A Mutant Caldicellulosiruptor bescii Unravels the Role of Pectin in Plant Biomass Recalcitrance

Plants are the most desired source of renewable energy and hydrocarbons because they fix CO2. Their structure, however, is a barrier to deconstruction, often referred to as recalcitrance. Members of the genus Caldicellulosiruptor are able to grow on unpretreated plant biomass and may provide an assay for plant deconstruction and biomass recalcitrance.

Using recent tools for gene manipulation, the team of Janet Westpheling from the University of Georgia developed a mutant Caldicellulosiruptor that does not have the genes for pectin degradation. The mutant produced had reduced ability to grow on both dicot and grass biomass, but grows normally on soluble sugars. Biomass from three plants, Arabidopsis (herbaceous dicot), switchgrass (monocot), and poplar (woody dicot), were then used to test the mutant in cell walls with different structures and compositions. The reduced growth of the mutant on all biomass types is evidence that pectin is vital in recalcitrance.

The simultaneous analysis of microbial digestion and plant biomass lets us identify plant wall structures that reduces the ability of microbes to deconstruct plant walls as well as identify enzymes that deconstruct those structures.