Simultaneous and enhanced production of thermostable amylases and ethanol from starch by cocultures of Clostridium thermosulfurogenes and Clostridium thermohydrosulfuricum

Abstract

Clostridium thermosulfurogenes and Clostridium thermohydrosulfuricum produced ethanol and amylases with different components as primary metabolites of starch fermentation. Starch fermentation parameters were compared in mono- and cocultures of these two thermoanaerobes to show that the fermentation was dramatically improved as a consequence of coordinate action of amylolytic enzymes and synergistic metabolic interactions between the two species. Under given monoculture fermentation conditions, neither species completely degraded starch during the time course of the study, whereas in coculture, starch was completely degraded. In monoculture starch fermentation, C. thermohydrosulfuricum produced lower levels of pullulanase and glucoamylase, whereas C. thermosulfurogenes produced lower levels of β-amylase and glucoamylase. In coculture fermentation, improvement of starch metabolism by each species was noted in terms of increased amounts and rates of increased starch consumption, amylase production, and ethanol formation. The single-step coculture fermentation completely degraded 2.5% starch in 30 h at 60°C and produced 9 U of β-amylase per ml, 1.3 U of pullulanase per ml, 0.3 U of glucoamylase per ml, and > 120 mM ethanol with a yield of 1.7 mol/mol of glucose in starch. The potential industrial applications of the coculture fermentation and the physiological basis for the interspecies metabolic interactions are discussed.