A screening system for carbon sources enhancing beta-N-acetylglucosaminidase formation in Hypocrea atroviridis (Trichoderma atroviride).

To identify carbon sources that trigger beta-N-acetylglucosaminidase (NAGase) formation in Hypocrea atroviridis (anamorph Trichoderma atroviride), a screening system was designed that consists of a combination of Biolog Phenotype MicroArray plates, which contain 95 different carbon sources, and specific enzyme activity measurements using a chromogenic substrate. The results revealed growth-dependent kinetics of NAGase formation and it was shown that NAGase activities were enhanced on carbon sources sharing certain structural properties, especially on alpha-glucans (e.g. glycogen, dextrin and maltotriose) and oligosaccharides containing galactose. Enzyme activities were assessed in the wild-type and a H. atroviridis Deltanag1 strain to investigate the influence of the two NAGases, Nag1 and Nag2, on total NAGase activity. Reduction of NAGase levels in the Deltanag1 strain in comparison to the wild-type was strongly carbon-source and growth-phase dependent, indicating the distinct physiological roles of the two proteins. The transcript abundance of nag1 and nag2 was increased on carbon sources with elevated NAGase activity, indicating transcriptional regulation of these genes. The screening method for the identification of carbon sources that induce enzymes or a gene of interest, as presented in this paper, can be adapted for other purposes if appropriate enzyme or reporter assays are available.