Schizosaccharomyces pombe as an Efficient Yeast to Convert Sugarcane Bagasse Pretreated with Ionic Liquids in Ethanol

The deletion of Schizosaccharomyces pombe decreased the production of flavor-related metabolites during traditional Baijiu fermentation

The microbiota in traditional solid-state fermentation is a complex microbiota that plays a key role in the production of feed, fuel, food and pharmaceutical products. The function of microbiota is an important factor dictating the quantity and quality of products. Core functional species play key metabolic roles in the microbiota, and their disappearance could result in the abnormal fermentation process. In this work, we combined Baijiu production and laboratory experiments to explore the keystone microbes and their metabolites. We found the deletion of core functional microbe resulted in the loss of multiple metabolites involved many alcohols and acids. In the traditional Baijiu production, the absence or appearance of Schizosaccharomyces pombe caused the content divergence in 227 flavor-related metabolites, especially in ethanol, butanol and pentanoic acid between abnormal and normal group (each content > 1 mg/kg and the content ratio of normal/abnormal group > 2). Schi. pombe increased the expression level of related genes involving alcohol dehydrogenase (ADH), acyl-CoA oxidase (ACOX) and trans-2-enoyl-CoA reductase (TER). Moreover, in the verification experiment of laboratory, the absence or appearance of Schizosaccharomyces pombe C-11 caused the content divergence in 136 flavor-related metabolites, especially in ethanol, butanol and pentanoic acid between Sp- and Sp+ group (each content > 1 mg/kg and the content ratio of Sp+/Sp- group > 2). Our results identified specific member that were essential for the function of fermentation microbiota. This study also suggests species deletions from fermentation microbiota and synthetic consortium could be a useful approach to illustrate relevant microbe-metabolites association and defining metabolic roles in the traditional solid-state fermentation.

Robust microorganisms for biofuel and chemical production from municipal solid waste

Background

Worldwide 3.4 billion tonnes of municipal solid waste (MSW) will be produced annually by 2050, however, current approaches to MSW management predominantly involve unsustainable practices like landfilling and incineration. The organic fraction of MSW (OMSW) typically comprises ~ 50% lignocellulose-rich material but is underexplored as a biomanufacturing feedstock due to its highly inconsistent and heterogeneous composition. This study sought to overcome the limitations associated with studying MSW-derived feedstocks by using OMSW produced from a realistic and reproducible MSW mixture on a commercial autoclave system. The resulting OMSW fibre was enzymatically hydrolysed and used to screen diverse microorganisms of biotechnological interest to identify robust species capable of fermenting this complex feedstock.

Results

The autoclave pre-treated OMSW fibre contained a polysaccharide fraction comprising 38% cellulose and 4% hemicellulose. Enzymatic hydrolysate of OMSW fibre was high in d-glucose (5.5% w/v) and d-xylose (1.8%w/v) but deficient in nitrogen and phosphate. Although relatively low levels of levulinic acid (30 mM) and vanillin (2 mM) were detected and furfural and 5-hydroxymethylfurfural were absent, the hydrolysate contained an abundance of potentially toxic metals (0.6% w/v). Hydrolysate supplemented with 1% yeast extract to alleviate nutrient limitation was used in a substrate-oriented shake-flask screen with eight biotechnologically useful microorganisms (Clostridium saccharoperbutylacetonicum, Escherichia coli, Geobacillus thermoglucosidasius, Pseudomonas putida, Rhodococcus opacus, Saccharomyces cerevisiae, Schizosaccharomyces pombe and Zymomonas mobilis). Each species’ growth and productivity were characterised and three species were identified that robustly and efficiently fermented OMSW fibre hydrolysate without significant substrate inhibition: Z. mobilis, S. cerevisiae and R. opacus, respectively produced product to 69%, 70% and 72% of the maximum theoretical fermentation yield and could theoretically produce 136 kg and 139 kg of ethanol and 91 kg of triacylglycerol (TAG) per tonne of OMSW.

Conclusions

Developing an integrated biorefinery around MSW has the potential to significantly alleviate the environmental burden of current waste management practices. Substrate-oriented screening of a representative and reproducible OMSW-derived fibre identified microorganisms intrinsically suited to growth on OMSW hydrolysates. These species are promising candidates for developing an MSW biorefining platform and provide a foundation for future studies aiming to valorise this underexplored feedstock.