avoided the production of many enzymes and microbial products. Solving these
problems may prove difficult as many of the said problems are responsible for the
advantages, for example, formation of gradients is given as the cause for heterogeneity along the culture which has been pointed as responsible for higher enzyme
production, and the low content of water that promotes heat build up keeps
enzymes from being diluted. Working in the engineering aspects and the scale-up
will require further research on bioreactor design and operation (Lonsane et al.
1992).
7.6 Improving Systems
7.6.1 Co-Cultivation
The conversion of lignocellulosic material in precursor products requires the synergic action of different enzymes and all the known microbial species show deficiencies in some or several of the enzymatic activities required to degrade this
material, for example, as discussed previously, A. niger is a good degrader of pectic
materials, while Trichoderma reesei is a good producer of cellulose degrading
enzymes. This has given rise to the idea of a co-cultivation of both organisms for the
production of lignocellulose degradation enzymes used in the treatment of cellulose
waste (Maheshwari et al. 1994). Kumar and Singh (2001) reported the co-cultivation of Aspergillus niger and Trichoderma reesei for the degradation of aquatic
weed. In that work, they reported an increase of 20–24 % in endo and exoglucanase
activities and about a 13 % increase in the beta-glycosidase activity compared to
the maximum enzymatic activities under single culture conditions.
7.6.2 Mutagenesis
It is known that production of biomass degrading enzymes is controlled by
induction, catabolite repression, and end-product inhibition, so it is normal that at
the beginning, search for hyper-producing lignocellulose degrading organisms was
attempted by random mutagenesis looking for improvements in cellulase production and mutants insensible to catabolite repression. Successful cases of higher
productivity of cellulases producing organisms obtained by mutagenesis are quite
rare, a 4x higher production of cellulose was obtained by mutagenesis of a Bacillus
strain free of catabolite repression (Kotchoni et al. 2003). While Kuhad et al.
(1994) reported a Fusarium oxysporum cellulose hyperproducer mutant obtained
by UV treatment followed by chemical mutagenesis with nitrosoguanidine showed
an increase of 80 % in cellulose production (Kuhad et al. 1994), many Trichoderma reesei mutants used for commercial production of cellulose are derived
242
S. de J. Romero-Gómez
problems may prove difficult as many of the said problems are responsible for the
advantages, for example, formation of gradients is given as the cause for heterogeneity along the culture which has been pointed as responsible for higher enzyme
production, and the low content of water that promotes heat build up keeps
enzymes from being diluted. Working in the engineering aspects and the scale-up
will require further research on bioreactor design and operation (Lonsane et al.
1992).
7.6 Improving Systems
7.6.1 Co-Cultivation
The conversion of lignocellulosic material in precursor products requires the synergic action of different enzymes and all the known microbial species show deficiencies in some or several of the enzymatic activities required to degrade this
material, for example, as discussed previously, A. niger is a good degrader of pectic
materials, while Trichoderma reesei is a good producer of cellulose degrading
enzymes. This has given rise to the idea of a co-cultivation of both organisms for the
production of lignocellulose degradation enzymes used in the treatment of cellulose
waste (Maheshwari et al. 1994). Kumar and Singh (2001) reported the co-cultivation of Aspergillus niger and Trichoderma reesei for the degradation of aquatic
weed. In that work, they reported an increase of 20–24 % in endo and exoglucanase
activities and about a 13 % increase in the beta-glycosidase activity compared to
the maximum enzymatic activities under single culture conditions.
7.6.2 Mutagenesis
It is known that production of biomass degrading enzymes is controlled by
induction, catabolite repression, and end-product inhibition, so it is normal that at
the beginning, search for hyper-producing lignocellulose degrading organisms was
attempted by random mutagenesis looking for improvements in cellulase production and mutants insensible to catabolite repression. Successful cases of higher
productivity of cellulases producing organisms obtained by mutagenesis are quite
rare, a 4x higher production of cellulose was obtained by mutagenesis of a Bacillus
strain free of catabolite repression (Kotchoni et al. 2003). While Kuhad et al.
(1994) reported a Fusarium oxysporum cellulose hyperproducer mutant obtained
by UV treatment followed by chemical mutagenesis with nitrosoguanidine showed
an increase of 80 % in cellulose production (Kuhad et al. 1994), many Trichoderma reesei mutants used for commercial production of cellulose are derived
242
S. de J. Romero-Gómez