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This study evaluated the compostability of rice straw as the main feedstock (75% in dry weight), supplemented with three different nitrogen-rich wastes, namely food waste (FW), dairy manure (DM), and sewage sludge (SS). Organic matter (OM) degradation, maturity and fertility of the end-product, and bacterial community structure during the composting processes were compared. All composting processes generated mature end-product within 51 days. Notably, FW addition was more effective to accelerate rice straw OM degradation and significantly improved end-product fertility with a high yield of Chinese cabbage. The succession of the bacterial community was accelerated with FW supplementation. Genera Geobacillus, Chryseolinea, and Blastocatella were significantly enriched during the composting of rice straw with FW supplementation. Finally, temperature, total nitrogen, moisture, pH, and total carbon were the key factors affecting microorganisms. This study provides a promising alternative method to enhance the disposal of larger amounts of rice straw in a shorter time.

This study evaluated the feasibility, system stability, and microbial community succession of thermophilic semi-continuous composting of kitchen waste (KW). The results revealed that treatment performance was stable at a 10 % feeding ratio, with an organic matter (OM) degradation efficiency of 81.5 % and seed germination index (GI) of 50.0 %. Moreover, the OM degradation efficiency and GI were improved to 83.4 % and 70.0 %, respectively, by maintaining an optimal compost moisture content (50-60 %). However, feeding ratios of ≥ 20 % caused deterioration of the composter system owing to OM overloading. Microbial community analysis revealed that Firmicutes, Actinobacteria, Chloroflexi, Proteobacteria, and Gemmatimonadetes were dominant. Additionally, moisture regulation significantly increased the Proteobacteria abundance by 57.1 % and reduced the Actinobacteria abundance by 57.8 %. Moreover, network analysis indicated that the bacterial community stability and positive interactions between genera were enhanced by moisture regulation. This information provides a useful reference for practical KW composting treatment in the semi-continuous mode.

Background Strong multiple stress-tolerance is a desirable characteristic for Saccharomyces cerevisiae when different feedstocks are used for economical industrial ethanol production. Random mutagenesis or genome shuffling has been applied for improving multiple stress-tolerance, however, these techniques are generally time-consuming and labor cost-intensive and their molecular mechanisms are unclear. Genetic engineering, as an efficient technology, is poorly applied to construct multiple stress-tolerant industrial S. cerevisiae due to lack of clear genetic targets. Therefore, constructing multiple stress-tolerant industrial S. cerevisiae is challenging. In this study, some target genes were mined by comparative transcriptomics analysis and applied for the construction of multiple stress-tolerant industrial S. cerevisiae strains with prominent bioethanol production. Results Twenty-eight shared differentially expressed genes (DEGs) were identified by comparative analysis of the transcriptomes of a multiple stress-tolerant strain E-158 and its original strain KF-7 under five stress conditions (high ethanol, high temperature, high glucose, high salt, etc.). Six of the shared DEGs which may have strong relationship with multiple stresses, including functional genes (ASP3, ENA5), genes of unknown function (YOL162W, YOR012W), and transcription factors (Crz1p, Tos8p), were selected by a comprehensive strategy from multiple aspects. Through genetic editing based on the CRISPR/Case9 technology, it was demonstrated that expression regulation of each of these six DEGs improved the multiple stress-tolerance and ethanol production of strain KF-7. In particular, the overexpression of ENA5 significantly enhanced the multiple stress-tolerance of not only KF-7 but also E-158. The resulting engineered strain, E-158-ENA5, achieved higher accumulation of ethanol. The ethanol concentrations were 101.67% and 27.31% higher than those of the E-158 when YPD media and industrial feedstocks (straw, molasses, cassava) were fermented, respectively, under stress conditions. Conclusion Six genes that could be used as the gene targets to improve multiple stress-tolerance and ethanol production capacities of S. cerevisiae were identified for the first time. Compared to the other five DEGs, ENA5 has a more vital function in regulating the multiple stress-tolerance of S. cerevisiae. These findings provide novel insights into the efficient construction of multiple stress-tolerant industrial S. cerevisiae suitable for the fermentation of different raw materials. Graphical Abstract Supplementary Information The online version contains supplementary material available at 10.1186/s13068-022-02109-x., Highlights Novel genes related to stress tolerance were mined by a comprehensive strategy. Stress tolerance was improved by regulating expression of each of the novel genes. Overexpression of ENA5 enhanced ethanol production under all stress conditions. Ethanol titer of the engineered strain increased by 41.35% at high temperature. Ethanol titer of the engineered strain increased by 121.42% at salt stress condition Supplementary Information The online version contains supplementary material available at 10.1186/s13068-022-02109-x.

