Carlos Huitrón

Constitutive exo-pectinase produced by Aspergillus sp. CH-Y-1043 on different carbon source.

SummaryThe production of a constitutive exo-pectinase byAspergillus sp. CH-Y-1043 grown on glucose, sucrose, fructose, glycerol and galacturonic acid is reported. The specific activity was found to be in the range of 26% to 75% of that produced with pectin or poly-galacturonic acid. The production of this exo-pectinase is strictly correlated to the exponential growth phase and it is highly sensitive to the pH of the culture medium

Stimulation of the production of extracellular pectinolytic activities of Aspergillus sp. by galacturonic acid and glucose addition

Abstract We studied the effect of the addition of galacturonic acid and of glucose on the production of the pectinolytic activities by Aspergillus sp. The results showed that a differential response in the production of the activities was produced. The production of the pectinolytic activity as measured by reducing groups was not negatively affected when low concentrations of eithr glucose or galacturonic acid were added to growing pectin containing cultures of Aspergillus sp. regardless of the time of addition. The production of the activity, measured by viscosimetry, was stimulated by addition of galacturonic acid at 24 h, suggesting that galacturonic acid participates in the induction of pectinolytic activities of Aspergillus sp. When the addition was made at t = 0, the increase in pH seems to affect the production of this activity. The addition of glucose at 24 h had no effect on the production of the viscosimetric activity; however, catabolic repression was observed upon the addition at t = 0. The production of both pectinolytic activities was strongly repressed when glucose was added at high concentration and was affected less when galacturonic acid was added at the same high concentration.

Application of fed-batch cultures in the production of extracellular pectinases by Aspergillus sp.

Abstract The production of extracellular pectinases by Aspergillus sp. in fed-batch cultures was studied in a fermenter with recirculation of medium. The continuous recirculation of medium resulted in a 40 and 60% increase in the extracellular pectinolytic activity as measured by reducing groups and viscometry, respectively, compared to the non-recirculated culture. The effect of dilution of the medium by addition of nutrients was evaluated. The results showed that the production of these activities was not affected with respect to the non-diluted culture. When nitrogen, pectin or both were added in limiting concentrations, we found that activities determined by reducing groups were 36, 249 and 455%, respectively, compared to the non-limited culture. The values for the pectinolytic activities measured by viscometry were only 5, 32 and 100%, respectively .

β‐Xylosidase and xylanase characterization and production by Streptomyces sp. CH‐M‐1035

Extracellular xylanase activity and cell‐bound β‐xylosidase production by a selected strain of Streptomyces sp. CH‐M‐1035 was characterized during growth on three xylans, sugar cane bagasse pith and lemon peel as sole carbon source. The cell‐bound β‐xylosidase and extracellular endoxylanase had pH optima of 6·0 and 5·0, and temperature optima of 50°C and 60°C, respectively. The highest level of β‐xylosidase activity was obtained when Streptomyces sp. CH‐M‐1035 was grown on larchwood xylan, whereas the maximal endoxylanase production was found on lemon peel. Reducing sugars accumulated in the culture media when Streptomyces sp. CH‐M‐1035 was grown on xylans, but not on agroindustrial residues.

Pectin lyase from Aspergillus sp. CH-Y-1043

Aspergillus sp. CH-Y-1043 synthesizes pectin lyase when grown on citrus pectin at 37° C. Production is favoured by increased esterification degree of the pectin used as carbon source. This enzyme displays higher activity at pH values of 8.5–8.8 and temperatures of 40–45° C. The optimal substrate for the enzyme was highly esterified pectin and no enzymatic activity was registered on polygalacturonic acid. The activity is stimulated by, though not dependent on, divalent cations (Ca2+, Mg2+, Mn2+, Ba2+ and Co2+) and inhibited by Zn2+, and it is not sensitive to the addition of EDTA. The enzyme is very stable when exposed to pH variations: at 4° C it preserves more than 95% of its activity at pHs ranging from 2.0 to 10.0, and at 30° C stability is preserved at pHs ranging from 4.0 to 8.0. At a constant pH of 5.0, the enzyme conserves its stability at temperatures ranging from 4 to 50° C and at pH 8.0 sensitivity to temperature increased. The results on the endo-exo nature of the enzyme suggest that this is an exo-pectin lyase.

