70% (w/w) yield.

Coenzyme precursor-assisted expression of a cholesterol oxidase from Brevibacterium sp. in Escherichia coli

The gene (choB(b)), encoding cholesterol oxidase from Brevibacterium sp. CCTCC M201008, was cloned and sequenced by PCR (GenBank accession number: DQ345780). The gene consists of 1653 base pairs and encodes a protein of 551 amino acids. ChoB(b) exhibited a homology of 98% with cholesterol oxidase gene from Brevibacterium sterolicum ATCC 21387. The cholesterol oxidase gene, cloned in the vector pET-28a, was over-expressed in Escherichia coli BL21-CodonPlus (DE3)-RP grown at 23 degrees C in Luria-Bertani medium containing 50 microM riboflavin, the precursor of the FAD coenzyme of the enzyme. A maximum activity of 3.7 U/mg was obtained from cell free extract of E. coli BL21-CodonPlus (DE3)-RP harboring the pET-28a-choB(b).

Structural and kinetic analyses of the H121A mutant of cholesterol oxidase

Cholesterol oxidase is a monomeric flavoenzyme that catalyses the oxidation of cholesterol to cholest-5-en-3-one followed by isomerization to cholest-4-en-3-one. The enzyme from Brevibacterium sterolicum contains the FAD cofactor covalently bound to His121. It was previously demonstrated that the H121A substitution results in a approximately 100 mV decrease in the midpoint redox potential and a approximately 40-fold decrease in turnover number compared to wild-type enzyme [Motteran, Pilone, Molla, Ghisla and Pollegioni (2001) Journal of Biological Chemistry 276, 18024-18030]. A detailed kinetic analysis of the H121A mutant enzyme shows that the decrease in turnover number is largely due to a corresponding decrease in the rate constant of flavin reduction, whilst the re-oxidation reaction is only marginally altered and the isomerization reaction is not affected by the substitution and precedes product dissociation. The X-ray structure of the mutant protein, determined to 1.7 A resolution (1 A identical with 0.1 nm), reveals only minor changes in the overall fold of the protein, namely: two loops have slight movements and a tryptophan residue changes conformation by a rotation of 180 degrees about chi1 compared to the native enzyme. Comparison of the isoalloxazine ring moiety of the FAD cofactor between the structures of the native and mutant proteins shows a change from a non-planar to a planar geometry (resulting in a more tetrahedral-like geometry for N5). This change is proposed to be a major factor contributing to the observed alteration in redox potential. Since a similar distortion of the flavin has not been observed in other covalent flavoproteins, it is proposed to represent a specific mode to facilitate flavin reduction in covalent cholesterol oxidase.

Application of Streptomyces and Brevibacterium cholesterol oxidase for total serum cholesterol assay by the enzymatic kinetic method

BACKGROUND

Using non-esterified cholesterol standard, Brevibacterium and Streptomyces are found as suitable sources of cholesterol oxidase for kinetic cholesterol assay. For clinical use, we investigated the suitability of these enzymes for cholesterol determination in human serum.

METHODS

We compared the performance of reagents containing 2 enzymes for the kinetic determination of total serum cholesterol with the standardized endpoint method.

RESULTS

Reagent containing Streptomyces enzyme was more sensitive than that of Brevibacterium, with linearity up to 20.7 and 2.6 mmol/l, respectively. The analytical reaction for Streptomyces showed a shorter lag phase (148 s) and a steeper slope (absorbance vs. time) than that of Brevibacterium (246 s). The assay using Streptomyces reagent was precise and accurate and compared favorably with the endpoint method (y=1.06x-0.15, r=0.996, bias=0.21 mmol/l). Hemoglobin as high as 7.5 g/l did not interfere while turbidity greater than 2+ (absorbance >0.778 at 670 nm) and bilirubin concentrations >171.0 micromol/l did interfere (in a negative interference). Reagent was stable up to at least 8 weeks.

CONCLUSIONS

The Streptomyces cholesterol oxidase, with 3,4-dichlorophenol, proved a suitable source for serum total cholesterol determination by the kinetic method.

Performance characteristics of cholesterol oxidase for kinetic determination of total cholesterol

The enzymatic method for cholesterol determination can use either an endpoint or a kinetic method. Not much is known concerning the properties (K(m) and V(max)) of the commercial enzyme for the kinetic method. We measured the K(m) and V(max) of Brevibacterium, Streptomyces, Pseudomonas fluorescens, and Cellulomonas cholesterol oxidase. Brevibacterium gave the highest K(m) value (230.3 x 10(-4) M), followed by Streptomyces (2.17 x 10(-4) M), Cellulomonas (0.84 x 10(-4) M), and Pseudomonas (0.61 x 10(-4) M). The K(m) values and the linearity obtained from Streptomyces (2.6 mmol/L), Pseudomonas (2.1 mmol/L), or Cellulomonas (2.1 mmol/L) were too low. Dichlorophenol isomers, acting as inhibitors, increased the enzyme's K(m). The addition of 3,4-dichlorophenol raised the K(m) of Streptomyces from 2.17 x 10(-4) to 24.89 x 10(-4) M. The linearity was increased from 2.6 to 13.0 mmol/L. The high K(m) of Brevibacterium resulted in an insensitive reaction and low cholesterol linearity (7.8 mmol/L). An increase in the sample-to-reagent ratio from 1:100 to 1:10 enhanced the reaction rate and the linearity from 7.8 to 20.7 mmol/L. We suggest that Brevibacterium and Streptomyces cholesterol oxidase (with the addition of 3,4 dichlorophenol) are good sources for serum cholesterol determination by the kinetic method.

