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[Display omitted] • pflA knockout enhanced ethanol tolerance and production in T. aotearoense SCUT27/ Δldh. • The ethanol/acetate ratio increased 2.16-fold when compared to the parental strain. • Oxidative decarboxylation of pyruvate via Pfor is favorable over Pfl for ethanol production. • Immobilized-cell fermentation was employed to further improve the ethanol production. • The highest ethanol production (45.01 g/L) in T. aotearoense SCUT27 was obtained. Thermophilic anaerobic bacteria have received increasing interest as a promising bioprocessing platform for bioethanol production due to their broad substrate range and higher operating temperature. However, ethanol concentration is still lower than the commercial requirements on account of the high by-product formation and low ethanol tolerance. Our previous transcriptome analysis showed the gene expression level of pyruvate formate lyase-activating protein (PflA) was significantly down-regulated when Thermoanaerobacterium aotearoense SCUT27/ Δldh was stimulated by various concentrations of ethanol. Based on this, we constructed the mutant strain T. aotearoense SCUT27/ Δldh / ΔpflA , which not only possesses higher ethanol tolerance and production but also has enhanced ethanol/acetate ratio that is important for economical ethanol production. Compared to T. aotearoense SCUT27/ Δldh , the mutant strain could resist to 5% (v/v) exogenous ethanol and produce 49 % more ethanol (38.82 g/L vs. 26.05 g/L) in 5-L bioreactor. In addition, the final concentration of ethanol reached 45.01 g/L by immobilized cell fermentation, which is the highest value obtained in T. aotearoense SCUT27. Simultaneously, the ethanol/acetate ratio of the mutant strain achieved 6.82, which was 2.16-fold higher than that of the parental strain. [ABSTRACT FROM AUTHOR]

Bioethanol is a renewable biofuel that has a strong inhibitory effect on cells in bioethanol fermentation by yeast. In this study, carbon nanotube (CNT)-mixed polydimethylsiloxane (PDMS) membranes were used for ethanol recovery from model solutions as well as for fermentation by self-flocculating yeast. Imbedding CNTs into the PDMS membrane led to enhanced ethanol recovery, with a maximum total flux of 128.7 g/m 2 h and an ethanol titer of 615.1 g/L in permeate. The CNTs can provide a flexible route for ethanol transport through the inner tubes or along the smooth surface. In fed-batch fermentation incorporating pervaporation, 112.3 g/L of ethanol was produced with an overall ethanol productivity and yield of 2.23 g/L h and 0.45 g/g, respectively. The membrane produced a highly concentrated condensate containing 400.3–487.5 g/L of ethanol. Furthermore, as yeast flocs can be throttled down in the bioreactor, self-flocculating yeast can be used to prevent membrane fouling induced by cell adsorption on the membrane. Therefore, the CNT-mixed membrane coupled with ethanol fermentation by self-flocculating yeast not only reduces ethanol-mediated inhibition of cells but also saves the production cost because of the reduced fouling risk. Thus, this combination approach has potential in industrial bioethanol production for long-time operation. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the work was to study the properties of the bacterial cellulose membrane (BCM) and the feasibility of using it as a new, environmentally friendly support carrier for yeast cell immobilization. It was observed that the morphology of BCM varied with different cultivation methods and the scanning electron microscopy (SEM) images confirmed that the yeast cells were entrapped in the porous network of BCM obtained from the static culture and stabilized by the cross-linked fibrils. Particularly, the research confirmed the effectiveness of yeast immobilization in BCM reflected by the high yield of alcohol (9.7% v/v, a 21.25% increase of those using free cells) and the high stability. The specific rate of ethanol production by the immobilized cells in BCM was 2.1gg−1 h−1, 31.3% greater than that of the suspended cells. Results implied that applying BCM as the support carrier had little adverse effects on cell viability and proliferation. Instead, it facilitated the product leakage and nutrients transportation through the porous network. [Copyright &y& Elsevier]