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PubMed1994

Molecular characterization of microbial alcohol dehydrogenases.

There is an astonishing array of microbial alcohol oxidoreductases. They display a wide variety of substrate specificities and they fulfill several vital but quite different physiological functions. Some of these enzymes are involved in the production of alcoholic beverages and of industrial solvents, others are important in the production of vinegar, and still others participate in the degradation of naturally occurring and xenobiotic aromatic compounds as well as in the growth of bacteria and yeasts on methanol. They can be divided into three major categories. (1) The NAD- or NADP-dependent dehydrogenases. These can in turn be divided into the group I long-chain (approximately 350 amino acid residues) zinc-dependent enzymes such as alcohol dehydrogenases I, II, and III of Saccharomyces cerevisiae or the plasmid-encoded benzyl alcohol dehydrogenase of Pseudomonas putida; the group II short-chain (approximately 250 residues) zinc-independent enzymes such as ribitol dehydrogenase of Klebsiella aerogenes; the group III "iron-activated" enzymes that generally contain approximately 385 amino acid residues, such as alcohol dehydrogenase II of Zymomonas mobilis and alcohol dehydrogenase IV of Saccharomyces cerevisiae, but may contain almost 900 residues in the case of the multifunctional alcohol dehydrogenases of Escherichia coli and Clostridium acetobutylicum. The aldehyde/alcohol oxidoreductase of Amycolatopsis methanolica and the methanol dehydrogenases of A. methanolica and Mycobacterium gasti are 4-nitroso-N,N-dimethylaniline-dependent nicotinoproteins. (2) NAD(P)-independent enzymes that use pyrroloquinoline quinone, haem or cofactor F420 as cofactor, exemplified by methanol dehydrogenase of Paracoccus denitrificans, ethanol dehydrogenase of Acetobacter and Gluconobacter spp. and the alcohol dehydrogenases of certain archaebacteria. (3) Oxidases that catalyze an essentially irreversible oxidation of alcohols, such as methanol oxidase of Hansenula polymorpha and probably the veratryl alcohol oxidases of certain fungi involved in lignin degradation. This review deals mainly with those enzymes for which complete amino acid sequences are available. The discussion focuses on a comparison of their primary, secondary, tertiary, and quaternary structures and their catalytic mechanisms. The physiological roles of the enzymes and isoenzymes are also considered, as are their probable evolutionary relationships.

Alcohol Dehydrogenase↗

PubMed1999

Purification and enzymic properties of the fructosyltransferase of Streptococcus salivarius ATCC 25975.

The recombinant fructosyltransferase (Ftf) of Streptococcus salivarius was expressed in Escherichia coli and purified to electrophoretic homogeneity after a combination of adsorption, ion-exchange and gel-filtration chromatography. The N-terminal signal sequence of the Ftf was removed by E. coli at the same site as in its natural host. The purified Ftf exhibited maximum activity at pH 6.0 and 37 degrees C, was activated by Ca2+, but inhibited by the metal ions Cu2+, Zn2+, Hg2+ and Fe3+. The enzyme catalysed the transfer of the fructosyl moiety of sucrose to a number of acceptors, including water, glucose and sucrose via a Ping Pong mechanism involving a fructosyl-enzyme intermediate. While this mechanism of catalysis is utilized by the levansucrases of Bacillus subtilis and Acetobacter diazotrophicus and the values of the kinetic constants for the three enzymes are similar, sucrose was a far more efficient fructosyl-acceptor for the Ftf of S. salivarius than for the two other enzymes.

Escherichia coli↗

PubMed2004

Development and testing of a novel biosynthesized XCell for treating chronic wounds.