Metabolic engineering for synthesis of aryl carotenoids in Rhodococcus

Rhodococcus erythropolis naturally synthesizes monocyclic carotenoids: 4-keto-gamma-carotene and gamma-carotene. The genes and the pathway for carotenoid synthesis in R. erythropolis were previously described. We heterologously expressed a beta-carotene desaturase gene (crtU) from Brevibacterium in Rhodococcus to produce aryl carotenoids such as chlorobactene. Expression of the crtU downstream of a chloramphenicol resistance gene on pRhBR171 vector showed higher activity than expression downstream of a native 1-deoxyxylulose-5-phosphate synthase gene (dxs) on pDA71 vector. Expression of the crtU in the beta-carotene ketolase (crtO) knockout Rhodococcus host produced higher purity chlorobactene than expression in the wild-type Rhodococcus host. Growth of the engineered Rhodococcus strain in eight different media showed that nutrient broth yeast extract medium supplemented with fructose gave the highest total yield of chlorobactene. This medium was used for growing the engineered Rhodococcus strain in a 10-l fermentor, and approximately 18 mg of chlorobactene was produced as the almost exclusive carotenoid by fermentation.

Microbial synthesis of triacetic acid lactone

Native g2ps1-encoded 2-pyrone synthase (2-PS) from Gerbera hybrida, a mutant Brevibacterium ammoniagenes fatty acid synthase B (FAS-B) and two different mutants of Penicillium patulum 6-methylsalycilic acid synthase (6-MSAS) are examined to identify the best enzyme to recruit for the microbial synthesis of triacetic acid lactone (TAL). To identify the best microbial host for these evaluations, the native TAL-synthesizing activity of g2ps1-encoded 2-PS is expressed in recombinant Escherichia coli and Saccharomyces cerevisiae constructs. Five-fold higher expression levels of 2-PS are observed in S. cerevisiae. Consequently, microbial synthesis of TAL focuses on S. cerevisiae constructs. Comparison of different promoters for the expression of g2ps1 in S. cerevisiae indicates that the alcohol dehydrogenase II promoter (P(ADH2)) affords the highest expression levels of 2-PS. As a result, the genes encoding the various TAL-synthesizing enzyme activities are expressed in S. cerevisiae from a P(ADH2) promoter. To extend TAL-synthesizing activity beyond g2ps1-encoded 2-PS, the ketoreductase domains of fasB-encoded FAS-B and 6-MSAS-encoded 6-MSAS are modified using a single mutation. Modification of the nicotinamide cofactor-binding site of 6-MSAS with a triple mutation is also examined. Separate S. cerevisiae constructs expressing native g2ps1, mutant Y2226F fasB, mutant Y1572F 6-MSAS, and mutant G1419A-G1421P-G1424A 6-MSAS are cultured under the same fermentor-controlled conditions. The highest concentration (1.8 g/L) and yield (6%) of TAL are synthesized from glucose by S. cerevisiae expressing the Y1572F mutant of 6-MSAS.

Purification and characterization of the alcohol dehydrogenase with a broad substrate specificity originated from 2-phenylethanol-assimilating Brevibacterium sp. KU 1309

A novel 2-phenylethanol dehydrogenase has been purified from a soil bacterium Brevibacterium sp. KU 1309. The enzyme was purified about 1400-fold to homogeneity, and found to be a monomeric enzyme of apparent 39 kDa. The enzyme had broad substrate specificity and catalyzes a reversible oxidation of various primary alcohols to aldehydes. The enzyme required NAD+, but not NADP+ as a cofactor. Thus, the enzyme was classified into a group of NAD+-dependent primary alcohol dehydrogenase. The activity was inhibited by Cu2+, Ni2+, Ba2+, Hg2+ and p-chloromercuribenzoate. The enzyme is expected to be applicable as an effective biocatalyst in the oxidation of various alcohols.

Aromatic ring cleavage by homoprotocatechuate 2,3-dioxygenase: role of His200 in the kinetics of interconversion of reaction cycle intermediates

Homoprotocatechuate 2,3-dioxygenase (WT 2,3-HPCD) isolated from Brevibacterium fuscum utilizes an active site Fe(II) and O(2) to catalyze proximal extradiol cleavage of the aromatic ring of the substrate (HPCA). Here, the conserved active site residue His200 is changed to Gln, Glu, Ala, Asn, and Phe, and the reactions of the mutant enzymes are probed using steady-state and transient kinetic techniques. Each mutant catalyzes ring cleavage of HPCA to yield the normal product. H200Q and H200N retain 30-40% of the WT 2,3-HPCD activity at 24 degrees C, but the other mutants reduce the k(cat) to less than 9% of normal. The origin of the reduced activity is unlikely to be the substrate binding phase of the catalytic cycle, because the multistep anaerobic binding reaction of the chromophoric substrate 4-nitrocatechol (4NC) is shown to proceed with rate constants similar to those observed for WT 2,3-HPCD. In contrast, the rate constants of several steps in the multistep O(2) binding/insertion and product release half of the reaction cycle are substantially slowed, in particular the steps in which activated oxygen attacks the organic substrate and in which product is released. In the case of the H200N mutant, the product of 4NC oxidation is not the usual ring cleavage product, but rather the 4NC quinone. These results suggest that the main role of His200 is in facilitating the steps in the second half of the reaction cycle. The decreased rate constants for the O(2) insertion steps in the catalytic cycles of the mutant enzymes allow the oxygen adduct of an extradiol dioxygenase to be detected for the first time.

Dissecting the structural determinants of the stability of cholesterol oxidase containing covalently bound flavin

Cholesterol oxidase from Brevibacterium sterolicum is a monomeric flavoenzyme catalyzing the oxidation and isomerization of cholesterol to cholest-4-en-3-one. This protein is a class II cholesterol oxidases, with the FAD cofactor covalently linked to the enzyme through the His(69) residue. In this work, unfolding of wild-type cholesterol oxidase was compared with that of a H69A mutant, which does not covalently bind the flavin cofactor. The two protein forms do not show significant differences in their overall topology, but the urea-induced unfolding of the H69A mutant occurred at significant lower urea concentrations than wild-type (approximately 3 versus approximately 5 M, respectively), and the mutant protein had a melting temperature approximately 10-15 degrees C lower than wild-type in thermal denaturation experiments. The different sensitivity of the various spectroscopic features used to monitor protein unfolding indicated that in both proteins a two-step (three-state) process occurs. The presence of an intermediate was more evident for the H69A mutant at 2 m urea, where catalytic activity and tertiary structure were lost, and new hydrophobic patches were exposed on the protein surface, resulting in protein aggregation. Comparative analysis of the changes occurring upon urea and thermal treatment of the wild-type and H69A protein showed a good correlation between protein instability and the elimination of the covalent link between the flavin and the protein. This covalent bond represents a structural device to modify the flavin redox potentials and stabilize the tertiary structure of cholesterol oxidase, thus pointing to a specific meaning of the flavin binding mode in enzymes that carry out the same reaction in pathogenic versus non-pathogenic bacteria.

