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Burkholderia Species
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Natalia Alvarez-Santullano, Pamela Villegas, Mario Sepúlveda, Ariel Vilchez, Raúl Donoso, Danilo Perez-Pantoja, Rodrigo Navia, Francisca Acevedo, Michael Seeger
In Paraburkholderia and Burkholderia strains, sucrose is hydrolyzed by sucrose hydrolase into glucose and fructose. Glucose catabolism is carried out through enzymes of the glycolysis, pentose phosphate, and ED pathways (Figure 5.4). Glucose is phosphorylated by glucokinase into glucose-6-phosphate, which undergoes oxidation by glucose-6-phosphate dehydrogenase with NADPH production and subsequent hydrolysis by 6-phosphogluconolactonase to yield gluconate-6-phosphate, which can be further degraded by the ED pathway or pentose phosphate pathway. Fructose is phosphorylated by fructokinase into fructose-6-phosphate, which may be isomerized into glucose-6-phosphate and channeled into gluconate-6-phosphate, entering the ED pathway or the pentose phosphate pathway. Xylose is transformed by xylose isomerase into xylulose and consequently converted by xylulokinase into xylulose 5-phosphate, entering the pentose phosphate pathway. Glycerol is transported through the membrane by glycerol facilitator (GlpF) and metabolized by glycerol kinase (GlpK) into glycerol-3-phosphate (G3P), which is converted by glycerol-3-phosphate dehydrogenase (GlpD) into dihydroxyacetone phosphate that is channeled into glycolysis. The substrate gluconate is phosphorylated by gluconokinase into gluconate-6-phosphate, which can be channeled into the pentose phosphate pathway or ED pathway. Most of the genomes of Paraburkholderia and Burkholderia strains reported for P(3HB) production (Table 5.1) possess the enzymes depicted in Figure 5.4.
Valorization of Hemicelluloses
Published in Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel, Hemicelluloses and Lignin in Biorefineries, 2017
Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel
In naturally D-xylose-utilizing bacteria, xylose is isomerized to D-xylulose by xylose-isomerase. Xylulose is then phosphorylated to xylulose 5-phosphate, which is an intermediate of the pentose phosphate pathway (PPP, secondary pathway for glucose metabolism). A similar pathway has been found in an anaerobic fungus; however, most naturally xylose-utilizing fungi contain a more complex pathway consisting of reduction–oxidation reactions involving the cofactors NAD(P)H and NAD(P)+. Xylose is reduced to xylitol by a xylose reductase (XR), and xylitol is then oxidized to D-xylulose by a xylitol dehydrogenase (XDH). As in bacteria, xylulose is phosphorylated to D-xylulose 5-phosphate by a xylulokinase (XK). The conversion of L-arabinose into intermediates of the PPP requires more enzymatic reactions than the conversion of xylose (Figure 9.3).
Hemicellulose Conversion to Ethanol
Published in Charles E. Wyman, Handbook on Bioethanol, 2018
Formation of Xylulose-5-Phosphate. The pathways by which xylose is converted to xylulose, shown in Figure 13.1, are significantly different in bacteria than in yeasts and fungi. Bacteria directly isomerize xylose to xylulose using the enzyme xylose isomerase. Yeasts and fungi use a two-step pathway in which xylose is first reduced by xylose reductase (XR) to xylitol, which is then oxidized to xylulose by xylitol dehydrogenase (XDH). For yeasts and fungi, the ability to convert xylose to X-5-P is strongly influenced by the cofactor specificity of XR. A comparative study of xylose-fermenting yeasts found that, during anaerobic fermentation of xylose, ethanol yield and production rate varied according to the level of NADH-linked XR activity [49].
Improved xylitol production by the novel inhibitor-tolerant yeast Candida tropicalis K2
Published in Environmental Technology, 2022
Anup Kumar Singh, Ajay Kumar Pandey, Mohit Kumar, Tanushree Paul, Naseem A. Gaur
Microbes such as yeast, bacteria and fungi have shown great potential for xylitol production utilizing xylose [11]. Xylose assimilating yeast converts D-xylose into xylitol in the presence of NAD(P)H-dependent xylose reductase (XR). Xylitol can be further converted into D-xylulose with NADH/NAD+ dependent xylitol dehydrogenase (XDH) and xylulose is converted to xylulose-5-phosphate in a phosphorylation reaction which finally enters into the pentose phosphate pathway [12,13]. Recently several yeast isolates were isolated from different environmental niches for xylitol production. Candida tropicalis YHJ1, isolated from a honey jar, produced 66.9 g/L of xylitol with the yield and productivities of 0.67 g/g and 0.47 g/L.h respectively from pure xylose during batch fermentation [14]. Meyerozyma guilliermondii UFV-1, isolated from the gut of Passalidae beetles, produced 51.88 g/L of xylitol with 0.67 g/g yield and 0.50 g/L.h productivity, respectively from pure xylose during batch fermentation [15]. Lignocellulosic biomass that has been widely reported such as corncob, sugarcane bagasse, rice straw and water hyacinth have also shown high potential for production of xylitol by Candida tropicalis [16–20]. C. tropicalis JA2, isolated from decaying wood and soil sample, produced 109.5 g/L of xylitol with a yield of 0.86 g/g and productivities of 2.81 g/L.h, respectively, from sugarcane bagasse during batch fermentation [21]. However, a maximum titre of 41 g/L xylitol was reported with non-detoxified corncob after 96 h of fermentation, with a yield of 0.73 g/g of xylose and along with a productivity of 0.43 g/L.h [22].
Production of chemicals in thermophilic mixed culture fermentation: mechanism and strategy
Published in Critical Reviews in Environmental Science and Technology, 2020
Kun Dai, Wei Zhang, Raymond Jianxiong Zeng, Fang Zhang
In the acidogenesis step (Figure 2), the thermophilic fermentative microorganisms convert the simple substrates of glucose and xylose into VFAs, alcohols, H2, and CO2 (Hoelzle, Virdis, & Batstone, 2014; Madigan, Martinko, Bender, Buckley, & Stahl, 2015; Regueira, González-Cabaleiro, Ofiţeru, Rodríguez, & Lema, 2018). Glucose is converted to pyruvate in the Embden-Meyerhof pathway (Equation (1)). Xylose is initially converted to D-xylulose-5-phosphate that is further converted to pyruvate and acetate through the pentose phosphate pathway (Equation (2)) and/or phosphoketolase pathway (Equation (3)).