Pentose sugars are increasingly being used in industrial applications of Saccharomyces cerevisiae. Although l-arabinose is a highlighted pentose that has been identified as next-generation biomass, arabinose fermentation has not yet undergone extensive development for industrial utilization. In this study, we integrated a heterologous fungal arabinose pathway with a deletion of PHO13 phosphatase gene. PHO13 deletion increased arabinose consumption rate and specific ethanol productivity under aerobic conditions and consequently depleted sedoheptulose by activation of the TAL1 gene. Global metabolite profiling indicated upregulation of the pentose phosphate pathway and downstream effects such as trehalose accumulation and downregulation of the TCA cycle. Our results suggest that engineering of PHO13 has ample potential for arabinose conversion to ethanol as an industrial source for biofuels.
Use of raw feedstuffs for livestock is limited by low digestibility. Recently, fermentation of feedstuffs has been highlighted as a new way to improve nutrient absorption through the production of organic acids using inoculated microorganisms, which can also play a probiotic role. However, standard procedures for feedstuff fermentation have not been clearly defined because the process is influenced by climatic variation, and an analytical standard for fermented feedstuffs is lacking. This study aimed to evaluate the microbiological and biochemical changes of feedstuffs during fermentation at temperatures corresponding to different seasons (10℃, 20℃, 30℃, and 40℃). We also investigated the effects of yeast, lactic acid bacteria (LAB), and Bacillus spp. on fermentation and determined the results of their interactions during fermentation. The viable cells were observed within 8 days in single-strain fermentation. However, when feedstuffs were inoculated with a culture of mixed strains, LAB were predominant at low temperatures (10℃ and 20℃), while Bacillus spp. was predominant at high temperatures (30℃ and 40℃). A significant drop in pH from 6.5 to 4.3 was observed when LAB was the dominant strain in the culture, which correlated with the concentrations of lactic acid. Slight ethanol production was detected above 20℃ regardless of the incubation temperature, suggesting active metabolism of yeast, despite this organism making up a marginal portion of the microbes in the mixed culture. These results suggested that fermentation temperature significantly affects microbiological profiles and biochemical parameters, such as pH and the lactic acid concentration, of fermented feedstuffs. Our data provide valuable information for the determination of industrial standards for fermented feedstuffs.
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