Industrial importance of the genus Brevibacterium

The genus Brevibacterium has long been difficult for taxonomists to classify due to its close morphological similarity to other genera. Since it was proposed in 1953, the genus has often been redefined. The genus is best known for its important role in the ripening of certain cheeses (B. linens) and for its supposed over-production of L: -amino acids. Other interesting industrial applications, including the production of ectoine, have recently been proposed. The general characteristics, the occurrence and the recent taxonomy of Brevibacterium are reviewed here. Furthermore, known and potential industrial applications for Brevibacterium species are briefly discussed.

Influence of adjunct cultures on volatile free fatty acids in reduced-fat Edam cheeses

The effects of the adjunct cultures Lactococcus lactis ssp. diacetylactis, Brevibacterium linens BL2, Lactobacillus helveticus LH212, and Lactobacillus reuteri ATCC 23272 on volatile free fatty acid production in reduced-fat Edam cheese were studied. Lipase activity evaluation using p-nitrophenyl fatty acid ester substrates indicated that L. lactis ssp. diacetylactis showed the highest activity among the 4 adjunct cultures. Full-fat and 33% reduced-fat control cheeses (no adjunct) were made along with 5 treatments of reduced-fat cheeses, which included individual, and a mixture of the adjunct cultures. Volatile free fatty acids of cheeses were analyzed using static headspace analysis with 4-bromofluorobenzene as an internal standard. Changes in volatile free fatty acid concentrations were found in headspace gas of cheeses after 3-and 6-mo ripening. Acetic acid was the most abundant acid detected throughout ripening. Full-fat cheese had the highest relative amount of propionic acid among the cheeses. Certain adjunct cultures had a definite role in lipolysis at particular times. Reduced-fat cheese with L. lactis ssp. diacetylactis at 3-mo showed the highest levels of butyric, isovaleric, n-valeric, iso-caproic, and n-caproic acid. Reduced-fat cheese with Lactobacillus reuteri at 6 mo produced the highest relative concentration of isocaproic, n-caproic, and heptanoic, and the highest relative concentration of total acids.

Single-turnover kinetics of homoprotocatechuate 2,3-dioxygenase

Homoprotocatechuate 2,3-dioxygenase isolated from Brevibacterium fuscum utilizes an active site Fe(II) and O(2) to catalyze proximal extradiol cleavage of the substrate aromatic ring. In contrast to other members of the ring cleaving dioxygenase family, the transient kinetics of the extradiol dioxygenase catalytic cycle have been difficult to study because the iron is nearly colorless and EPR silent. Here, it is shown that the reaction cycle kinetics can be monitored by utilizing the alternative substrate 4-nitrocatechol (4NC), which is also cleaved in the proximal extradiol position. Changes in the optical spectrum of 4NC occurring as a result of ionization, environmental changes, and ring cleavage allow both the substrate binding and product formation phases of the reaction to be studied. It is shown that substrate binding occurs in a four-step process probably involving binding to two ionization states of the enzyme at different rates. Following an initial rapid binding of the monoanionic 4NC in the active site, slower binding to the Fe(II) and conversion to the dianionic form occur. The bound dianionic 4NC reacts rapidly with O(2) in four additional steps, apparently occurring in sequence. On the basis of the optical properties of the intermediates, these steps are hypothesized to be O(2) binding to the iron, isomerization of the resulting complex, ring opening, and product release. The natural substrate appears to form the same intermediates but with much larger rate constants. These are the first transient intermediates to be reported for an extradiol dioxygenase reaction.

Production of l-2,3-butanediol by a new pathway constructed in Escherichia coli

AIMS

A metabolic pathway for L-2,3-butanediol (BD) as the main product has not yet been found. To rectify this situation, we attempted to produce L-BD from diacetyl (DA) by producing simultaneous expression of diacetyl reductase (DAR) and L-2,3-butanediol dehydrogenase (BDH) using transgenic bacteria, Escherichia coli JM109/pBUD-comb.

METHODS AND RESULTS

The meso-BDH of Klebsiella pneumoniae was used for its DAR activity to convert DA to L-acetoin (AC) and the L-BDH of Brevibacterium saccharolyticum was used to reduce L-AC to L-BD. The respective gene coding each enzyme was connected in tandem to the MCS of pFLAG-CTC (pBUD-comb). The divided addition of DA as a source, addition of 2% glucose, and the combination of static and shaking culture was effective for the production.

CONCLUSIONS

L-BD (2200 mg l(-1)) was generated from 3000 mg l(-1) added of DA, which corresponded to a 73% conversion rate. Meso-BD as a by-product was mixed by 2% at most.

SIGNIFICANCE AND IMPACT OF THE STUDY

An enzyme system for converting DA to L-BD was constructed with a view to using DA-producing bacteria in the future.

Performance of four sources of cholesterol oxidase for serum cholesterol determination by the enzymatic endpoint method

BACKGROUND

Cholesterol oxidase is used for the determination of serum cholesterol. It can be derived from Streptomyces, Pseudomonas fluorescens, Cellulomonas, and Brevibacterium. This study compared the performance characteristics of four enzymes in the endpoint cholesterol determination.

METHODS

Using the Mega analyzer, we studied assay optimization, linearity, precision, recovery, interference, stability, and compared 110 patient samples.

