Digestibility of Wheat and Cattail Biomass Using a Co-culture of Thermophilic Anaerobes for Consolidated Bioprocessing

Abstract

Alternative low-carbon transportation fuels, such as biofuels, are needed to replace or supplement fossil fuels in order to lower global greenhouse gas emissions and combat climate change. Lignocellulosic biofuels have relatively low carbon emissions and are created using the non-food parts of crops and other plants, such as the leaves and stems, which are comprised mostly of a tough material called lignocellulose, composed of cellulose, hemicellulose, and lignin. One of the best lignocellulose degraders found in nature that is also capable of fermenting the released sugars to ethanol is Clostridium thermocellum, although improvements in both lignocellulose hydrolysis extent and ethanol yields are needed for commercial viability.C. thermocellum, considered a cellulose-degrading specialist, was co-cultured with two different hemicellulose-specialists, C. stercorarium and Thermoanaerobacter thermohydrosulfuricus. The hypothesis was that the co-cultures might degrade more lignocellulose owing to the additional hydrolytic enzymes supplied by the partners and their ability to uptake the inhibitory hemicellulose sugars. All co-culture combinations were found to solubilize more wheat straw, among other lignocellulose materials, and produce more endproducts, including ethanol, than C. thermocellum alone. These co-cultures were stable over multiple serial passages, on either wheat straw or pure cellulose, although some evidence of carbon competition was observed. The tri-culture was successfully used to screen the digestibility of various lignocellulose materials, revealing substantial difference between cattail harvested in different seasons. Cross-feeding of vital growth factors was observed between the various co-culture members in a defined medium.The metabolism of C. thermocellum is atypical compared to many organisms, including the absence of a pyruvate kinase, and its substitution with both a malate shunt and a putative Thank you to my friends and family for always supporting me along this journey. I would like to thank my supervisor, Dr. Richard Sparling, for giving me this opportunity and for his incredibly valuable guidance and mentorship, the strict scientific rigour helped me develop my critical thinking skills.

Composition of Lignocellulose Hydrolysate in Different Biorefinery Strategies: Nutrients and Inhibitors

“…In such cases, CBP hosts are required to be modified by genetic engineering or metabolic engineering [32,193,194]. Another approach is the co-culture strategy by introducing other strains to metabolize these sugars and fully utilizing various carbohydrates in the lignocellulosic hydrolysates, thus improving the hydrolysis efficiency of upstream strains [191,195,196]. However, this approach has its challenges, as the growth conditions in the co-culture system should meet the requirements for all different microorganisms (such as pH, oxygen, and temperature) and the growth of one species does not have toxic or inhibitory effects on others [197].…”

A Review on Bacterial Contribution to Lignocellulose Breakdown into Useful Bio-Products

“…Monoculture approach was compared to a co-culture ( Clostridium thermocellum , C. stercorarium , and Thermoanaerobacter thermohydrosulfuricus ) using different biomass. The co-culture showed more promise in digesting biomass [ 115 ]. Using mixed cultures to degrade lignocellulose comes from an understanding that lignin in nature is not removed by a single species.…”