High temperature inhibits cell growth and ethanol fermentation of Saccharomyces cerevisiae. As a complex phenotype, thermotolerance usually involves synergistic actions of many genes, thereby being difficult to engineer. The overexpression of either endogenous or exogenous stress-related transcription factor genes in yeasts was found to be able to improve relevant stress tolerance of the hosts.To increase ethanol yield of high-temperature fermentation, we constructed a series of strains of S. cerevisiae by expressing 8 transcription factor genes from S. cerevisiae and 7 transcription factor genes from thermotolerant K. marxianus in S. cerevisiae. The results of growth curve measurements and spotting test show that KmHsf1 and KmMsn2 can enhance cell growth of S. cerevisiae at 40–42 °C. According to the results of batch fermentation at 43 °C with an initial glucose concentration of 104.8 g/l, the fermentation broths of KmHSF1 and KmMSN2-expressing strains could reach final ethanol concentrations of 27.2 ± 1.4 and 27.6 ± 1.2 g/l, respectively, while the control strain just produced 18.9 ± 0.3 g/l ethanol. Transcriptomic analysis found that the expression of KmHSF1 and KmMSN2 resulted in 55 (including 31 up-regulated and 24 down-regulated) and 50 (including 32 up-regulated and 18 down-regulated) genes with different expression levels, respectively (padj < 0.05). The results of transcriptomic analysis also reveal that KmHsf1 might increase ethanol production by regulating genes related to transporter activity to limit excessive ATP consumption and promote the uptake of glucose; while KmMsn2 might promote ethanol fermentation by regulating genes associated with glucose metabolic process and glycolysis/gluconeogenesis. In addition, KmMsn2 might also help to cope with high temperature by regulating genes associated with lipid metabolism to change the membrane fluidity.The transcription factors KmHsf1 and KmMsn2 of thermotolerant K. marxianus can promote both cell growth and ethanol fermentation of S. cerevisiae at high temperatures. Different mechanisms of KmHsf1 and KmMsn2 in promoting high-temperature ethanol fermentation of S. cerevisiae were revealed by transcriptomic analysis.

Extraction of bioethanol, a potential alternative to fossil fuel in the transport industry, from sweet sorghum stems [Sorghum bicolor (L.) Moench] using solid-state fermentation (SSF) technology has become a popular research topic worldwide. Because SSF technology can directly convert fermentable sugars into target products without juice squeezing and water input, this method can potentially reduce energy and water consumption. However, ethanol extraction from fermented sweet sorghum bagasse requires further investigation. We used batch solid-state distillation to investigate the optimal operating parameters in a distillation column (diameter, 400 mm) via a single-factor experiment. Results showed that the optimal steam flow rate and loading height were 8-10 kg·h−1 and 700-1,000 mm, respectively. Under optimal conditions, an energy consumption of 3.82 tons of steam per ton of ethanol and distillate concentration of 60.9% (v/v) were obtained. The pseudo-first-order rate equation was used to describe the distillation kinetics, and good correlations were obtained. Therefore, solid-state distillation can be effectively used to extract ethanol from fermented sweet sorghum bagasse.

•Photobiological hydrogen driven co-flotation system was established for harvesting of oleaginous microalgae.•Hydrogen production was demonstrated as an essential factor to the system.•The harvests system produces hydrogen and lipid simultaneously.•The co-floated biomass was proved to be an alternative feedstock for biodiesel production.Harvesting of microalgae biomass is recognized as the bottleneck of algal-based biodiesel production due to its high cost and energy input. In this study, an original harvesting system, the co-flotation using the H2 producing filamentous cyanobacterium Anabaena sp. PCC7120 to concentrate the oleaginous alga Chlorella sp., was presented as an alternative strategy. Different mixing ratios of Anabaena and Chlorella were investigated, and 1: 1 (v/v) was shown to be optimal. In the optimal system, each 100 hydrogen producing cells could float 669 Chlorella cells. The lipid of the floating cells was extracted and analyzed by GC-MS. Results suggested that the co-floated algal cells were rich in saturated fatty acids, higher than Chlorella alone, and thus ideal for biodiesel production. Scale up to 1 L experiments demonstrated the system to have the potential for commercial production.

