Mixed Bacterial Strains Increase Cellulosic Ethanol Yield

A study published in the journal Biotechnology for Biofuels has identified new strains of fermenting bacteria that produce high ethanol yield from lignocellulosic biomass through a one-step bioconversion pathway called consolidated bioprocessing (CBP).

Traditional processes use the typical two-step conversion involving the breakdown of cellulosic materials by the addition of cellulase enzymes followed by sugar conversion into ethanol by means of fermenting yeast strains. CBP allows a direct one-step conversion that eliminates the addition of expensive cellulase enzymes. A group of researchers from the German company Direvo Industrial Biotechnology GmbH accomplished this by using mixtures of bacteria that produce lignocellulose-degrading enzymes and ferment the resulting sugars into ethanol, under high temperature conditions (>70 degrees Celsius).

In a preliminary screening, the researchers identified some environmental strains of thermophilic bacteria of the genus Caldicellulosiruptor and Thermoanaerobacter. These strains complement each other to degrade the cellulose and hemicellulose components of lignocellulosic biomass and to metabolize the sugar molecules containing 5 and 6 carbons. The subsequent experiments revealed that some dual co-cultures of Caldicellulosiruptor and Thermoanaerobacter strains produced higher concentrations of ethanol from 2 to 8 fold increase compared to single cultures.

The researchers concluded that these microbial mixtures provide an efficient CBP pathway for the production of second generation bioethanol or ethanol derived from lignocellulosic feedstock.