ABSTRACT

Two fungi, Aspergillus niger and Fusarium cuimorum, isolated from soil showed strong cellulase activity on carboxymethyl cellulose agar. Both fungi were subsequently studied for cellulase production potential on lignocellulosics such as corn cob, elephant grass, rice husk and saw dust using submerged and solid state fermentation techniques. Pretreated lignocellulosics using a combined alkali and steam pretreatments gave better cellulase and sugar yields. Maximum levels of cellulase occurred at 24-72 h although activities were observed for 96-120 h. Production of cellulase was better (0.598 ± 0.002Uml') in corn cob while saw dust had the least activity (0.102 + 0.00 1Uml') with respect to A. niger. A similar trend was observed with F. culmorum. Aspergillus niger cultures grown in corn cob yielded highest reducing sugar (1.3 54 ± 0.001 .iMolemL') while in Fusarium cultures, the highest amount of reducing sugar was released also from corn cob (0.991 ± 0.002jiMoleml'). Optimum conditions for growth and enzyme production were pH 7 at 30 °C for A. niger In contrast, optimum conditions for both growth and enzyme production for F culmorum was at pH 6 at 25°C. The influence of supplemental carbon and nitrogen sources was examined in connection with growth and enzyme production. Enhanced lignocelluloses degradation was obtained with maltose and groundnut meal as supplemental carbon and nitrogen sources. Groundnut meal at lg/looml concentration stimulated higher enzyme secretion than inorganic nitrogen compounds. Lignocellulose degradation was optimized by culture agitation at 150 rpm. Partially purified cellulase preparations showed temperature and pH dependence for the two organisms and saccharified both pure and crude cellulose substrates. . The proximate compositions of the microbial degraded lignocellulose samples evaluated indicated the presence of low quantities of nitrogen. Paper chromatographic analysis of the products of hydrolysis of the cellulosic substrates showed that glucose was the main product. Thus, the effective bioconversion of lignocellulose wastes can be important means to produce sugar and chemical feedstock as well as an environmental waste management option.