Engineering of Corynebacterium glutamicum for utilization of hemicellulose as a carbon source

Abstract

Xylan is a major component of hemicellulose which is considered to be the second most abundant natural polymers in nature and it is regarded as one of the most important renewable resources. By enzymatic reaction, xylan can be degraded into xylose, its main building block, and then the resulting sugar (xylose) can be used as a major carbon source in the growth of microorganisms and further production of useful things. In this study, I engi-neered Corynenacterium glutamicum for the direct utilization of xylan as a carbon source. C. glutamicum is a Gram positive, non-sporulating bacteria and is also one of the most important bacteria in the industrial production of various chemicals and biomolecules including amino acids, lactate, and recombinant proteins. Overall scheme of this research was two-step process comprising (i) enzymatic hydrolysis of hemicellulose and (ii) xylose utilization as a carbon source by introducing heterologous xylose metabolic pathway. For the hydrolysis of xylan, two heterologous enzymes (endoxylanase and xylosidase) were expressed in C. glutamicum. The xylan can be decomposed into xylobiose or xylotriose by secreted endoxy-lanase in the media and then further hydrolyzed into xylose in the cytoplasm of cells. Due to the lack of xylose metabolic pathway, wild type of C. glutamicum cannot utilize the xylose as a carbon source. Next, to give the ability of xylose metabolism, heterologous cytoplasmic expression of the xylose isomerase (xylA) and xylulokinase (xylB) genes were introduced in C. glutamicum, mediating the conversion of xylose into xylulose 5-phosphate (an intermediate of the pentose phosphate pathway). As a result, xylose metabolism could be successfully introduced and I confirmed the cell growth by utilization of xylose as a carbon source in minimal media. Finally, two steps (xylan hydrolysis and xylose metabolism) were successfully combined as a whole cell system in which xylan can be directly utilized for growth of C. glutamicum.