A. M. Strasser de Saad

Pediocin N5p from Pediococcus pentosaceus: adsorption on bacterial strains

Abstract Pediocin N5p is a bacteriocin produced by Pediococcus pentosaceus isolated from wine. It is adsorbed on both sensitive and resistant Gram-positive and Gram-negative bacteria in non specific (non lethal) sites and higher values, up to 30% are observed in sensitive strains suggesting the presence of particular (lethal) receptors. Cell death without lysis is produced by the action of pediocin on sensitive strains. The cations Mg 2 + and Mn 2 + increase the pediocin binding by 80 and 100%, respectively. Treatment of sensitive cells with proteolytic enzymes and 1% SDS increases the subsequent binding of bacteriocin by 100 and 25%, respectively. As a lipid moiety of pediocin N5p is critical to its activity, probably a hydrophobic interaction with the peptidic receptor, stabilized by Mn 2 + or Mg 2 + might be established. Pediocin N5p adsorption is not affected by ethanol and SO 2 , two factors involved in vinification.

Exoprotease activity of Leuconostoc oenos in stress conditions

Exoprotease activity during 48 h of total energy and nutrient starvation was examined in Leuconostoc oenos X2L isolated from wine. Starved cells after 2 h of incubation at 30 °C in citrate buffer, 0.05 mmol 1−1 pH 5, showed greater extracellular proteolytic activity than at the onset of starvation. In the presence of 60 mg l−1 SO2 and 8% or 12% ethanol, the proteolytic activity was higher ; 10 mmol l−1 Ca2+ and Mg2+ produced an increase in protease activity during starvation. Glucose and 2‐deoxyglucose (2‐DOG) were found to repress synthesis by 80% and 100%, respectively. Cyclic adenosine 3′‐5′‐phosphate increased the exoprotease activity and reverted the repression by glucose and 2‐DOG. De novo synthesis of proteins was required for the exoprotease activity by cells submitted to stress conditions. The absence of protease activity in the supernatant fluids from chloramphenicol‐treated cells indicated that the activity is a result of deliberate release and not of passive cell lysis.

Methanol utilization by a strain of Aspergillus niger: influence on the synthesis and activity of pectinases

During the production of pectinases by a strain of Aspergillus niger isolated from rotten lemons, methanol was liberated into the medium due to the cleavage of the pectin molecule used as the carbon source. The methanol was subsequently consumed by the microorganism but neither the synthesis nor the activity of pectinesterase and polygalacturonase was affected. Although not studied in detail, the mechanism involved in the utilization of methanol is similar to that described for methylotrophic yeasts.

Sugar and malic acid utilization and acetic acid formation byLeuconostoc oenos.

Leuconostoc oenos ST8, isolated from an Argentinian red wine, utilized glucose, fructose and malic acid and produced acetic acid. Fructose was preferred to glucose as a source of carbohydrate. Malic acid was almost completely degraded in 3 days at 25°C. Acetic acid formation correlated with fructose utilization.Leuconostoc oenos ST8, isolated from an Argentinian red wine, utilized glucose, fructose and malic acid and produced acetic acid. Fructose was preferred to glucose as a source of carbohydrate. Malic acid was almost completely degraded in 3 days at 25°C. Acetic acid formation correlated with fructose utilization.

Effect of physicochemical factors on glycerol production by simultaneous cultures of wine micro-organisms using the response surface method

To evaluate the effect of temperature, pH and SO2 on growth and glycerol production improvement by Saccharomyces cerevisiae mc2, Kloeckera apiculata mF and Oenococcus oeni X2L using the response surface method (RSM).