Properties of the cellulolytic system from Aspergillus niveus

Lytic activity in pearl millet: its role in downy mildew disease resistance

Sclerospora graminicola causes downy mildew disease in susceptible pearl millet. Molecular basis of downy mildew disease resistance has been studied. Coleoptile region has been shown earlier to be the most susceptible site for attack by the pathogen. Lytic activity is differentially expressed in the coleoptile region of 3-day-old pearl millet seedlings of resistant and susceptible cultivars. Significantly higher levels of lytic factors were measured in the coleoptile region of resistant cultivars (100%) than in that of susceptible cultivars (20%). Both constitutive and inducible lytic factors were observed in different resistant cultivars, and they were able to lyse the pathogen. The level of lytic activity correlated well with the degree of resistance as evaluated by field screening studies. The present study, therefore, proposes that lytic factors found in the coleoptile region of the pearl millet seedling, are responsible for the lysis of the pathogen in the resistant plant, and may therefore provide resistance to downy mildew disease. This study also provides a simple method to evaluate downy mildew resistance in pearl millet cultivars.

Characterization of extracellular proteases from Trametes trogii

The peptidase activities excreted in culture broths of Trametes trogii mycelium have been identified by determining the digestion pathway of various peptides. Insulin beta-chain (30 residues), procasomorphin (10 residues) and two peptides of five residues (proctolin and thymosin alpha 1 fragment 23-27) were utilized as model substrates. Aminopeptidase, carboxypeptidase, endopeptidase and dipeptidyl aminopeptidase activities were revealed and information on their specificity was deduced. Preliminary data on the pH-dependent activity of the peptidases were also obtained by sequence analysis of the fragment mixtures produced at different pH values.

Submerged batch culture of the psychrophile Monographella nivalis in a defined medium; growth, carbohydrate utilization and responses to temperature

An asporogenous strain of the pink snow mould fungus, Monographella nivalis (Schaffnit) E. Müller, anamorph Gerlachia nivalis (Ces. ex Sac.) W. Gams & E. Müller (Syn. Fusarium nivale Ces. ex Sacc.), grew at 5 °C on a denned salts medium plus vitamins and utilized a variety of simple and polymeric carbohydrates as the sole carbon and energy source. Mycelium was grown at temperatures between 3 and 15 °C in aerated submerged fermentation culture in chemically defined medium plus sucrose. Optimum growth rates of 0·035-0·033 h^-1 occurred between 9 and 12 °C. Growth in a simple medium showed that all biochemical and physiological processes necessary for growth were functional at 3 °C. The growth performance of the organism at low temperatures was no better than would be expected from extrapolation of mesophilic growth responses to temperature. The optimum growth temperature of 9-12°C showed that some biochemical or physiological process was impaired above 12 °C. Uptake and incorporation of ³⁵ S-methionine by mycelium at different temperatures showed that general protein synthesis increased up to 25 °C, and hence was not responsible per se for the sensitivity to temperatures above 12 °C. Heat shock proteins were synthesized at the relatively low temperature of 25 °C, consistent with the low temperature optimum for growth. When grown with sucrose as the sole carbon source, the mycelium catalyzed the extracellular hydrolysis of sucrose, releasing glucose and fructose together with a small amount of fructan trisaccharides and a trace of tetra- and penta-saccharides. Fructan accumulation was transient, corresponding with maximal rates of sucrose hydrolysis. Most biomass formation occurred in the absence of fructan in the culture, hence fructan was not necessary for growth at low temperature and did not appear to function as a cryoprotectant. Invertase activity was mostly (60-70%) bound to mycelium; the remainder was free in the culture supernatant. The regulation of invertase expression appeared to be by sucrose-induction, rather than by end-product repression. Rates of sucrose hydrolysis in culture were temperature-sensitive and were markedly depressed above 12 °C, indicating inhibition of invertase formation.