Biosynthesized cellulose is produced by the bacteria, Acetobacter xylinum, and possesses unique properties not present in other biomaterials. The material is formed during fermentation having a multi-layered structure composed of fine, nonwoven, cellulose hydrophilic fibers. This structure allows biosynthesized cellulose to have a high-fluid capacity, superior strength, and biocompatibility, which makes it suitable for topical and implantable biomedical applications. Initial product development of biosynthesized cellulose has focused on advanced wound-care applications. The product, XCell (Xylos Corporation, Langhorne, PA, USA), has been bioengineered to have the ability to both donate and absorb moisture, depending on the wound environment. Comparative bench testing has shown that XCell is the only wound dressing with this unique dual-fluid-handling capability. The product has been studied thoroughly using animal models and proved to be safe and biocompatible. Human clinical testing has demonstrated its effectiveness in providing a moist environment, essential to treating hard-to-heal chronic wounds. The major clinical benefits of the product include: 1) help in removal of non-viable tissue and promotion of autolytic debridement, which results in increased granulation tissue; 2) cleansing of wound margins that leads to epithelial migration and reduction of wound size; and 3) healing of various types of chronic wounds.

Bandages, Hydrocolloid↗

PubMedDate not supplied

Manufacture of a beverage from cheese whey using a "tea fungus" fermentation.

Kombucha is a sour beverage reported to have potential health effects prepared from the fermentation of black tea and sugar with a "tea fungus", a symbiotic culture of acetic acid bacteria and yeasts. Although black tea is the preferred substrate for Kombucha fermentation, other beverages have also been tested as substrates with fair results. Cheese whey is a by-product with a good amount of fermentable lactose that has been used before in the production of beverages, so the objective of this study was to test three types of whey (fresh sweet, fresh acid and reconstituted sweet) in the elaboration of a fermented beverage using a kombucha culture as inoculum. The isolation and identification of bacteria and yeasts from the fermented tea and wheys was done along with the study of the rates of change in sugar consumption, acid production and pH decrease. Several species of acetic acid bacteria (Acetobacter aceti subsp. aceti, Gluconobacter oxydans subsp. industrius, subsp. oxydans and Gluconoacetobacter xylinus) were isolated from the different kombuchas along with the yeasts Saccharomyces cerevisiae, Kluyveromyces marxianus, and Brettanomyces bruxelensis. The main metabolic products in the fermented wheys included ethanol, lactic and acetic acids. A good growth was obtained in both sweet wheys in which a pH of 3.3 and a total acid content (mainly lactic and acetic acids) of 0.07 mol/l was reached after 96 h. The sweet whey fermented beverages contained a relatively low lactose concentration (< 12 g/l). The final ethanol content was low (5 g/l) in all the fermented wheys. The whey products were strongly sour and salty non sparkling beverages.

Acetobacteraceae↗

PubMed1989

A fast spheroplast formation procedure in some 2,5-diketo-D-gluconate- and 2-keto-L-gulonate- producing bacteria.

Calcium 2-keto-L-gulonate (Ca-2-KLG, a key intermediate in vitamin C synthesis) is produced from calcium 2,5-diketo D-gluconate (Ca-2,5-DKG) by a variety of bacteria. A few bacterial species which efficiently convert glucose to Ca-2,5-DKG have been isolated in our laboratory. Our bacterial collection included species that possess the genes for production of Ca-2-KLG from Ca-2,5-DKG; however, the yield of the former is poor. A procedure for the preparation of spheroplasts in Ca-2,5-DKG- and Ca-2-KLG-producing bacteria was developed for the construction of recombinants (fusants), combining the genes for conversion of glucose to Ca-2-KLG efficiently by protoplast fusion. The standard procedure for spheroplast formation in Gram negative bacteria by the Tris-sucrose-EDTA-lysozyme system did not work in the organisms under investigation. The need for an alternative method was necessary. Our results show that, while the Tris-NaCl-EDTA-lysozyme system (pH 8.3) worked very well with bacterial strains of Gluconobacter oxydans (ATCC9937) and Acetobacter melanogenus (NCIM2259), the Tris-sucrose-EDTA-lysozyme system worked well for Erwinia herbicola (ATCC21998), Pseudomonas chlororaphis (NCIM2041) and Corynebacterium species (ATCC31090). However, none of these systems produced spheroplasts in Brevibacterium ketosoreductum (ATCC21914), for which a separate system is under development.

