The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

Polyphenols as antimicrobial agents

Degradation of plant cell wall polysaccharides is of major importance in the food and feed, beverage, textile, and paper and pulp industries, as well as in several other industrial production processes. Enzymatic degradation of these polymers has received attention for many years and is becoming a more and more attractive alternative to chemical and mechanical processes. Over the past 15 years, much progress has been made in elucidating the structural characteristics of these polysaccharides and in characterizing the enzymes involved in their degradation and the genes of biotechnologically relevant microorganisms encoding these enzymes. The members of the fungal genus Aspergillus are commonly used for the production of polysaccharide-degrading enzymes. This genus produces a wide spectrum of cell wall-degrading enzymes, allowing not only complete degradation of the polysaccharides but also tailored modifications by using specific enzymes purified from these fungi. This review summarizes our current knowledge of the cell wall polysaccharide-degrading enzymes from aspergilli and the genes by which they are encoded.

Aspergillus Enzymes Involved in Degradation of Plant Cell Wall Polysaccharides

Microbial pectinolytic enzymes: A review

The increased resistance of pathogenic microorganisms is frequently attributed to the extreme and inadequate use of antibiotics and transmission of resistance within and between individuals. To counter the emergence of resistant microorganisms, considerable resources have been invested in the search for new antimicrobials. Plants synthesize a diverse array of secondary metabolites (phytochemicals) known to be involved in defense mechanisms, and in the last few years it is recognized that some of these molecules have health beneficial effects, including antimicrobial properties. In this study, the mechanism of action of gallic (GA) and ferulic (FA) acids, a hydroxybenzoic acid and a hydroxycinnamic acid, was assessed on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes. The targets of antimicrobial action were studied using different bacterial physiological indices: minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), membrane ...

Antibacterial activity and mode of action of ferulic and gallic acids against pathogenic bacteria

A.M. STRASSER DE SAAD AND M.C. MANCA DE NADRA. 1993. Twenty strains of Pediococcus pentosaceus isolated from wine were examined for production of bacteriocins. Only two of them showed inhibitory activity, Ped. pentosaceus N4p against the indicator strains of the same species and N5p against 19 strains of the three genera of lactic acid bacteria from wine. The antimicrobial substance from N5p strains was removed by membrane (0.2 μm) filtration, destroyed by organic solvents and proteolytic enzymes. It was stable for 60 min at 100dC. The bacteriocin was produced early in the growth cycle and its production was maximum after 48 h of culture in tomato juice medium at an initial pH of 6.5. The bactericidal effect was observed.

Characterization of bacteriocin produced by Pediococcus pentosaceus from wine

The aim of this work was to investigate the antibacterial activity of flavonoid and nonflavonoid phenolic compound combinations and the synergistic antibacterial effects against Escherichia coli ATCC 35218. In nutrient medium, the combinations of gallic and protocatechuic acids, gallic and caffeic acids, and rutin and quercetin were the best antibacterial agents, with synergistic effects, and were selected to test their activity in a meat model system. All combinations diminished the bacterial growth, without cellular death at 20 degrees C. The combinations of gallic and caffeic acids and rutin and quercetin were the most effective at 4 degrees C; no viable cells were detected with 100 or 200 mg/L at 21 or 14 days of incubations, respectively. The lowest decimal reduction times were found with the rutin-quercetin combination. These results demonstrate a synergistic effect of the selected combination of flavonoid or nonflavonoid compounds with an important antibacterial effect in meat, using low concentrations.

Phenolic compound combinations on Escherichia coli viability in a meat system.

The synthesis of pectinesterase (PE) and polygalacturonase (PG) by a strain ofAspergillus niger isolated from rotten lemons was repressed by glucose, even in the presence of the inducer. The production of both enzymes started again once the sugar was used up, or when the mycelium was washed free of glucose and incubated in a glucose-free medium containing the inducer; this proved the reversibility of the repression mechanism. The effect of glucose was also tested in the absence of transcription. The results obtained suggest that repression occurs at the translational level.

Catabolite repression of the synthesis of inducible polygalacturonase and pectinesterase byAspergillus niger sp.

Lactobacillus rhamnosus ATCC 7469 was able to grow in glycerol as the sole source of energy in aerobic conditions, producing lactate, acetate, and diacetyl. A biphasic growth was ob

Glycerol metabolism of Lactobacillus rhamnosus ATCC 7469: cloning and expression of two glycerol kinase genes.

Glycerol catabolism was studied in Lactobacillus hilgardii X(1)B from wine, growing on glycerol and limiting glucose or fructose concentrations in anaerobiosis and microaerophilia. Glycerol consumption occurred simultaneously with sugar use, and it was higher with fructose as a cofermenting sugar in microaerophilia. Enzymatic activities of the glycerol kinase and glycerol dehydratase pathways were detected in both incubation conditions. In anaerobiosis, the main products were lactate, acetate, ethanol, and the intermediary product of the glycerol dehydratase pathway, 3-hydroxypropionaldehyde. However, in microaerophilia, 1,3-propanediol was also detected. In anaerobic glucose + glycerol and fructose + glycerol cultures as in microaerophilic glucose + glycerol cultures, glycerol was degraded mainly through the reductive pathway. However, when L. hilgardii X(1)B was grown on fructose + glycerol cultures in microaerophilia, glycerol dissimilation occurred mainly via the glycerol kinase way. According to these results, L. hilgardii X(1)B can degrade glycerol by producing 3-hydroxypropionaldehyde and acetic acid, both undesirable products for wine sensorial quality.

Ana M. Strasser de Saad

Papers

Characterization of bacteriocin produced by Pediococcus pentosaceus from wine

Phenolic compound combinations on Escherichia coli viability in a meat system.

Catabolite repression of the synthesis of inducible polygalacturonase and pectinesterase byAspergillus niger sp.

Glycerol metabolism of Lactobacillus rhamnosus ATCC 7469: cloning and expression of two glycerol kinase genes.

Sugar-glycerol cofermentations by Lactobacillus hilgardii isolated from wine.