The co-production of xylitol and ethanol from agricultural straw has more economic advantages than the production of ethanol only. Saccharomyces cerevisiae, the most widely used ethanol-producing yeast, can be genetically engineered to ferment xylose to xylitol. In the present study, the effects of xylose-specificity, cofactor preference, and the gene copy number of xylose reductase (XR; encoding by XYL1 gene) on xylitol production of S. cerevisiae were investigated. The results showed that overexpression of XYL1 gene with a lower xylose-specificity and a higher NADPH preference favored the xylitol production. The copy number of XYL1 had a positive correlation with the XR activity but did not show a good correlation with the xylitol productivity. The overexpression of XYL1 from Candida tropicalis (CtXYL1) achieved a xylitol productivity of 0.83 g/L/h and a yield of 0.99 g/g-consumed xylose during batch fermentation with 43.5 g/L xylose and 17.0 g/L glucose. During simultaneous saccharification and fermentation (SSF) of pretreated corn stover, the strain overexpressing CtXYL1 produced 45.41 g/L xylitol and 50.19 g/L ethanol, suggesting its application potential for xylitol and ethanol co-production from straw feedstocks.

The growth and ethanol fermentation of Saccharomyces cerevisiae are vulnerable to weak acid that coexists with sugar in lignocellulosic hydrolysate. In this study, the molecular basis of S. cerevisiae in response to acetic and formic acids was investigated when fermented with glucose and xylose at pH 5.0. Transcriptional profiling revealed that 294 (657 in total) differentially expressed genes (DEGs) were exclusive to mixed acetic and formic acids (Aa_Fa) group, the DEGs in acetic acid (Aa) and formic acid (Fa) group were 308 and 326, respectively. The general responses to Aa, Fa, and Aa_Fa mainly involved carbohydrate metabolism, amino acid metabolism, transcriptional regulation, and stress response. In Aa_Fa group, the enrichment ratio of each pathway was much higher than being exposed to Aa or Fa stress individually, and some enrichments not existed in Aa or Fa group were observed, suggesting the synergistic anti-inhibition responses of S. cerevisiae was triggered. In yeast cells, bioconversion, stress response, and transmembrane transport could be activated to resist acetic and formic acids accompanying with energy consumption. Except the putative transcriptional factor (TF) - Haa1p, the other three TFs, Hap4p, Yox1p, and Mag1p, might as well be considered to participate in acetic and formic acids resistance responses.

A heterologous xylose utilization pathway, either xylose reductase-xylitol dehydrogenase (XR-XDH) or xylose isomerase (XI), is usually introduced into Saccharomyces cerevisiae to construct a xylose-fermenting strain for lignocellulosic ethanol production. To investigate the molecular basis underlying the effect of different xylose utilization pathways on the xylose metabolism and ethanol fermentation, transcriptomes of flocculating industrial strains with the same genetic background harboring different xylose utilization pathways were studied. A different source of xylA did not obviously affect the change of the strains transcriptome, but compared with the XR-XDH strain, several key genes in the central carbon pathway were downregulated in the XI strains, suggesting a lower carbon flow to ethanol. The carbon starvation caused by lower xylose metabolism in XI strains further influenced the stress response and cell metabolism of amino acid, nucleobase, and vitamin. Besides, the downregulated genes mostly included those involved in mitotic cell cycle and the cell division-related process. Moreover, the transcriptomes analysis indicated that the after integrate xylA in the δ region, the DNA and chromosome stability and cell wall integrity of the strains were affected to some extent. The aim of this was to provide some reference for constructing efficient xylose-fermenting strains.

Background Renewable chemicals have attracted attention due to increasing interest in environmental concerns and resource utilization. Biobased production of industrial compounds from nonfood biomass has become increasingly important as a sustainable replacement for traditional petroleum-based production processes depending on fossil resources. Therefore, we engineered an Enterobacter cloacae budC and ldhA double-deletion strain (namely, EC∆budC∆ldhA) to redirect carbon fluxes and optimized the culture conditions to co-produce succinic acid and acetoin. Results In this work, E. cloacae was metabolically engineered to enhance its combined succinic acid and acetoin production during fermentation. Strain EC∆budC∆ldhA was constructed by deleting 2,3-butanediol dehydrogenase (budC), which is involved in 2,3-butanediol production, and lactate dehydrogenase (ldhA), which is involved in lactic acid production, from the E. cloacae genome. After redirecting and fine-tuning the E. cloacae metabolic flux, succinic acid and acetoin production was enhanced, and the combined production titers of acetoin and succinic acid from glucose were 17.75 and 2.75 g L−1, respectively. Moreover, to further improve acetoin and succinic acid production, glucose and NaHCO3 modes and times of feeding were optimized during fermentation of the EC∆budC∆ldhA strain. The maximum titers of acetoin and succinic acid were 39.5 and 20.3 g L−1 at 72 h, respectively. Conclusions The engineered strain EC∆budC∆ldhA is useful for the co-production of acetoin and succinic acid and for reducing microbial fermentation costs by combining processes into a single step.