Bacteria↗

PubMedDate not supplied

[Preservation of lyophilized cultures of saprophytic microorganisms].

All of the tested saprophytic microbial cultures remained viable upon 11--16 years of storage in the lyophilized state at 3--6 degrees. The cultures belonged to the following taxonomic groups: Acetobacter, Achromobacter, Azotobacter, Bacillus, Chromatium, Escherichia, Flavobacterium, Lactobacillus, Micrococcus, Proteus, Propionibacterium, Pseudomonas, Rhizobium, Sarcina, Serratia, Streptococcus, Torula, Mycobacterium, Actinomyces. The number of viable cells in the tubes decredased only slightly within this time and remained at the same level as immediately after lyophilization.

Bacterial Physiological Phenomena↗

PubMed1994

Structure-function studies on the ubiquinol oxidation site of the cytochrome bo complex from Escherichia coli using p-benzoquinones and substituted phenols.

To characterize the structural features of the quinol oxidation site (the QL site) of the cytochrome bo complex, a heme-copper respiratory oxidase in Escherichia coli, we carried out structure-inhibitory potency analyses using 7 p-benzoquinones and 33 substituted phenols. Their effects on its ubiquinol-1 oxidase activity were compared with those on the cytochrome bd complex in E. coli and on cytochromes o and alpha 1 in Acetobacter aceti. They showed similar structural properties of the QL site, although cytochrome o was more sensitive to 4-cyanophenols, suggesting a specific interaction of the hydrogen bond-accepting cyano group with the binding pocket. Replacing one of the methyl groups of 2,6-dimethyl-p-benzoquinone, which is the most potent competitive inhibitor, with an ethyl group markedly decreased the inhibitory activity, indicating that the QL site specifically recognizes one C = O group with two methyl groups as the ortho-substituents. In substituted phenols, ortho-chlorine substituents were the most effective in recognition, and the electron-withdrawing ability of the para-substituent determined an inhibitory potency, probably by stabilizing an anionic form. Based on these observations, we postulate that the QL site of the cytochrome bo complex asymmetrically recognizes exogenous ligands and that this property accounts for the sequential electron transfer from ubiquinols to the low-spin heme.

Benzoquinones↗

PubMed1993

Triggering of cellulase biosynthesis by cellulose in Trichoderma reesei. Involvement of a constitutive, sophorose-inducible, glucose-inhibited beta-diglucoside permease.

We prepared [U-14C]cellobiose by cultivating Acetobacter pasteurianus in the presence of [U-14C]glucose and hydrolyzing the [U-14C]cellulose formed with beta-glucosidase-free cellulase from Trichoderma reesei. This 14C-labeled cellobiose was used to investigate the presence of an uptake system for cellobiose in T. reesei. Evidence was obtained for the presence of a high affinity (Km for cellobiose 0.3 microM) but low activity (2.5 milliunits/mg fungal dry weight) cellobiose permease. The permease is formed constitutively, but higher levels are formed after addition of sophorose (glucosyl-beta-1,2-diglucoside), a reputed cellulase inducer. The permease appears to be specific for beta-diglucosides, as the uptake of [U-14C]cellobiose is inhibited by sophorose, gentiobiose (glucosyl-beta-1,3-glucoside), and cellobiose. Under these conditions, cellooligodextrines (n, 4-7; final concentration, 1 mM) are not inhibitors. Glucose, but no other monosaccharides, inhibits the permease. The hypersecretory mutant T. reesei RUT C-30 exhibits elevated permease activities, whereas in T. reesei QM 9979, a mutant strain defective in the induction of cellulases by cellulose or sophorose, strongly reduced permease activities were demonstrated. The results stress a hitherto not recognized point of control in the induction of cellulases by T. reesei at the level of uptake of cellulose oligosaccharides.

Cellulase↗

PubMedDate not supplied