Biomedical subjects

G Viniegra-González

Publications and source records attributed to G Viniegra-González.

6 recordsLinked to original sources

PubMed2004

Denitrification in presence of benzene, toluene, and m-xylene: kinetics, mass balance, and yields.

Denitrification of the electron donors toluene-C (15-100 mg/L), m-xylene-C (15-70 mg/L), benzene-C (5-25 mg/L), and acetate-C as experimental reference (50-140 mg/L) was carried out in batch culture. An initial concentration of 1.1 +/- 0.15 g of volatile suspended solids/L of denitrifying sludge without previous exposure to aromatic compounds was used as inoculum. The results showed toluene and nitrate consumption efficiency (ET and EN, respectively) of 100%. Toluene was completely mineralized (oxidized) to CO2. In all cases, the N2 (YN2) and HCO3-yields (YHCO3) were 0.97 +/- 0.01 and 0.8 +/- 0.05, respectively. The consumption efficiency (EX) of m-xylene (53 +/- 5.7%) was partial. The YN2 and YHCO3 were 0.96 +/- 0.01 and 0.86 +/- 0.02, respectively. Benzene was not consumed under denitrifying conditions. The specific consumption rates of toluene (qT) and m-xylene (qX) were lower than that of acetate (qA). The differences in specific consumption rates were probably owing to the negative effect of benzene, toluene, and isomers of xylene on the cell membrane.

Acetates↗

PubMed2001

Exopectinases produced by Aspergillus niger in solid-state and submerged fermentation: a comparative study.

Exopectinase production by Aspergillus niger was compared in submerged fermentation (SmF) and solid-state fermentation (SSF). SSF was carried out using polyurethane foam (PUF) as the solid support. The purpose was to study the effect of sucrose addition (0 or 40 g/l) and water activity level (A(w)=0.99 or 0.96) on the level of enzyme activity induced by 15 g/l of pectin. Mycelial growth, as well as extracellular protease production, was also monitored. Sucrose addition in SmF resulted in catabolite repression of exopectinase activity. However, in SSF, an enhancement of enzyme activity was observed. Protease levels were minimal in SSF experiments with sucrose and maximal in SmF without sucrose. Exopectinase yields (IU/g X) were negligible in SmF with sucrose. The high levels of exopectinase with sucrose and high A(w) in SSF can be explained by a much higher level of biomass production without catabolite repression and with lower protease contamination.

Aspergillus niger↗

PubMed2001

Production of tannase by Aspergillus niger Aa-20 in submerged and solid-state fermentation: influence of glucose and tannic acid.

Tannase production by Aspergillus niger Aa-20 was studied in submerged (SmF) and solid-state (SSF) fermentation systems with different tannic acid and glucose concentrations. Tannase activity and productivity were at least 2.5 times higher in SSF than in SmF. Addition of high tannic acid concentrations increased total tannase activity in SSF, while in SmF it was decreased. In SmF, total tannase activity increased from 0.57 to 1.03 IU/mL, when the initial glucose concentration increased from 6.25 to 25 g/L, but a strong catabolite repression of tannase synthesis was observed in SmF when an initial glucose concentration of 50 g/L was used. In SSF, maximal values of total tannase activity decreased from 7.79 to 2.51 IU when the initial glucose concentration was increased from 6.25 to 200 g/L. Kinetic results on tannase production indicate that low tannase activity titers in SmF could be associated to an enzyme degradation process which is not present in SSF. Tannase titers produced by A. niger Aa-20 are fermentation system-dependent, favoring SSF over SmF.

Aspergillus niger↗

PubMed1998

Overproduction of rifamycin B by Amycolatopsis mediterranei and its relationship with the toxic effect of barbital on growth.

A novel method for selecting overproducing strains of rifamycin B was developed. This technique involves the use of lysozyme and the effect of barbital on the growth of A. mediterranei. Complete medium added with glycine and barbital was inoculated with mutagenized mycelium, incubated for 48 hours and treated with lysozyme. The lysozyme resistant mycelium was washed with dilute detergent. Complete medium with glycine but without barbital was inoculated with the washed mycelium. Protoplasts were obtained and regenerated and the colonies were picked and seeded on Bennet agar plates with and without barbital. Two selected mutants were sensitive to 0.5% barbital producing 200% more rifamycin than the parental strain. In addition, 30 barbital resistant mutants were isolated and their production level was lower than the one observed with the parental strain. These results suggest that the effect of barbital on secondary metabolism (rifamycin production) is related to its effect on primary metabolism.

Actinobacteria↗

PubMed1995

Production and properties of three pectinolytic activities produced by Aspergillus niger in submerged and solid-state fermentation.

Three extracellular pectinases were produced by Aspergillus niger CH4 by submerged and solid-state fermentation, and their physicochemical and kinetic properties were studied. The highest productivities of endo- and exo-pectinase and pectin lyase were obtained with solid-state fermentation. The kinetic and physicochemical properties of these enzymes were influenced by the type of culture method used. All activities were very different in terms of pH and temperature optima, stability at different pH and temperature values and affinity for the substrate (Km values). In solid-state fermentation, all pectinase activities were more stable at extreme pH and temperature values but the Km values of endo-pectinase and pectin lyase were higher with respect to those activities obtained by the submerged-culture technique. The pectin lyase activity obtained by the submerged-culture technique showed substrate inhibition but the enzyme obtained by solid-state fermentation did not. Electrophoresis, using sodium dodecyl sulphate/polyacrylamide gel with enzymatic extracts obtained for both culture methods, showed the same number of protein bands but some differences were found in their electrophoretic position. The results obtained in this work suggest that the culture method (submerged or solid-state) may be responsible for inducing changes in some of the pectinolytic enzymes produced by A. niger.

Aspergillus niger↗

PubMed1993

New approach for selecting pectinase producing mutants of Aspergillus niger well adapted to solid state fermentation.

The aim of this paper is to review and study a new approach for improving strains of Aspergillus niger specially adapted to produce pectinases by Solid State Fermentation (SSF) with materials having low levels of water activity (a(w)), i.e., coffee pulp. Special emphasis is placed on the use of two antimetabolic compounds: 2-deoxy-glucose (DG) and 2,4-dinitro-phenol (DNP) combined with a water depressant (ethylene glycol = EG) in order to put strong selection pressures on UV treated spores from parental strain C28B25 isolated from a coffee plantation. Such a strain was found to be DG sensitive. Results suggested the existence of a reciprocal relation between adaptation of isolated strains to SSF or to Submerged Fermentation (SmF) systems. Preliminary physiological analysis of isolated strains showed that at least some few initially DG resistant mutants could revert to DG sensitive phenotype but conserving increased pectinase production. Also it was found that phenotype for DNP resistance could be associated to changes of DG resistance. Finally, it was found that low levels of a(w) produced by adding 15% EG to agar plates, were a significant selection factor for strains well adapted to SSF system.

Journal Article↗