BackgroundXylitol accumulation is a major barrier for efficient ethanol production through heterologous xylose reductase-xylitol dehydrogenase (XR-XDH) pathway in recombinantSaccharomyces cerevisiae. Mutated NADH-preferring XR is usually employed to alleviate xylitol accumulation. However, it remains unclear how mutated XR affects the metabolic network for xylose metabolism. In this study, haploid and diploid strains were employed to investigate the transcriptional responses to changes in cofactor preference of XR through RNA-seq analysis during xylose fermentation.ResultsFor the haploid strains, genes involved in xylose-assimilation (XYL1,XYL2,XKS1), glycolysis, and alcohol fermentation had higher transcript levels in response to mutated XR, which was consistent with the improved xylose consumption rate and ethanol yield. For the diploid strains, genes related to protein biosynthesis were upregulated while genes involved in glyoxylate shunt were downregulated in response to mutated XR, which might contribute to the improved yields of biomass and ethanol. When comparing the diploids with the haploids, genes involved in glycolysis and MAPK signaling pathway were significantly downregulated, while oxidative stress related transcription factors (TFs) were significantly upregulated, irrespective of the cofactor preference of XR.ConclusionsOur results not only revealed the differences in transcriptional responses of the diploid and haploid strains to mutated XR, but also provided underlying basis for better understanding the differences in xylose metabolism between the diploid and haploid strains.

Engineered Saccharomyces cerevisiae can reduce xylose to xylitol. However, in S.cerevisiae, there are several endogenous enzymes including xylitol dehydrogenase encoded by XYL2, sorbitol dehydrogenases encoded by SOR1/SOR2 and xylulokinase encoded by XKS1 may lead to the assimilation of xylitol. In this study, to increase xylitol accumulation, these genes were separately deleted through CRISPR/Cas9 system. Their effects on xylitol yield of an industrial S. cerevisiae CK17 overexpressing Candida tropicalis XYL1 (encoding xylose reductase) were investigated. Deletion of SOR1/SOR2 or XKS1 increased the xylitol yield in both batch and fed-batch fermentation with different concentrations of glucose and xylose. The analysis of the transcription level of key genes in the mutants during fed-batch fermentation suggests that SOR1/SOR2 are more crucially responsible for xylitol oxidation than XYL2 under the genetic background of S.cerevisiae CK17. The deletion of XKS1 gene could also weaken SOR1/SOR2 expression, thereby increasing the xylitol accumulation. The XKS1-deleted strain CK17ΔXKS1 produced 46.17 g/L of xylitol and reached a xylitol yield of 0.92 g/g during simultaneous saccharification and fermentation (SSF) of pretreated corn stover slurry. Therefore, the deletion of XKS1 gene provides a promising strategy to meet the industrial demands for xylitol production from lignocellulosic biomass.

This paper proposes the classification algorithm of news pages based on domain Ontology. In order to improve the shortage of current classification algorithm that only considers the content similarity, this paper presents the semantic classification method which considers both content similarity and structural correlation. Firstly, it parses the Ontology to get Ontology category vector, extracts keywords of news pages texts and drops semantic dimension. At this time, finding out the same vocabulary and ontology category vector in page texts to constitute the text expectation vector, and then calculating the content similarity between ontology category vector and expectation vector of text by using the law of cosines. Secondly, the common vocabularies are mapped to the ontology hierarchy chart, and the structural relevancy is obtained by calculating weighted path of this directed acyclic graph. Finally, it calculates the correlation degree of the news pages and Ontology by combining both, and determines the category of news pages by judging the size relationship between the result and the initial threshold value.

This paper introduces a traditional method of concept extraction. Considered some defects which this method will miss some concepts having synonyms and the relationship of “is-a”. It gives the improved algorithm to extract them. The result of the experiment shows the feasibility of this method.

In this information society, the traditional method of ontology construction can’t meet the demand for researchers. Because it’s a difficult task to build ontology by hands. The research of automatical construction of ontology is still in the primary stage, especially in the law field. Considering the above condition, this paper gives a Research on Ontology Construction Automatically in the Law Field; we put forward the method of using LLR formula in the step of term abstraction to improve the precision and applying K-means clustering algorithm to obtain better relations of concepts hierarchy. Compared with the approach of constructing ontology by hands, it gets better effect on the law ontology.