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Saccharomyces Cerevisiae for First and Second Generation Ethanol Production
Published in Devarajan Thangadurai, Jeyabalan Sangeetha, Industrial Biotechnology, 2017
Fernanda Bravim, Melina Campagnaro Farias, Oeber De Freitas Quadros, Patricia Machado Bueno Fernandes
Different pathways are available in nature for metabolism of arabinose and xylose; which are converted to xylulose 5-phosphate (intermediate compound) to enter the pentose phosphate pathway as shown in Figure 10.5. In yeasts, xylose is first reduced by xylose reductase to xylitol, which in turn is oxidized to xylulose by xylitol dehydrogenase. In bacteria and some anaerobic fungi, xylose isomerase is responsible for direct conversion of xylose to xylulose. Xylulose is finally phosphorylated to xylulose-5-phosphate by xylulokinase. In fungi, L-arabinose is reduced to L-arabitol (by arabinose reductase), L-xylulose (by arabitol dehydrogenase), xylitol (by L-xylulose reductase). Xylitol is finally converted to xylulose (by xylitol dehydrogenase), whose activity is also part of xylose utilization pathways. In bacteria, L-arabinose is converted to L-ribulose (by L-arabinose isomerase), L-ribulose-5-P (by L-ribulokinase) and finally D-xylulose-5-P (by L-ribulose-5-P 4-epimerase) (Bettiga et al., 2008).
Chitosan production by Penicillium citrinum using paper mill wastewater and rice straw hydrolysate as low-cost substrates in a continuous stirred tank reactor
Published in Environmental Technology, 2023
M.M.T. Namboodiri, Arul Manikandan, Tanushree Paul, Kannan Pakshirajan, G. Pugazhenthi
The effect of adding acetic acid at initial concentrations of 20, 50, 80, 100 and 150 mg L−1 to the paper mill wastewater supplemented with MSM revealed that 50 mg L−1 acetic acid is optimum for achieving a maximum COD removal of 67% and chitosan yield of 13.7% DCW. The enhancement in chitosan yield and COD removal from paper mill wastewater by P. citrinum due to acetic acid addition can be explained as follows. Paper and pulp wastewater contain cellulose, xylose and hemicellulose residues in low amounts along with the polymers lignin and phenolics. The high values of XR and XDH activity in the presence of acetic acid at low concentrations in this study suggest efficient utilization of xylose present in the wastewater, which subsequently enhanced the fungal growth. Xylose is first converted to xylulose by xylose reductase (XR), then converted to xylitol by xylitol dehydrogenase (XDH). Fructose 6-phosphate formed from xylitol acts as an important intermediate in hemicellulose utilization pathways, including accumulation of chitin and chitosan by fungi. The activities of XR and XDH were also high in the presence of acetic acid at low concentrations [18]. Other than acetic acid, compounds such as formic acid and furfurals at low concentrations in the media, enhance chitosan production by fungi.