Manjula Senanayake

Oak Ridge National Laboratory

ABSTRACT

Lignocellulosic biomass, which consists of cellulose, hemicellulose and lignin, is a promising sustainable, carbon dioxide neutral and non-competitive energy resource. However, conversion to  bioenergy using traditional methods have proved to be less cost effective and energy efficient.  Several different biomass deconstruction approaches have been employed and the strong binding  between lignin and carbohydrate plant polymers has shown lignin recalcitrance issues have  severely hindered improvement in the bioconversion process. In order to reduce lignin  recalcitrance, transgenic poplar trees with lower lignin content have been developed. Here, we  probed the effects of QsuB regulation levels that produced three different transgenic species of  poplar trees with reduced lignin content and compared to the wildtype (WT). The level of QsuB  expression varied as Q1>Q15>Q5>WT. Biochemical study determined 15% less lignin and higher  hemicellulose content in Q1 and Q15 mutants compared to Q5 mutant and WT samples. Small angle neutron scattering (SANS) was used to study the effects of QsuB expression on the structure  and morphology of the cellulose microfibrils. Intact pieces of poplar stems were measured to  separate the anisotropic character of the plant cell wall from the isotropic; specifically, the  scattering features associated with the aligned arrangement of the cellulose microfibrils was  maintained to help separate from the amorphous polymer scattering. SANS model fitting results  illustrated that the cellulose microfibril cross-sectional sizes followed the relation  Q5=Q15=WT<Q1. Further, the distance between neighboring cellulose microfibrils progressively  increased with increasing QsuB expression levels and the highest expressed mutant Q1 showed no  regular order. Complementary to SANS, wide-angle X-ray scattering (WAXS) will be used to  determine cellulose crystallinity and microfibril orientation. Together, a comprehensive knowledge in the relation between QsuB expression levels and cellulose microfibril size and  arrangement in poplar stems will be achieved paving the way to develop a science-driven approach  to tune the characteristics of poplar stems to overcome recalcitrance and enhance biomass  conversion efficacy

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Email: senanayakemp@ornl.gov