Abstract
Lignocellulosic biomass can serve as an inexpensive and renewable source of carbon for the biosynthesis of commercially important compounds. L-arabinose is the second most abundant pentose sugar present in the plant materials. Model cyanobacterium Synechocystis sp. PCC 6803 is incapable of catabolism of L-arabinose as a source of carbon and energy. In this study, all the heterologous genes expressed in Synechocystis were derived from Escherichia coli K-12. Initially we constructed four Synechocystis strains that expressed AraBAD enzymes involved in L-arabinose catabolism, either in combination with or without one of the three arabinose transporters, AraE, AraFGH or AraJ. Among the recombinants, the strain possessing AraJ transporter was observed to be the most efficient in terms of dry biomass production and L-arabinose consumption. Later, an additional strain was generated by the expression of AraJ in the AraE-possessing strain. The resultant strain was shown to be advantageous over its parent. This study demonstrates that AraJ, a protein with hitherto unknown function plays a role in the uptake of L-arabinose to boost its catabolism in the transgenic Synechocystis strains. The work also contributes to the current knowledge regarding metabolic engineering of cyanobacteria for the utilization of pentose sugars.
Highlights
Biomass is an abundant and renewable raw material that can be converted into a number of useful products, transportation fuels and direct energy (Ragauskas et al 2006)
In the subsequent round of transformation, four recombinant strains were generated by inserting the araBAD gene set of E. coli K-12 origin into the three strains generated in the first round of transformation and the Wild-type strain (WT) strain
As in our previously reported xylose work (Ranade et al 2015), E. coli was chosen as the source organism for the arabinose-specific genes, which were expressed under the control of a native light-dependent promoter, psbA2 (Mohamed and Jansson 1989; Lindberg et al; 2010)
Summary
Biomass is an abundant and renewable raw material that can be converted into a number of useful products, transportation fuels and direct energy (Ragauskas et al 2006). Hemicelluloses which comprise of heterogeneous polymers of pentoses, hexoses, and organic acids represent about 20–35% of the total lignocellulosic biomass (Saha 2003). Xylose stands out as the predominant pentose sugar in the hardwood hemicelluloses. L-arabinose is one of the major pentose sugars in the leaves of grass and other herbaceous species, and in agricultural residues such as rapeseed meal, corn fibre, barley straw, rice straw, wheat bran etc. In the first step after transportation, L-arabinose is isomerized to L-ribulose by the action of AraA (L-arabinose isomerase). L-Ru5P is converted by AraD (L-ribulose-5-phosphate 4-epimerase) to a pentose phosphate
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