Abstract
Wood sugars such as xylose can be used as an inexpensive carbon source for biotechnological applications. The model cyanobacterium Synechocystis sp. PCC 6803 lacks the ability to catabolize wood sugars as an energy source. Here, we generated four Synechocystis strains that heterologously expressed XylAB enzymes, which mediate xylose catabolism, either in combination with or without one of three xylose transporters, namely XylE, GalP, or Glf. Except for glf, which is derived from the bacterium Zymomonas mobilis ZM4, the heterologous genes were sourced from Escherichia coli K-12. All of the recombinant strains were able to utilize xylose in the absence of catabolite repression. When xylose was the lone source of organic carbon, strains possessing the XylE and Glf transporters were most efficient in terms of dry biomass production and xylose consumption and the strain lacking a heterologous transporter was the least efficient. However, in the presence of a xylose-glucose mixed sugar source, the strains exhibited similar levels of growth and xylose consumption. This study demonstrates that various bacterial xylose transporters can boost xylose catabolism in transgenic Synechocystis strains, and paves the way for the sustainable production of bio-compounds and green fuels from lignocellulosic biomass.
Highlights
Lignocellulosic material is an abundant, inexpensive, and renewable source of carbon with potential industrial applications (Ragauskas et al, 2006)
The plasmid constructs designed for integration of the transporter genes included the psbA2 promoter of Synechocystis origin, 5ST1T2 double terminator of E. coli origin, kanamycin resistance cassette, neutral site 1 divided into ∼600 bp upstream and ∼600 bp downstream regions, and one of the three aforementioned transporter genes (Figure 2A)
In the second round of transformation, the xylAB genes, which are responsible for funneling xylose into the phosphate pathway (PPP), were introduced into neutral site 2 (Kunert et al, 2000) in the three Synechocystis strains generated in the first round of transformation as well as in the WT strain via homologous recombination to obtain four
Summary
Lignocellulosic material is an abundant, inexpensive, and renewable source of carbon with potential industrial applications (Ragauskas et al, 2006). Large quantities of lignocellulosic biomass are generated in agricultural, forestry, and related industries each year. This residual biomass can be used to synthesize a number of value-added products (Pothiraj et al, 2006), especially energy-rich compounds that can be used as biofuels (Ragauskas et al, 2006; Lee and Lavoie, 2013; Anwar et al, 2014). Hydrolysis of lignocellulose yields xylose, which is the second most abundant sugar in the biosphere after glucose. Xylose is isomerized by Engineering Synechocystis for Xylose Utilization
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