RESULTS

The linearity for the four enzymes was up to 13.0 mmol/l at the optimal enzyme activity. The average within-run CVs ranged from 1.6% to 1.9% and between-day ranged from 2.8% to 3.0%, within the NCEP analytical criteria. The analytical recoveries obtained from four reagents ( approximately 96.5%) were excellent. The assays using these enzyme sources compared favorably with the commercial method and appeared accurate near the clinical decision cut-points. Hemoglobin concentration at 1.9 g/l interfered with the P. fluorescens cholesterol oxidase. Bilirubin caused a negative interference while lipemia generated a positive interference with all enzyme sources. Reagents were stable up to 6 weeks.

CONCLUSIONS

Streptomyces, Cellulomonas, and Brevibacterium were essentially analytically equivalent. Streptomyces and Cellulomonas cholesterol oxidase are one-quarter as expensive Brevibacterium. Cellulomonas is a new source of cholesterol oxidase for determining serum cholesterol by the endpoint method.

Identification of a gene encoding Lon protease from Brevibacillus thermoruber WR-249 and biochemical characterization of its thermostable recombinant enzyme

A gene encoding thermostable Lon protease from Brevibacillus thermoruber WR-249 was cloned and characterized. The Br. thermoruber Lon gene (Bt-lon) encodes an 88 kDa protein characterized by an N-terminal domain, a central ATPase domain which includes an SSD (sensor- and substrate-discrimination) domain, and a C-terminal protease domain. The Bt-lon is a heat-inducible gene and may be controlled under a putative Bacillus subtilis sigmaA-dependent promoter, but in the absence of CIRCE (controlling inverted repeat of chaperone expression). Bt-lon was expressed in Escherichia coli, and its protein product was purified. The native recombinant Br. thermoruber Lon protease (Bt-Lon) displayed a hexameric structure. The optimal temperature of ATPase activity for Bt-Lon was 70 degrees C, and the optimal temperature of peptidase and DNA-binding activities was 50 degrees C. This implies that the functions of Lon protease in thermophilic bacteria may be switched, depending on temperature, to regulate their physiological needs. The peptidase activity of Bt-Lon increases substantially in the presence of ATP. Furthermore, the substrate specificity of Bt-Lon is different from that of E. coli Lon in using fluorogenic peptides as substrates. Notably, the Bt-Lon protein shows chaperone-like activity by preventing aggregation of denatured insulin B-chain in a dose-dependent and ATP-independent manner. In thermal denaturation experiments, Bt-Lon was found to display an indicator of thermostability value, Tm of 71.5 degrees C. Sequence comparison with mesophilic Lon proteases shows differences in the rigidity, electrostatic interactions, and hydrogen bonding of Bt-Lon relevant to thermostability.

Rational Pathway Engineering of Type I Fatty Acid Synthase Allows the Biosynthesis of Triacetic Acid Lactone from d-Glucose in Vivo

Metabolic pathway engineering is a powerful tool to synthesize structurally diverse and complex chemicals via genetic manipulation of multistep catalytic systems involved in cell metabolism. Here, we report the rational design of a fatty acid biosynthetic pathway, Brevibacterium ammoniagenes fatty acid synthase B (FAS-B), that allows the microbial synthesis of triacetic acid lactone (TAL) from an inexpensive feedstock, d-glucose. TAL can be chemically converted to phloroglucinol, which is a core structure for the synthesis of various high value bioactive compounds and energetic compounds such as 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Synthesis of phloroglucinol from d-glucose using this combined biological and chemical synthesis may offer significant advantages over the current phloroglucinol manufacture, including environmental friendliness and reduction in the cost of phloroglucinol. More importantly, it represents a novel strategy for the benzene-free synthesis of aromatic chemicals.

Conversion of extradiol aromatic ring-cleaving homoprotocatechuate 2,3-dioxygenase into an intradiol cleaving enzyme

The intra- and extradiol subfamilies of catechol-adduct ring-cleaving dioxygenases each exhibit nearly absolute fidelity for the ring cleavage position. This is often attributed to the fact that the oxygen activation mechanism of intradiol dioxygenases utilizes Fe3+ while that of the extradiol enzymes employs Fe2+, but the subfamilies also differ in primary sequence, structural fold, iron ligands, and second sphere active site amino acid residues. Here, we examine the effects of the second sphere residue H200 in the active site of homoprotocatechuate 2,3-dioxygenase (2,3-HPCD), an extradiol-cleaving enzyme. It is shown that the H200F mutant enzyme catalyzes extradiol cleavage of the normal substrate, homoprotocatechuate (HPCA), but intradiol cleavage of the alternative substrate 2,3-dihydroxybenzoate (2,3-DHB) while in the Fe2+ oxidation state. Wild-type 2,3-HPCD catalyzes extradiol cleavage of both substrates. This is the first report of intradiol cleavage by an extradiol dioxygenase. It suggests that intradiol cleavage can occur with the iron in the Fe2+ state, with the iron ligand set characteristic of extradiol dioxygenases, and through a mechanism in which oxygen is activated by binding to the iron rather than directly attacking the substrate as in true intradiol dioxygenases. This indicates that substrate binding geometry and acid/base chemistry of second sphere residues play important roles in determining the course of the dioxygenase reaction.

Cloning and expression of the inorganic pyrophosphatase gene from the amino acid producer Brevibacterium lactofermentum ATCC 13869

A 20-kDa Brevibacterium lactofermentum protein was detected when purifying the His-tagged FtsZBL. The protein was identified by matrix-assisted laser desorption/ionisation time of flight as the inorganic pyrophosphatase encoded by the ppa gene, which is present as a single copy in the genome of Corynebacterium glutamicum. The ppa gene was cloned from B. lactofermentum chromosomal DNA by polymerase chain reaction; it seemed to be an essential gene and it might represent an attractive target for drug discovery. The cloned ppa gene complemented a ppa- Escherichia coli mutant and a ppa-gfp gene fusion revealed that the gene product mainly accumulated at the cell poles in both E. coli and B. lactofermentum.