•The relocation of LCC occurred in Ca(OH)2 pretreatment.•Complex formation of LCC and Ca2+ resulted in the relocation.•Lignin did not adsorb cellulase during enzymatic hydrolysis.Sodium hydroxide and calcium hydroxide are used to improve enzymatic hydrolysis of lignocellulose. Compared to NaOH, less carbohydrates was lost in Ca(OH)2 pretreatment. It was found that the substrates with similar lignin content prepared from NaOH and Ca(OH)2 pretreatments had distinct cellulose conversion rate. To understand the mechanism of action, two sweet sorghum bagasse (SSB) samples with similar lignin content were prepared. The enzymatic hydrolysis result showed that the cellulose conversion rate of SSB treated by Ca(OH)2 was about 1.62 times that of SSB treated by NaOH. SEM results showed tiny droplets on the SSB surface pretreated with Ca(OH)2. EDS analysis revealed that the droplets were a complex of lignin–carbohydrate and calcium ions. The results suggested that Ca(OH)2 not only increased the porosity of substrates, but also reduced carbohydrates loss by forming a complex with lignin and calcium ions. This demonstrated that calcium ions could be used to reduce the carbohydrates loss from the pretreatment procedure.

Adsorption of cellulase on substrates is a key step for enzymatic hydrolysis of lignocellulose. Addition of surface active additives affects the interaction between cellulase and substrates and has been proven to enhance enzymatic hydrolysis of lignocellulose by many studies. However, the mechanism of poly(ethylene glycol) effect is not yet clear. In this study, enzymatic activity and the adsorption of cellulase on different substrates with different addition sequence of PEG 4000 were investigated. The crystallinity index of substrates incubated by PEG 4000 was also measured by FTIR and XRD. Except for reduction of unproductive binding of cellulase on lignin which was reported by some literatures, current results confirmed a crucial function of PEG 4000 which prevented cellulase deactivation on cellulose rather than lignin through significant difference in adsorption capacity and enzymatic activity of cellulase with different PEG 4000 addition sequence. This conclusion rationally explained PEG 4000 had positive effect on pure cellulose without lignin as well as on lignocellulosic biomass. In addition, PEG 4000 was also found to be contributed to promote the removal of amorphous cellulose. These conclusions are helpful to understand the effect of surface active additives and optimize the enzymatic hydrolysis process.Graphical abstractHighlights► Different addition sequences of PEG 4000 were adopted to investigate the mechanism of PEG 4000 affected on enzymatic hydrolysis of lignocellulose. ► Compared the adsorption capacity of substrates with different addition sequence of PEG 4000, PEG 4000 was proven to reduce the unproductive adsorption not only on lignin but also on cellulose. ► Cellulase deactivation induced by cellulose was confirmed by decrease of enzymatic activity of cellulase desorbed by PEG 4000. ► Removal of amorphous cellulose promoted by PEG 4000 was confirmed by increase of crystallinity index of substrates treated by PEG 4000.

Corncob is an economic feedstock and more than 20 million tons of corncobs are produced annually in China. Abundant xylose can be potentially converted from the large amount of hemicellulosic materials in corncobs, which makes the crop residue an attractive alternative substrate for a value-added production of a variety of bioproducts. Lactic acid can be used as a precursor for poly-lactic acid production. Although current industrial lactic acid is produced by lactic acid bacteria using enriched medium, production by Rhizopus oryzae is preferred due to its exclusive formation of the l-isomer and a simple nutrition requirement by the fungus. Production of l-(+)-lactic acid by R. oryzae using xylose has been reported; however, its yield and conversion rate are poor compared with that of using glucose. In this study, we report an adapted R. oryzae strain HZS6 that significantly improved efficiency of substrate utilization and enhanced production of l-(+)-lactic acid from corncob hydrolysate. It increased l-(+)-lactic acid final concentration, yield, and volumetric productivity more than twofold compared with its parental strain. The optimized growth and fermentation conditions for Strain HZS6 were defined.

•An integrated process was developed to produce cellulosic ethanol.•Cellulosic ethanol can be cost-effectively produced from SS by using this integrated process.•69.49% theoretical yield of ethanol was achieved under the optimal condition.A cost competitive integrated technology to convert solid state fermented sweet sorghum bagasse (SS) into cellulosic ethanol which combined ethanol distillation, NaOH pretreatment and simultaneous saccharification and co-fermentation (SSCF) was presented in this study. After solid-state fermentation, the SS was distilled with 10% (w/w dry material, DM) NaOH to separate sugar-based ethanol and pretreat lignocelluose simultaneously in one step and one distillation stripper, then the NaOH pretreated SS was subsequently converted into cellulosic ethanol by SSCF. Results showed that 69.49% ethanol theoretical yield was achieved under the optimal condition based on this novel integrated process. This integrated technology can significantly reduce the energy consumption and capital cost for cellulosic ethanol production, and ensure cellulosic ethanol produced from SS cost-effectively.