Abstract

The growing concern about reserve depletion and price fluctuation of oil as well as climate change, caused by the production of waste by this raw material, has resulted in several studies looking for more secure and renewable energy sources. Among these sources, lignocellulosic materials are the most abundant on the planet. Sugarcane bagasse is one of the most studied materials in Brazil, hoping to be used in various industrial processes, such as for the production of ethanol and polyhydroxyalkanoates (PHA), a family of polymers used in the creation of biodegradable plastics. In order to be used by microorganisms, that produce ethanol, PHA or other materials, lignocellulosic waste needs to be subjected to hydrolysis. As a result, cellulose and hemicellulose are released from the complex formed with the lignin, with subsequent breakdown of the sugar polymers, and release a mixture of pentoses and hexoses, mainly glucose, xylose and arabinose. Although xylose is a major component of lignocellulose and the second most abundant sugar in nature, its efficient use is still a technical barrier. In this context, a study was made with the xylose catabolism of Burkholderia sacchari, a very good PHA producer bacterium. A growth culture experiment in minimal medium, with xylose or glucose as the sole carbon source, demonstrated that this bacterium has a maximum specific growth rate (µmax) twice slow as in xylose (0,15h-1) than in glucose (0,41h-1). An in silico study was conducted, where the enzymes present in four different xylose pathways (Oxidutoreductase, Isomerase, Wiemberg and Dhams) described in literature, were used to identify which of them were encoded in B. sacchari genome. The isomerase pathway was found as the xylose metabolism pathway used by this bacterium, since xylA (xylose isomerase), xylB (xylulokinase) and xylFGH (ABC xylose transporter) were genes present in its genome. Some of the genes involved in the Wiemberg pathway were also found to have homologous genes in B. sacchari. It was possible to identify that just one gene of the Wiemberg pathway is missing in the B. sacchari genome, xylX (2-keto-3-deoxy-D-xylonate dehydratase). Products from each pathway are directed to the central metabolism of the bacteria through a diferent way, to the pentose phophate pathway, in the case of isomerase, and to the TCA cycle in Wiemberg’s. The genes of the other two pathways were not found in the B. sacchari genome. These results showed that the isomerase pathway for the xylose metabolism is present and probably active in B. sacchari. It also showed that a diferent pathway, Wiemberg, could be active if completed. Once each pathway enters the central metabolism in a diferent place, they could be used to produce diferent products like PHA. Modifications on those pathways are proposed in this work that can result on improvement in the bacterial efficiency in converting xylose to PHA.