High cell density cultivation of Brevibacterium linens and formation of proteinases and lipase

Brevibacterium linens forms hydrolytic enzymes which can be used to accelerate the ripening of cheese without causing bitterness. B. linens ATCC 9172 was grown to a high cell density (50 g dry wt l-1 after 60 h) in a mineral medium containing lactic acid, soy-peptone and ammonium sulphate by applying a continuous feed of nutrients. The maximal activities of L-leucine aminopeptidase and cell-associated proteinase were 286 U l-1 and 202 U l-1, respectively. The cell-associated lipolytic activity exhibited a strong and sudden increase at 46 h, resulting in a maximum of 9.5 U g-1 dry wt; thus the volumetric productivity of proteolytic and lipolytic activity was 4220 U l-1 h-1 and 7.3 U l-1 h-1, respectively.

Catabolism of aromatic amino acids in cheese-related bacteria: aminotransferase and decarboxylase activities

Bacterial decarboxylases and aminotransferases may be involved in the production of flavour or off-flavour compounds from aromatic amino acids during cheese ripening. Transamination is one of the first steps in amino acid catabolism for both lactococci and lactobacilli (Gao et al. 1997; Klein et al. 2001). Biologically active amines, produced by decarboxylation, such as tyramine, phenylethylamine, tryptamine, histamine, cadaverine and putrescine, known as biogenic amines, have been found in cheese and can cause migraine and hypertension in susceptible consumers (McSweeney & Sousa, 2000).

First enantiodivergent Baeyer-Villiger oxidation by recombinant whole-cells expressing two monooxygenases from Brevibacterium

Microbial Baeyer-Villiger oxidations of representative mesomeric ketones with recombinant Escherichia coli cells expressing two monooxygenases from Brevibacterium were investigated. The two enzymes displayed enantiodivergent biotransformations on an array of structurally diverse substrates, allowing access to some key lactone intermediates in natural compound synthesis.

Purification and properties of a new Brevibacterium sterolicum cholesterol oxidase produced by E. coli MM294/pnH10

A gene encoding a cholesterol oxidase from Brevibacterium sterolicum nov. sp. ATCC21387 was isolated by an expression cloning method and highly expressed by a recombinant strain Escherichia coli MM294/pnH10. The purified cholesterol oxidase was a typical flavoprotein with a molecular mass of 46.5 kDa, absorption peaks at 280, 360, and 450 nm. Optimum pH and temperature were found at pH 6.5 and 55 degrees C, respectively. The enzyme acted on 3beta-hydroxysteroids such as cholesterol, pregnenolone, and beta-sitosterol at high rates, but on dehydro-epi-androsterone to a lesser degree. The molecular and catalytic properties were different from those of cholesterol oxidase I, which was initially discovered in B. sterolicum nov. sp. ATCC21387. The new enzyme, designated cholesterol oxidase II, was distinguished by its high affinity toward cholesterol (K(m)=30 microM).

Construction of a xylanase-producing strain of Brevibacterium lactofermentum by stable integration of an engineered xysA gene from Streptomyces halstedii JM8

A xylanolytic strain of Brevibacterium lactofermentum containing the Streptomyces halstedii His-tagged xysA gene was generated. The new strain contains DNA derived from S. halstedii, expresses xylanolytic activity, and was obtained by an integrative process mediated by a conjugative plasmid targeted to a dispensable chromosomal region located downstream from the essential cell division gene ftsZ. The His-tagged Xys1 enzyme was constitutively expressed under the control of the kan promoter from Tn5 and was easily purified by use of Ni-nitrilotriacetic acid-agarose. The new strain is stable for more than 200 generations, lacks any known antibiotic resistance gene, and does not need any selective pressure to maintain the integrated gene. This strategy can be used to integrate any gene into the B. lactofermentum chromosome and to maintain it stably without the use of antibiotics for selection.

Expression of the genes coding for the xylanase Xys1 and the cellulase Cel1 from the straw-decomposing Streptomyces halstedii JM8 cloned into the amino-acid producer Brevibacterium lactofermentum ATCC13869

The xylanase ( xysA) and the cellulase ( celA1) genes from Streptomyces halstedii JM8 were cloned into Escherichia coli/ Brevibacterium lactofermentum shuttle vectors and successfully expressed in both hosts when placed downstream from the kanamycin resistance promoter (Pkan) from Tn 5 but not when under the control of their own promoters. Xylanase was secreted into the culture media of B. lactofermentum by removal of the same leader peptide as is removed in S. halstedii. The main difference between the production of xylanase by Streptomyces and corynebacteria was the low level of processing of the mature extracellular xylanase by B. lactofermentum, probably due to the lack of protease activity in this microorganism.

Influence of adjunct cultures on ripening of reduced fat Edam cheeses

The influence of four adjunct cultures [Brevibacterium linens (BL2), Lactococcus lactis ssp. diacetylactis, Lactobacillus helveticus (LH212), and Lactobacillus reuteri (ATCC 23272)] on chemical and sensory characteristics of reduced fat Edam cheese was studied. The aminopeptidase activity of Lactococcus lactis ssp. diacetylactis was higher than that of Lactobacillus helveticus, Lactobacillus reuteri, and Brevibacterium linens, respectively. Mean percent fat and moisture contents of reduced fat cheese were 20.85 +/- 0.69 and 42.95 +/- 0.43, respectively. Percentage of fat and moisture of full fat control cheese were 30.06 +/- 0.78 and 39.11 +/- 0.60. Titratable acidity increased in all cheese with aging while pH initially decreased but increased in cheese after 6 mo aging at 7 degrees C. Lactic acid bacteria counts were on average one log higher for reduced fat cheeses than for full fat control cheese and counts decreasing with aging. Free amino acids (FAA) in cheeses increased with aging, and were higher in reduced fat cheeses than in the full fat control cheese. Reduced fat cheeses containing L. helveticus exhibited the highest FAA content. Descriptive sensory panelists (n = 9) did not detect differences among cheeses after 3 and 6 mo ripening, but aged/developed flavors (fruity, nutty, brothy, sulfur, free fatty acid) and sweetness increased between 3 and 6 mo. Expert panelists (n = 6) detected differences in texture quality among the cheeses. Reduced fat control cheeses and reduced fat cheeses with L. helveticus and L. reuteri received the highest texture quality scores. Addition of L. helveticus and Lc. lactis ssp. diacetylactis, as adjunct cultures to reduced fat Edam cheeses increased proteolysis, while the addition of L. helveticus and L. reuteri increased texture quality of cheeses.

