Engineered xylose utilization enhances bio-products productivity in the cyanobacterium Synechocystis sp. PCC 6803

Hydrolysis of plant biomass generates a mixture of simple sugars that is particularly rich in glucose and xylose. Fermentation of the released sugars emits CO2 as byproduct due to metabolic inefficiencies. Therefore, the ability of a microbe to simultaneously convert biomass sugars and photosynthetically fix CO2 into target products is very desirable. In this work, the cyanobacterium, Synechocystis 6803, was engineered to grow on xylose in addition to glucose. Both the xylA (xylose isomerase) and xylB (xylulokinase) genes from Escherichia coli were required to confer xylose utilization, but a xylose-specific transporter was not required. Introduction of xylAB into an ethylene-producing strain increased the rate of ethylene production in the presence of xylose. Additionally, introduction of xylAB into a glycogen-synthesis mutant enhanced production of keto acids. Isotopic tracer studies found that nearly half of the carbon in the excreted keto acids was derived from the engineered xylose metabolism, while the remainder was derived from CO2 fixation.