Production of cell wall‐degrading enzymes by three isolates of Aspergillus niger under different cultivation conditions

Abstract

Three strongly pathogenic isolates of Aspergillus niger were capable of producing pectolytic, cellulolytic and proteolytic enzyme activities in various culture media, extracellularly, indicating the positive correlation between in vitro enzyme production and virulence of the pathogens.Cell wall-degrading enzymes play an important role during pathogenesis (ALBERSHEIM et al. 1969, MEHTA et al. 1974. Production of individual enzymes by the pathogens in a culture medium and the amount of activity in a crude enzyme extract are influenced by components of the culture media (MEHTA and MEHTA 1985). Certain substances present in the medium induce the secretion of enzymes (AYERS and PAPAVIZAS 1965), while other substances inhibit the secretion of enzymes (PATIL and DIMOND 1968). Many workers RICH 1958, VANCE et al. 1980) observed the production of cell wall-degrading enzymes in different culture media. Both, natural MEHTA 1985, MISHRA 1978) and synthetic media MEHTA 1985, HUSAIN andDIMOND 1958) have been widely used for the production of pectolytic and cellulolytic enzymes. REDDY et al. (1980) studied the effect of five synthetic media on the production of protease enzyme by Aspergillus niger. Production of cell wall-degrading enzymes in the diseased fruits infected with these isolates and also in culture provided the reason for studying the characteristics of these cell wall-degrading enzymes in detail. Therefore, it was thought desirable to determine the optimum cultural conditions for the production of these enzymes in vitro. Materials and methodsThree pathogenic forms of Aspergillus niger VAN TIECH were isolated from diseased Emblica officinalis GAERTN (isolate Al), Prunus dornestica L. (isolate A2) and Citrus rnedica L. (isolate A3) fruits by following routine mycological techniques. These isolates were found to cause severe fruit rot diseases both in field and in storage conditions. The isolates were maintained on CZAPEK'S agar slants. The pathogens were grown in ERLENMEYER flasks (150 ml) containing 25 ml of various broth media (Table 1) sterilized at 15 Ib pressure for 15 min. The inoculum consisted of a single disc (diam 8 mm) cut out from the margin of freshly grown colony (5 days) of the pathogens on CZAPEK'S agar medium. The inoculated flasks were incubated at 28 f 1 "C for 3, 6 , 9 and 12 d under stationary conditions. To determine the biomass the mycelial mat was harvested on preweighed WHATMAN filter paper No. I and dried to constant weight at 70 "C. The culture filtrates were directly centrifuged at 5,000 rpm for 20 min at 4 "C. The supernatant thus obtained was used as enzyme extract.Enzyme assay: OSWALD'S viscometers were clamped and fixed in a water bath (30 "C). The reaction mixture contained the following components (ml): For polygaiacturonase (PG): I .2% sodium polypectate (substrate) 3.5, distilled water 1.5, MCILVAIN'S buffer (pH 4.5) 1.5 enzyme extract 1.5. For pectinmethylgalacturonase (PMG): This enzyme was detected by using citrus pectin (1.2%) as substrate, while all other components bei...

Production of Pecticlyases by Three Thermophilic Fungi

“…Medium C which contained pectin supported maximum exo-PL suggesting the adaptive nature of the exo-PL of all the three thermophilic fungi under study. Similarly Mehta et al, (1993) have reported the adaptive nature of PL produced by Aspergillus niger.…”