Oxygen access to the active site of cholesterol oxidase through a narrow channel is gated by an Arg-Glu pair

Cholesterol oxidase is a monomeric flavoenzyme that catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. Two forms of the enzyme are known, one containing the cofactor non-covalently bound to the protein and one in which the cofactor is covalently linked to a histidine residue. The x-ray structure of the enzyme from Brevibacterium sterolicum containing covalently bound FAD has been determined and refined to 1.7-A resolution. The active site consists of a cavity sealed off from the exterior of the protein. A model for the steroid substrate, cholesterol, can be positioned in the pocket revealing the structural factors that result in different substrate binding affinities between the two known forms of the enzyme. The structure suggests that Glu(475), located at the active site cavity, may act as the base for both the oxidation and the isomerization steps of the catalytic reaction. A water-filled channel extending toward the flavin moiety, inside the substrate-binding cavity, may act as the entry point for molecular oxygen for the oxidative half-reaction. An arginine and a glutamate residue at the active site, found in two conformations are proposed to control oxygen access to the cavity from the channel. These concerted side chain movements provide an explanation for the biphasic mode of reaction with dioxygen and the ping-pong kinetic mechanism exhibited by the enzyme.

Purification and characterization of L-2,3-butanediol dehydrogenase of Brevibacterium saccharolyticum C-1012 expressed in Escherichia coli

The L-2,3-butanediol dehydrogenase produced in E. coli JM109/pLBD2-CTC was purified by 5 steps. The molecular mass of this enzyme was estimated at 110 kDa and the subunit was measured to be 30 kDa. The L-BDH had some differences from the BDHs from other sources in substrate specificity, pI value, pH stability, effects of divalent cations, and organic acids.

Tryptophan catabolism in Brevibacterium linens as a potential cheese flavor adjunct

Attempts to develop a desirable reduced fat Cheddar cheese are impeded by a propensity for flavor defects such as meaty-brothy, putrid, fecal, and unclean off-flavors in these products. Recent studies suggest aromatic amino acid catabolism of starter, adjunct, and nonstarter lactic acid bacteria significantly impact off-flavor development. The objective of this study was to delineate pathways for catabolism of tryptophan (Trp) in Brevibacterium linens, a cheese flavor adjunct, and to determine the potential for this organism to contribute to this defect. Growth and production of aromatic compounds from Trp by B. linens BL2 were compared in two incubated conditions (laboratory and a cheese-like environment). A chemically defined medium was used to determine the cellular enzymes and metabolites involved in Trp catabolism. Trp was converted to kynurenine, anthranilic acid, and three unknown compounds in laboratory conditions. The accumulation of other unknown compounds in the culture supernatant in laboratory conditions indicated that B. linens BL2 degraded Trp by various routes. Up to 65% of Trp was converted to anthranilic acid via the anthranilic acid pathway. To assess this potential before cheese making, the cells were incubated in cheese-like conditions (15 degrees C, pH 5.2, no sugar source, 4% NaCl). Trp was not utilized by BL2 incubated in this condition. Enzyme studies using cell-free extracts of cells incubated in laboratory conditions and assayed at optimal and nonoptimal enzyme assay conditions revealed Trp transaminase (EC 2.6.1.27) was active before enzymes of the anthranilic acid pathway were detected. The products of Trp transaminase activity were not, however, found in the culture supernatant, indicating these intermediates were not exported nor accumulated by the cells. Enzymes assayed in nonoptimal conditions had considerably lower enzyme activities than found in laboratory incubation conditions. Based on these results, we hypothesize that these enzymes are not likely to be involved in the formation of compounds associated with off-flavors in Cheddar cheese.

Cholesterol oxidase from Brevibacterium sterolicum. The relationship between covalent flavinylation and redox properties

Brevibacterium sterolicum possesses two forms of cholesterol oxidase, one containing noncovalently bound FAD, the second containing a FAD covalently linked to His(69) of the protein backbone. The functional role of the histidyl-FAD bond in the latter cholesterol oxidase was addressed by studying the properties of the H69A mutant in which the FAD is bound tightly, but not covalently, and by comparison with native enzyme. The mutant retains catalytic activity, but with a turnover rate decreased 35-fold; the isomerization step of the intermediate 3-ketosteroid to the final product is also preserved. Stabilization of the flavin semiquinone and binding of sulfite are markedly decreased, this correlates with a lower midpoint redox potential (-204 mV compared with -101 mV for wild-type). Reconstitution with 8-chloro-FAD led to a holoenzyme form of H69A cholesterol oxidase with a midpoint redox potential of -160 mV. In this enzyme form, flavin semiquinone is newly stabilized, and a 3.5-fold activity increase is observed, this mimicking the thermodynamic effects induced by the covalent flavin linkage. It is concluded that the flavin 8alpha-linkage to a (N1)histidine is a pivotal factor in the modulation of the redox properties of this cholesterol oxidase to increase its oxidative power.

Stereochemical applications of the expression of the L-2,3-butanediol dehydrogenase gene in Escherichia coli

The L-2,3-butanediol dehydrogenase (L-BDH) gene of Brevibacterium saccharolyticum was strongly expressed in Escherichia coli using the tac promoter. However, the stereospecificity of the resulting L-BDH was reduced. The region upstream of the meso-BDH gene of Klebsiella pneumoniae was also involved in the expression of the B. saccharolyticum gene. However, in this case, the resulting L-BDH exhibited more stable stereospecificity. A stereospecificity recognition region was located within the rear sequence (Hpa I site, carboxy terminal) of the BDH open reading frame. Using a transformed strain of E. coli, the conversion of L-acetoin (L-AC), in the commercially available racemic mixture of AC, to L-2,3-butanediol (L-BD) was attempted. As a result, 0.37% L-BD was formed from 1% AC added to the culture.

