Plant genetic engineering for biofuel production- a problem solver from the root

"Genetically engineering plants to produce cellulases and hemicellulases, and to reduce the need for pretreatment processes through lignin modification, are promising paths to solving this problem, together with other strategies, such as increasing plant polysaccharide content and overall biomass." A review paper published in Nature summarized the research progress in these aspects.

Cheap sugar: How can it be cheaper?

It is known that feedstock cost account for significant part of overall ethanol production cost. The key is to obtain cheap fermentable monomer sugars from lignocellulosic biomass with the following factors:
· Monomer sugar recovery yield. If we look at biomass, only ~65-70% of cell wall is carbohydrate that is our target to convert into monomer sugars. The question is how to efficiently hydrolyze it with high yield. Chemically or enzymatically? Currently both cannot achieve high sugar yield and high efficiency. The combination of chemical and enzymatical hydrolysis is the direction. However, more factors need to be considered to achieve high sugar yield when talking about a commercialized technology:
o Recoverable/recyclable chemicals that minimize the chemical cost and waste treatment
o The pH of pretreatment that impacts reactor metallurgy
o The temperature of pretreatment that impacts energy usage
o The robust of enzymes that reduce the loading and increase the efficiency

Effects of Cellulose Crystallinity, Hemicellulose, and Lignin on the Enzymatic Hydrolysis

It is known that the efficiency of enzymatic hydrolysis was affected by the degree of cellulose crystallinity, hemicellulose and lignin removal. A recent published paper reported the results on how these factors impacted enzymatic hydrolysis.

Prefermentation: an approach to improve co-fermentation in SSF

Prefermentation was reported as a possible means to overcome the problem of competitive
inhibition fron glucose on xylose: i.e. the free hexoses initially present in the slurry, were fermented before adding enzymes.

Silica bodies: possible physical barriers to chemical penetration during pretreatment

It is known silica content is high for non-woody lignocellulosic biomass.The deposition of silica bodies in biologically engineered craters was found to be a unique feature, which leads to some silica-rich spots on the surface of cell wall. On one hand, the silica will cause scaling problems if not treated properly; on the other hand, they also become barriers for chemical pretreatment. It is neccessary to dissolve the silica through pretreatment. Therefore, the chemicals used and the pH for pretreatment need to be chosen carefully.