Endo-polygalacturonase production from untreated lemon peel byAspergillus sp. CH-Y-1043

SummaryEndo-polygalacturonase (endo-PG) production byAspergillus sp. CH-Y-1043 using untreated lemon peel as the sole carbon source was investigated. This strain was observed to produce more activity of endo-PG at 37°C than at 29°C. Untreated lemon peel proved to be a beeter substrate than citrus pectin for endo-PG production. Modification of the culture medium and lowering of the initial pH to 2.8 caused a 10-fold increase in the production of endo-PG activity using lemon peel.

Physiological studies on induction and catabolite repression of β-xylosidase and endoxylanase in Streptomyces sp. CH-M-1035

Abstract The specificity of induction of β-xylosidase and endoxylanase from Streptomyces sp. CH-M-1035 was investigated using mono-, di- and poly-saccharides, among other compounds. This microorganism was able to grow on all carbon sources except cellulose microcrystalline and methyl-β- D -xylopyranoside. β-Xylosidase was induced by larchwood xylan, birchwood xylan, oat spelts xylan and D -xylose. Basal levels of activity were obtained in sucrose, lactose, maltose and pectin. Endoxylanase activity was induced in presence of xylans, D -xylose, sucrose and D -arabinose. Both enzymes, β-xylosidase and endoxylanase, were repressed by the addition of glucose, glycerol and succinic acid to the culture medium containing 1% birchwood xylan. On the other hand, addition of methyl-β- D -xylopyranoside in the same conditions induced β-xylosidase but not endoxylanase synthesis. An unexpected stimulatory effect was observed on β-xylosidase biosynthesis when pyruvic acid was added to the culture medium independently of the xylan used.

Isolation of endopolygalacturonase hyperproducing mutants ofAspergillus sp. CH-Y-1043

SummaryWith the aim of obtaining hyperproducing strains of pectinases,Aspergillus sp. CH-Y-1043 was mutated with NTG and mutants resistant to glycerol catabolic repression were selected. Among the mutants obtained, CH-SS/ M63 produced an endo-PG activity 400% higher than the wild type, using lemon peel as the sole carbon source.

Glucose and glycerol repression of α-amylase in Streptomyces kanamyceticus and isolation of deregulated mutants

SummaryGlucose and glycerol at concentrations of 2 % negatively affected amylase synthesis in plate and submerged Streptomyces kanamyceticus cultures. This microorganism was insensitive to growth inhibition by glucose analogs and deregulated mutants were identified by a clearing zone around colonies grown on starch and glycerol or glucose, and selected. Three kinds of mutants were obtained: one insensitive to glucose (Mutant 41), another insensitive to glycerol repression (Mutant E) and the last (Mutant 29) an amylase-hyperproducing mutant, albeit regulated by glucose or glycerol like the wild type. The levels of glucokinase, an enzyme involved in catabolite regulation of Enterobacteria, were determined and results showed no differences between the parental strain and the mutants.

Protoplasts from pectinolytic fungi: isolation, regeneration and pectinolytic enzyme production

S. Solís, M.E. FLORES AND C. HUITRON. 1996. Protoplast release in pectinolytic strain mutants of Aspergillus sp. CH‐Y‐1043 (A13) and Aspergillus flavipes ATCC‐16795 (F7) is described. Optimum yield of protoplasts A13 was obtained in a lapse of 1 h when commercially lytic enzymes of Trichoderma harzanium (2 mg ml−1) were added in 0.05 mol 1−1 citrate‐phosphate buffer pH 5.0 containing 0.7 mol 1−1 KCl and 10 mg ml−1 BSA. Best results in F7 were obtained when the protoplasting system of A13 was supplemented with 10 mg ml−1Aureobasidium sp. lytic enzymes. Isolated protoplasts in A13 and F7 were capable of a high regeneration frequency of 87% and 53% when 0.7 mol 1−1 KCl and sorbitol were used as osmotic stabilizers. Endo‐P, Exo‐P and pectin lyase production were not modified during the process of regeneration.