A rate-limiting conformational change of the flavin in p-hydroxybenzoate hydroxylase is necessary for ligand exchange and catalysis: studies with 8-mercapto- and 8-hydroxy-flavins

The FAD of p-hydroxybenzoate hydroxylase (PHBH) is known to exist in two conformations. The FAD must be in the in-position for hydroxylation of p-hydroxybenzoate (pOHB), whereas the out-position is essential for reduction of the flavin by NADPH. In these investigations, we have used 8-mercapto-FAD and 8-hydroxy-FAD to probe the movement of the flavin in catalysis. Under the conditions employed, 8-mercapto-FAD (pK(a) = 3.8) and 8-hydroxy-FAD (pK(a) = 4.8) are mainly anionic. The spectral characteristics of the anionic forms of these flavins are very sensitive to their environment, making them sensitive probes for detecting movement of the flavin during catalysis. With these flavin analogues, the enzyme hydroxylates pOHB efficiently, but at a rate much slower than that of enzyme with FAD. Reaction of oxygen with reduced forms of these modified enzymes in the absence of substrate appears to proceed through the formation of the flavin-C4a-hydroperoxide intermediate, as with normal enzyme, but the decay of this intermediate is so fast compared to its formation that very little accumulates during the reaction. However, after elimination of H2O2 from the flavin-C4a-hydroperoxide, a perturbed oxidized enzyme spectrum is observed (Eox*), and this converts slowly to the spectrum of the resting oxidized form of the enzyme (Eox). In the presence of pOHB, PHBH reconstituted with 8-mercapto-FAD also shows the additional oxidized intermediate (Eox*) after the usual oxygenated C4a-intermediates have formed and decayed in the course of the hydroxylation reaction. This Eox* to Eox step is postulated to be due to flavin movement. Furthermore, binding of pOHB to resting (Eox) follows a three-step equilibrium mechanism that is also consistent with flavin movement being the rate-limiting step. The rate for the slowest step during pOHB binding is similar to that observed for the conversion of Eox* to Eox during the oxygen reaction in the absence or presence of substrate. Steady-state kinetic analysis of PHBH substituted with 8-mercapto-FAD demonstrated that the apparent k(cat) is also similar to the rate of Eox* conversion to Eox. Presumably, the protein environment surrounding the flavin in Eox* differs slightly from that of the final resting form of the enzyme (Eox).

Use of the parallax-quench method to determine the position of the active-site loop of cholesterol oxidase in lipid bilayers

To elucidate the cholesterol oxidase-membrane bilayer interaction, a cysteine was introduced into the active site lid at position-81 using the Brevibacterium enzyme. To eliminate the possibility of labeling native cysteine, the single cysteine in the wild-type enzyme was mutated to a serine without any change in activity. The loop-cysteine mutant was then labeled with acrylodan, an environment-sensitive fluorescence probe. The fluorescence increased and blue-shifted upon binding to lipid vesicles, consistent with a change into a more hydrophobic, i.e., lipid, environment. This acrylodan-labeled cholesterol oxidase was used to explore the pH, ionic strength, and headgroup dependence of binding. Between pH 6 and 10, there was no significant change in binding affinity. Incorporation of anionic lipids (phosphatidylserine) into the vesicles did not increase the binding affinity nor did altering the ionic strength. These experiments suggested that the interactions are primarily driven by hydrophobic effects not ionic effects. Using vesicles doped with either 5-doxyl phosphatidylcholine, 10-doxyl phosphatidylcholine, or phosphatidyl-tempocholine, quenching of acrylodan fluorescence was observed upon binding. Using the parallax method of London [Chattopadhyay, A., and London, E. (1987) Biochemistry 26, 39-45], the acrylodan ring is calculated to be 8.1 +/- 2.5 A from the center of the lipid bilayer. Modeling the acrylodan-cysteine residue as an extended chain suggests that the backbone of the loop does not penetrate into the lipid bilayer but interacts with the headgroups, i.e., the choline. These results demonstrate that cholesterol oxidase interacts directly with the lipid bilayer and sits on the surface of the membrane.

Trehalose synthesis by sequential reactions of recombinant maltooligosyltrehalose synthase and maltooligosyltrehalose trehalohydrolase from Brevibacterium helvolum

A DNA fragment encoding two enzymes leading to trehalose biosynthesis, maltooligosyltrehalose synthase (BvMTS) and maltooligosyltrehalose trehalohydrolase (BvMTH), was cloned from the nonpathogenic bacterium Brevibacterium helvolum. The open reading frames for the two proteins are 2,331 and 1,770 bp long, respectively, and overlap by four nucleotides. Recombinant BvMTS, BvMTH, and fusion gene BvMTSH, constructed by insertion of an adenylate in the overlapping region, were expressed in Escherichia coli. Purified BvMTS protein catalyzed conversion of maltopentaose to maltotriosyltrehalose, which was further hydrolyzed by BvMTH protein to produce trehalose and maltotriose. The enzymes shortened maltooligosaccharides by two glucose units per cycle of sequential reactions and released trehalose. Maltotriose and maltose were not catalyzed further and thus remained in the reaction mixtures depending on whether the substrates had an odd or even number of glucose units. The bifunctional in-frame fusion enzyme, BvMTSH, catalyzed the sequential reactions more efficiently than an equimolar mixture of the two individual enzymes did, presumably due to a proximity effect on the catalytic sites of the enzymes. The recombinant enzymes produced trehalose from soluble starch, an abundant natural source for trehalose production. Addition of alpha-amylase to the enzyme reaction mixture dramatically increased trehalose production by partial hydrolysis of the starch to provide more reducing ends accessible to the BvMTS catalytic sites.

