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This study elucidated the importance of two critical enzymes in the regulation of butanol production in Clostridium acetobutylicum ATCC 824. Overexpression of both the 6-phosphofructokinase (pfkA) and pyruvate kinase (pykA) genes increased intracellular concentrations of ATP and NADH and also resistance to butanol toxicity. Marked increases of butanol and ethanol production, but not acetone, were also observed in batch fermentation. The butanol and ethanol concentrations were 29.4 and 85.5 % higher, respectively, in the fermentation by double-overexpressed C. acetobutylicum ATCC 824/pfkA+pykA than the wild-type strain. Furthermore, when fed-batch fermentation using glucose was carried out, the butanol and total solvent (acetone, butanol, and ethanol) concentrations reached as high as 19.12 and 28.02 g/L, respectively. The reason for improved butanol formation was attributed to the enhanced NADH and ATP concentrations and increased tolerance to butanol in the double-overexpressed strain.

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1,4-Dioxane-degrading bacterial consortia were enriched from forest soil (FS) and activated sludge (AS) using a defined medium containing 1,4-dioxane as the sole carbon source. These two enrichments cultures appeared to have inducible tetrahydrofuran/dioxane and propane degradation enzymes. According to qPCR results on the 16S rRNA and soluble di-iron monooxygenase genes, the relative abundances of 1,4-dioxane-degrading bacteria to total bacteria in FS and AS were 29.4% and 57.8%, respectively. For FS, the cell growth yields (Y), maximum specific degradation rate (V), and half-saturation concentration (K) were 0.58 mg-protein/mg-dioxane, 0.037 mg-dioxane/mg-protein∙h, and 93.9 mg/l, respectively. For AS, Y, V, and K were 0.34 mg-protein/mg-dioxane, 0.078 mg-dioxane/mg-protein∙h, and 181.3 mg/l, respectively. These kinetics data of FS and AS were similar to previously reported values. Based on bacterial community analysis on 16S rRNA gene sequences of the two enrichment cultures, the FS consortium was identified to contain 38.3% of and 10.6% of, similar to previously reported literature. Meanwhile, 49.5% of the AS consortium belonged to the candidate division TM7, which has never been reported to be involved in 1,4-dioxane biodegradation. However, recent studies suggested that TM7 bacteria were associated with degradation of non-biodegradable and hazardous materials. Therefore, our results showed that previously unknown 1,4-dioxane-degrading bacteria might play an important role in enriched AS. Although the metabolic capability and ecophysiological significance of the predominant TM7 bacteria in AS enrichment culture remain unclear, our data reveal hidden characteristics of the TM7 phylum and provide a perspective for studying this previously uncultured phylotype.

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Polyhydroxybutyrate (PHB) is a sought‐after alternative biopolymer to synthetics with its high biodegradability and similar properties to available polymers. However, its high production cost narrows its market application. In this study, cheap, biocompatible, and widely available fillers such as cellulose (CL) and calcium carbonate (CC) were incorporated into PHB using a heat‐assisted solution casting method to reduce the manufacturing cost of the bioplastic while retaining its properties. Characterization tests found that both natural fillers have relatively low miscibility with PHB which may be accounted for by self‐ and co‐agglomeration of the fillers while having improved thermal stability. The Young's modulus of the bioplastic films increased with the introduction of CC, while the mechanical property slightly decreased upon the addition of CL attributing to the aggregation of fillers. Full biodegradation of all composites within 8 weeks was observed in the compost biodegradability tests; PHB 90 CC 10 biodegraded the slowest after the 50th day, while PHB 90 CL 10 fully disintegrated after the 30th day. Further improvements such as the incorporation of cheap, naturally derived crosslinkers or plasticizers can greatly improve the properties of the synthesized biocomposites.