Development of a low-cost cellulase production process usingTrichoderma reeseifor Brazilian biorefineries.
BACKGROUND
During the past few years, the first industrial-scale cellulosic ethanol plants have been inaugurated. Although the performance of the commercial cellulase enzymes used in this process has greatly improved over the past decade, cellulases still represent a very significant operational cost. Depending on the region, transport of cellulases from a central production facility to a biorefinery may significantly add to enzyme cost. The aim of the present study was to develop a simple, cost-efficient cellulase production process that could be employed locally at a Brazilian sugarcane biorefinery.


RESULTS
Our work focused on two main topics: growth medium formulation and strain improvement. We evaluated several Brazilian low-cost industrial residues for their potential in cellulase production. Among the solid residues evaluated, soybean hulls were found to display clearly the most desirable characteristics. We engineered aTrichoderma reeseistrain to secrete cellulase in the presence of repressing sugars, enabling the use of sugarcane molasses as an additional carbon source. In addition, we added a heterologous β-glucosidase to improve the performance of the produced enzymes in hydrolysis. Finally, the addition of an invertase gene fromAspegillus nigerinto our strain allowed it to consume sucrose from sugarcane molasses directly. Preliminary cost analysis showed that the overall process can provide for very low-cost enzyme with good hydrolysis performance on industrially pre-treated sugarcane straw.


CONCLUSIONS
In this study, we showed that with relatively few genetic modifications and the right growth medium it is possible to produce considerable amounts of well-performing cellulase at very low cost in Brazil usingT. reesei. With further enhancements and optimization, such a system could provide a viable alternative to delivered commercial cellulases.
VTT Brasil Ltda., Barueri, Sao Paulo Brazil.|VTT Technical Research Centre of Finland, Tietotie 2, 02044 Espoo, Finland.
Simo
0000-0001-7516-3363
S
Ellilä
VTT Brasil Ltda., Barueri, Sao Paulo Brazil.
Lucas
L
Fonseca
VTT Brasil Ltda., Barueri, Sao Paulo Brazil.
Cristiane
C
Uchima
VTT Brasil Ltda., Barueri, Sao Paulo Brazil.|Instituto de Ciências Agrárias, Universidade Federal de Minas Gerais (UFMG), Montes Claros, MG Brazil.
Junio
J
Cota
Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de Sao Paulo, Ribeirão Preto, SP Brazil.
Gustavo Henrique
GH
Goldman
VTT Technical Research Centre of Finland, Tietotie 2, 02044 Espoo, Finland.
Markku
M
Saloheimo
VTT Brasil Ltda., Barueri, Sao Paulo Brazil.
Vera
V
Sacon
VTT Technical Research Centre of Finland, Tietotie 2, 02044 Espoo, Finland.
Matti
M
Siika-Aho
Biorefinery; Brazil; Cellulase; Cellulosic ethanol; Enzyme; Molasses; On-site; Soybean hulls; Sugarcane; Trichoderma reesei