Physicochemical Pretreatment of Vietnamosasa pusilla for Bioethanol and Xylitol Production

The consumption of fossil fuels has resulted in severe environmental consequences, including greenhouse gas emissions and climate change. Therefore, transitioning to alternative energy sources, such as cellulosic ethanol, is a promising strategy for reducing environmental impacts and promoting sustainable low-carbon energy. Vietnamosasa pusilla, an invasive weed, has been recognized as a high potential feedstock for sugar-based biorefineries due to its high total carbohydrate content, including glucan (48.1 ± 0.3%) and xylan (19.2 ± 0.4%). This study aimed to examine the impact of NaOH pretreatment-assisted autoclaving on V. pusilla feedstock. The V. pusilla enzymatic hydrolysate was used as a substrate for bioethanol and xylitol synthesis. After treating the feedstock with varying concentrations of NaOH at different temperatures, the glucose and xylose recovery yields were substantially higher than those of the untreated material. The hydrolysate generated by enzymatic hydrolysis was fermented into bioethanol using Saccharomyces cerevisiae TISTR 5339. The liquid byproduct of ethanol production was utilized by Candida tropicalis TISTR 5171 to generate xylitol. The results of this study indicate that the six- and five-carbon sugars of V. pusilla biomass have great potential for the production of two value-added products (bioethanol and xylitol).

Chromosomal mutations in Escherichia coli that improve tolerance to nonvolatile side-products from dilute acid treatment of sugarcane bagasse

Lignocellulosic biomass provides attractive nonfood carbohydrates for the production of ethanol, and dilute acid pretreatment is a biomass-independent process for access to these carbohydrates. However, this pretreatment also releases volatile and nonvolatile inhibitors of fermenting microorganisms. To identify unique gene products contributing to sensitivity/tolerance to nonvolatile inhibitors, ethanologenic Escherichia coli strain LY180 was adapted for growth in vacuum-treated sugarcane bagasse acid hydrolysate (VBHz) lacking furfural and other volatile inhibitors. A mutant, strain AQ15, obtained after approximately 500 generations of growth in VBHz, grew and fermented the sugars in a medium with 50% VBHz. Comparative genome sequence analysis of strains AQ15 and LY180 revealed 95 mutations in strain AQ15. Six of these mutations were also found in strain SL112, an independent inhibitor-tolerant derivative of strain LY180. Among these six mutations, null mutations in mdh and bacA were identified as contributing factors to VBHz tolerance in strain AQ15, based on the genetic and physiological analysis. The deletion of either gene in strain LY180 increased tolerance to VBHz from approximately 30-50% (vol/vol). Considering the location and physiological role of the two enzymes in the cell, it is likely that the two enzymes contribute to the VBHz sensitivity of ethanologenic E. coli by different mechanisms.

Rediscovering Acetate Metabolism: Its Potential Sources and Utilization for Biobased Transformation into Value-Added Chemicals

One of the great advantages of microbial fermentation is the capacity to convert various carbon compounds into value-added chemicals. In this regard, there have been many efforts to engineer microorganisms to facilitate utilization of abundant carbon sources. Recently, the potential of acetate as a feedstock has been discovered; efforts have been made to produce various biochemicals from acetate based on understanding of its metabolism. In this review, we discuss the potential sources of acetate and summarized the recent progress to improve acetate utilization with microorganisms. Furthermore, we also describe representative studies that engineered microorganisms for the production of biochemicals from acetate.