Scale up and efficient bioethanol production involving recombinant cellulase (Glycoside hydrolase family 5) from Clostridium thermocellum

Abstract

Background: Lignocellulose degrading fungal enzymes have been in use at industrial level for more than three decades. However, the main drawback is the high cost of the com. available Trichoderma reesei cellulolytic enzymes. Results: The hydrolytic performance of a novel Clostridium thermocellum cellulolytic recombinant cellulase expressed in Escherichia coli cells was compared with the naturally isolated cellulases in different modes of fermn. trials using steam explosion pretreated thatch grass and Zymomonas mobilis. Fourier transform IR (FT-IR) spectroscopic anal. confirmed the efficiency of steam explosion pretreatment in significant release of free glucose moiety from complex lignocellulosic thatch grass. The recombinant GH5 cellulase with 1% (w v-1) substrate and Z. mobilis in shake flask sep. hydrolysis and fermn. (SHF) and simultaneous saccharification and fermn. (SSF) trials demonstrated highest ethanol titer (0.99 g L-1, 1.2 g L-1) as compared to Bacillus subtilis (0.51 g L-1, 0.72 g L-1) and Trichoderma reesei (0.67 g L-1, 0.94 g L-1). A 5% (w v-1) substrate with recombinant enzyme in shake flask SSF resulted in a 7 fold increment of ethanol titer (8.8 g L-1). The subsequent scale up in a 2 L bioreactor with 1 L working vol. yielded 16.13 g L-1 ethanol titer implying a 2 fold upturn. The rotary evaporator based product recovery from bioreactor contributed 94.4 (%, v v-1) pure ethanol with purifn. process efficiency of 22.2%. Conclusions: The saccharification of steam exploded thatch grass (Hyparrhenia rufa) by recombinant cellulase (GH5) along with Z. mobilis in bioethanol prodn. was studied for the first time. The effective pretreatment released substantial hexose sugars from cellulose as confirmed by FT-IR studies. In contrast to two modes of fermn., SSF processes utilizing recombinant C. thermocellum enzymes have the capability of yielding a value-added product, bioethanol with the curtailment of the prodn. costs in industry. [on SciFinder(R)]