Behavior of Brevibacterium linens and Debaryomyces hansenii as ripening flora in controlled production of soft smear cheese from reconstituted milk: protein degradation

Model smear soft cheeses, prepared with Debaryomyces hansenii and Brevibacterium linens as ripening starters, were ripened under aseptic conditions. Results of the cheese-making trials, in triplicate, were similar and showed similar patterns of protein degradation. In all of the trials, the acid-soluble nitrogen and nonprotein nitrogen (NPN) indexes and NH3 concentrations of the rind were low until d 10. The acid-soluble nitrogen and NPN of the rind then increased to 100 and 18% of total nitrogen, respectively, at d 76. The NH3 concentrations remained low until d 24 and increased until d 70, reaching about 1.8 g of NH3/kg of DM, and then remained constant. The acid-soluble nitrogen and NPN indexes and NH3 concentrations in the inner cheese mass were lower than in the rind. They showed the same evolution, reaching about 18% for acid-soluble nitrogen, 10% for NPN, and 1.5 g of NH3/kg of DM. It was shown that the inner cheese pH and populations of D. hansenii and B. linens have an effect on proteolysis. Viable cell counts of D. hansenii and B. linens were correlated with the environmental conditions and with proteolytic products. The determining role of carbon source and NH3 diffusions on the cheese ripening process were confirmed.

Development of an improved assay for purine nucleoside kinase activity in cell extracts and detection of inosine kinase activity in Brevibacterium acetylicum ATCC 953, related species, and Corynebacterium flaccumfaciens ATCC 6887

An improved assay was developed to detect direct purine nucleoside phosphorylating activity in cell-free extracts. Direct inosine phosphorylating activity was detected in 2 of 70 species tested. Both activities, which depended on magnesium ion and ATP, phosphorylated a hydroxyl group at the 5' position of inosine. The new assay was shown to be useful for screening of direct purine nucleoside phosphorylating activity and have the potential to detect inosine kinase in the presence of a background of nucleoside phosphorylase and purine phosphoribosyltransferase activities. Previously, the latter two activities made it difficult to correctly detect direct phosphorylation of inosine by inosine kinase.

Cholesterol oxidase: sources, physical properties and analytical applications

Since Flegg (H.M. Flegg, An investigation of the determination of serum cholesterol by an enzymatic method, Ann. Clin. Biochem. 10 (1973) 79-84) and Richmond (W. Richmond, The development of an enzymatic technique for the assay of cholesterol in biological fluids, Scand. J. clin. Lab. Invest. 29 (1972) 25; W. Richmond, Preparation and properties of a bacterial cholesterol oxidase from Nocardia sp. and its application to enzyme assay of total cholesterol in serum, Clinical Chemistry 19 (1973) 1350-1356) first illustrated the suitability of cholesterol oxidase (COD) for the analysis of serum cholesterol, COD has risen to become the most widely used enzyme in clinical laboratories with the exception of glucose oxidase (GOD). The use is widespread because assays incorporating the enzyme are extremely simple, specific, and highly sensitive and thus offer distinct advantages over the Liebermann-Burchard analytical methodologies which employ corrosive reagents and can be prone to unreliable results due to interfering substances such as bilirubin. Individuals can now readily determine their own serum cholesterol levels with a simple disposable test kit. This review discusses COD in some detail and includes the topics: (1) The variety of bacterial sources available; (2) The various extraction/purification protocols utilised in order to obtain protein of sufficient clarification (purity) for use in food/clinical analysis; (3) Significant differences in the properties of the individual enzymes; (4) Substrate specificities of the various enzymes; (5) Examples of biological assays which have employed cholesterol oxidase as an integral part of the analysis, and the various assay protocols; (6) New steroidal products of COD. This review is not a comprehensive description of published work, but is intended to provide an account of recent and current research, and should promote further interest in the application of enzymes to analytical selectivity.

A carotenogenic gene cluster from Brevibacterium linens with novel lycopene cyclase genes involved in the synthesis of aromatic carotenoids

The carotenogenic (crt) gene cluster from Brevibacterium linens, a member of the commercially important group of coryneform bacteria, was cloned and identified. An expression library of B. linens genes was constructed and a fragment of the crt cluster was obtained by functional complementation of a colourless B. flavum mutant, screening transformed cells for production of a yellow pigment. Subsequent screening of a cosmid library resulted in the cloning of the whole crt cluster from B. linens. All genes necessary for the synthesis of the aromatic carotenoid isorenieratene were identified on the basis of sequence homologies. In addition a novel type of lycopene cyclase was identified by complementation of a lycopene-accumulating B. flavum mutant. Two genes, named crt Yc and crt Yd, which code for polypeptides of 125 and 107 amino acids, respectively, are necessary to convert lycopene to beta-carotene. The amino acid sequences of these polypeptides show no similarity to any of the known lycopene cyclases. This is the first example of a carotenoid biosynthetic conversion in which two different gene products are involved, probably forming a heterodimer.

An investigation into the electro-physical characteristics of microbial cells during the metabolism of toxic compounds under conditions of limited O2 availability

The purpose of the work reported here was to experimentally clarify the interconnection between changes in the electro-physical characteristics of microbial suspensions and processes of the metabolism of certain toxic compounds (acrylamide and p-nitrophenol (PNP)) in cells containing enzyme systems of the initial metabolism of these compounds. In this work, we used cells of two strains, Acinetobacter calcoaceticum A-122 and Brevibacterium sp. 13PA, which are capable of utilising PNP and acrylamide, respectively, as the sole source of carbon. Suspensions of these cells exhibited appreciable decreases in the magnitude of the electro-optical signal when the microbial metabolism of PNP and acrylamide was inhibited under conditions of limited O2 supply. This attests to a relationship between the electro-physical characteristics of microbial suspensions and cellular metabolic reactions and also to the negligibly small effect that the non-specific interaction of substrate with the cells has on the suspensions' electro-optical properties.