Role of phospholipase C and protein kinase C in Aspergillus nidulans during growth on pectin or glucose: Effects on germination and duplication cycle.

The effects of PLC and Pkc inhibitors on Aspergillus nidulans depend on the carbon source. PLC inhibitors Spm and C48/80 delayed the first nuclear division in cultures growing on glucose, but stimulated it in media supplemented with pectin. Less intense were these effects on the mutant transformed with PLC-A gene rupture (AP27). Neomycin also delayed the germination in cultures growing on glucose or pectin; however, on glucose, the nuclear division was inhibited whereas in pectin it was stimulated. These effects were minor in AP27. The effects of Ro-31-8425 and BIM (both Pkc inhibitors) were also opposite for cultures growing on glucose or pectin. On glucose cultures of both strains BIM delayed germination and the first nuclear division, whereas on pectin both parameters were stimulated. Opposite effects were also detected when the cultures were growing on glucose or pectin in the presence of Ro-31-8425.

Sequential synthesis and secretion of pectinases by Penicillium frequentans.

Penicillium frequentans synthesized eleven polygalacturonases and three pectinesterases when grown in the presence of pectin, sodium polypectate or monogalacturonic acid. When glucose was the sole carbohydrate source in the medium two of these polygalacturonases and one pectinesterase were produced. The enzymes produced under any of these conditions degraded pectic substrates to monogalacturonic acid, suggesting that this monosaccharide or its metabolites should induce the pectinolytic complex. All pectinesterases and most of the extracellular polygalacturonases were synthesized after the 2nd hour of incubation. The pectinases produced by Penicillium frequentans were not secreted at the same time but after 5 hours of incubation all of them could be detected outside the cell those detected only inside the cell were probably membrane-associated or unglycosylated forms of the extracellular pectinases.

Studies of pectic enzymes produced by Talaromyces flavus in submerged and solid substrate cultures.

Tons of peel and rag are generated each year by industries of citrus fruit juices. These by-products are used either for the elaboration of pectin or as substrate for enzyme production. Talaromyces flavus produces extracellular pectinesterase and polygalacturonase after 24 h in submerged culture supplemented with 0.5-0.8% citrus pectin preceded by preculture for 24 h in 2% (w/v) sucrose or in solid substrate culture on passion fruit peel, lemon or orange pulp pellets after 3-6 days of incubation. Chromatographic profiles in a CM-Sepharose column of liquid and solid cultures were very similar, consisting of one endopoligalacturonase (endo-PG I) and one pectinolytic complex constituted by an endopoligalacturonase (endo-PG II) and pectinesterase. Pectin and pectate lyases were undetectable in both media. In Talaromyces flavus the synthesis of pectinases was repressed by glucose and finally controlled by the concentration of products from pectic enzymes degradation.

Comparative study of intracellular and extracellular pectinases produced by Penicillium frequentans.

The filamentous fungus Penicillium frequentans synthesized eleven polygalacturonases (PGs) and two pectinesterases (PEs) when grown in liquid culture supplemented with pectin. Seven PGs and the two PEs were secreted in the medium, whereas four PGs were not secreted. Among the secreted PGs, the endo-PG (band 10) and exo-PGs (band 5) were the enzymes secreted at the highest levels. All secreted PGs bound to lectin and their secretion and/or enzymic activities were inhibited by tunicamycin (TM), except for the constitutive and inducible endo-PG (band 10). Studies on the affinity for concanavalin A (ConA) and the effect of TM suggested that the secreted endo-PG and exo-PG differed in level and process of glycosylation. The exo-PG was characterized as a N-glycoprotein, whereas the endo-PG is probably an O-glycoprotein. The PGs (bands 3 and 4) were neither bound to ConA nor secreted and their enzymic activities were inhibited by TM, suggesting that they are probably N-glycoproteins with complex oligosaccharides of type three and tetra-antennary structure. The other PGs (bands 6 and 8) that were not secreted and did not bind to ConA were not inhibited by TM. These enzymes presented chromatographic characteristics and effects with TM that were similar to endo-PG (band 10), because these PGs might be unglycosylated or/and aggregate forms of the endo-PG (band 10).