Abstract

Lignocellulosic materials are the most abundant renewable organic resources on the planet. In Brazil, sugar cane bagasse is one of the most studied residues with an estimated production of 174 million of metric tones correspondent to the 2013/2014 harvest year. As a result of the bagasse hydrolysis, it is obtained a mixture of pentoses and hexoses, especially glucose, xylose and arabinose. Although xylose is a major component of hemicellulose, and the second most abundant sugar in nature, its efficient use as carbon source for the production of microbial bio-products still represents a technical barrier. Ralstonia eutropha is the model organism for polyhydroxybutyrate (PHB) production but, it is not able to grow in xylose and only poor results were achieved when engineering its xylose catabolic pathway. Even though Burkholderia sacchari is the best-known PHB producer from xylose and sugar mixtures, the PHB conversion from xylose is about 40% lower than from glucose. D-Xylose assimilation in bacteria, through the pentose phosphate pathway, begins with its isomerization to D-xylulose by xylose isomerase (encoded by xylA), followed by a phosphorylation by xylulokinase (xylB) that produces D-xylulose 5-phosphate. The overexpression of genes involved in xylose metabolism, especially xylAB, has been proposed to increase the growth rate in xylose in different microorganisms. Within this context, in this work, we constructed a recombinant strain harboring xylA and xylB genes from B. sacchari. The xylAB fragment was expressed under its native promoters in a broad host range cloning vector pBBR1MCS-2. The recombinant plasmid pBBR1::xylABBS was used to construct B. sacchari LFM311 harboring multiple copies of xylAB genes. The recombinant strain and wild type reached specific growth rates in xylose of 0,23 and 0,18 h-1, respectively. These results represent an improvement of 17% in xylose consumption, suggesting that xylAB activity could be the bottleneck for xylose utilization in B. sacchari.