Effect of glucose level on the batch production of β-1,3-glucanase by Trichoderma harzianum and cell growth

Abstract

The effect of initial glucose concentration on b-1, 3-glucanase production by Trichoderma harzianum NCIM 1185 and cell growth was studied in a batch stirred tank bioreactor. The initial glucose level was varied between 5 g/dm 3 and 100 g/dm 3 . A maximum b-1,3-glucanase production of 0.820 U was obtained using the fully optimized medium which had an initial glucose level of 8.63 g/dm 3 and thereafter there was a steady decrease in b-1,3-glucanase production. No b-1,3-glucanase production was observed beyond initial glucose concentrations of 40 g/dm 3 which suggests a possible catabolic repression on the enzyme synthesis. The inhibitory effect of increased initial glucose concentrations on cell growth has been studied and the Luong and the Han-Levenspiel models were used to explain the mechanism of inhibition. List of symbolsC A Substrate concentration in the Han-Levenspiel model (g/dm 3 ) C Ã A Critical substrate concentration above which growth stops (The Han-Levenspiel model) (g/dm 3 ) C c Cell concentration in the Han-Levenspiel model (g/ dm 3 ) C M Monod's constant (The Han-Levenspiel model) (g/ dm 3 ) K S Saturation constant (g/dm 3 ) m Constant in the Han-Levenspiel model (dimensionless) n Constant in the Luong and the Han-Levenspiel models (dimensionless) r c Growth rate of cells (g/(dm 3 )(h)) S Substrate concentration (Luong's model) (g/dm 3 ) t time (h) l Speci®c growth rate (h À1 ) l m Maximum speci®c growth rate (h À1 ) l obs Observed speci®c growth rate (h À1 ) 1 Introduction b-1,3-glucanase (b-1,3-glucan 3-glucanohydrolase, E.C.3.2.1.6) is an important lytic enzyme which has been used as biocontrol agent against plant-pathogenic fungi [1], for the elucidation of fungal cell wall structure and b-1,3-glucan structure [2], and for discerning taxomonic and evolutionary relationships among yeasts [3]. This enzyme also ®nds application in the brewing industry [4] and in the preparation of protoplasts [5]. The enzyme is also implicated in fungal cell lysis [6], parasitism of fungi by other fungi [7], seed germination [8], and various yeast life cycle processes requiring cell wall hydrolysis [9].Our earlier communication elsewhere [10] dealt with the optimization of the medium constituents for maximum b-1,3-glucanase production by Trichoderma harzianum employing response surface methodology. In the present study, the effect of initial glucose concentration and b-1,3-glucanase production by Trichoderma harzianum NCIM 1185 and cell growth were investigated in a batch stirred tank bioreactor. Materials and methods Organism and culture maintenanceTrichoderma harzianum NCIM 1185 was obtained from the National Chemical Laboratory, Pune, India. The organism was maintained on potato-dextrose-agar slants, subcultured every 3 months and stored at 4 AE 1 C. Medium and culture conditionsThe medium recommended by The Âodore and Panda [10] for b-1,3-glucanase production by T. harzianum was employed. 100 cm 3 medium in a 500-cm 3 Erlenmeyer¯ask was inoculated with 5% (v/v) of conidial suspension (approximately 10 6 conidi...