Bioconversion of lignocellulosic waste to bioethanol by Trichoderma and yeast fermentation

Two new Trichoderma species (Hypocreales, Hypocreaceae) isolated from decaying tubers of Gastrodiaelate

Species of Trichoderma are widely distributed around the world. In this study, two new species in Trichoderma, named as T.albidum and T.variegatum, were introduced and illustrated. These species were isolated from diseased tubers of Gastrodiaelata in China and identified based on morphological characteristics and multi-gene sequence analyses of three loci that is the internal transcribed spacer regions of the ribosomal DNA (ITS), the translation elongation factor 1-α encoding gene (tef1-α) and the gene encoding the second largest nuclear RNA polymerase subunit (rpb2). Distinctions between the new species and their close relatives were discussed. According to results of the phylogenetic analyses, T.albidum belonged to the Harzianum clade and T.variegatum are grouped with species of the Spirale clade. The expansion of two clades provided research foundations for the prevention and control of tuber diseases in G.elata.

Recent Progress and Trends in the Development of Microbial Biofuels from Solid Waste—A Review

This review covers the recent progress in the design and application of microbial biofuels, assessing the advancement of genetic engineering undertakings and their marketability, and lignocellulosic biomass pretreatment issues. Municipal solid waste (MSW) is a promising sustainable biofuel feedstock due to its high content of lignocellulosic fiber. In this review, we compared the production of fatty alcohols, alkanes, and n-butanol from residual biogenic waste and the environmental/economic parameters to that of conventional biofuels. New synthetic biology tools can be used to engineer fermentation pathways within micro-organisms to produce long-chain alcohols, isoprenoids, long-chain fatty acids, and esters, along with alkanes, as substitutes to petroleum-derived fuels. Biotechnological advances have struggled to address problems with bioethanol, such as lower energy density compared to gasoline and high corrosive and hygroscopic qualities that restrict its application in present infrastructure. Biofuels derived from the organic fraction of municipal solid waste (OFMSW) may have less environmental impacts compared to traditional fuel production, with the added benefit of lower production costs. Unfortunately, current advanced biofuel production suffers low production rates, which hinders commercial scaling-up efforts. Microbial-produced biofuels can address low productivity while increasing the spectrum of produced bioenergy molecules.

Bioethanol Production from Cellulose-Rich Corncob Residue by the Thermotolerant Saccharomyces cerevisiae TC-5

This study aimed to select thermotolerant yeast for bioethanol production from cellulose-rich corncob (CRC) residue. An effective yeast strain was identified as Saccharomyces cerevisiae TC-5. Bioethanol production from CRC residue via separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and prehydrolysis-SSF (pre-SSF) using this strain were examined at 35-42 °C compared with the use of commercial S. cerevisiae. Temperatures up to 40 °C did not affect ethanol production by TC-5. The ethanol concentration obtained via the commercial S. cerevisiae decreased with increasing temperatures. The highest bioethanol concentrations obtained via SHF, SSF, and pre-SSF at 35-40 °C of strain TC-5 were not significantly different (20.13-21.64 g/L). The SSF process, with the highest ethanol productivity (0.291 g/L/h), was chosen to study the effect of solid loading at 40 °C. A CRC level of 12.5% (w/v) via fed-batch SSF resulted in the highest ethanol concentrations of 38.23 g/L. Thereafter, bioethanol production via fed-batch SSF with 12.5% (w/v) CRC was performed in 5-L bioreactor. The maximum ethanol concentration and ethanol productivity values were 31.96 g/L and 0.222 g/L/h, respectively. The thermotolerant S. cerevisiae TC-5 is promising yeast for bioethanol production under elevated temperatures via SSF and the use of second-generation substrates.

Bioethanol production from waste lignocelluloses: A review on microbial degradation potential

Tremendous explosion of population has led to about 200% increment of total energy consumptions in last twenty-five years. Apart from conventional fossil fuel as limited energy source, alternative non-conventional sources are being explored worldwide to cater the energy requirement. Lignocellulosic biomass conversion for biofuel production is an important alternative energy source due to its abundance in nature and creating less harmful impacts on the environment in comparison to the coal or petroleum-based sources. However, lignocellulose biopolymer, the building block of plants, is a recalcitrant substance and difficult to break into desirable products. Commonly used chemical and physical methods for pretreating the substrate are having several limitations. Whereas, utilizing microbial potential to hydrolyse the biomass is an interesting area of research. Because of the complexity of substrate, several enzymes are required that can act synergistically to hydrolyse the biopolymer producing components like bioethanol or other energy substances. Exploring a range of microorganisms, like bacteria, fungi, yeast etc. that utilizes lignocelluloses for their energy through enzymatic breaking down the biomass, is one of the options. Scientists are working upon designing organisms through genetic engineering tools to integrate desired enzymes into a single organism (like bacterial cell). Studies on designer cellulosomes and bacteria consortia development relating consolidated bioprocessing are exciting to overcome the issue of appropriate lignocellulose digestions. This review encompasses up to date information on recent developments for effective microbial degradation processes of lignocelluloses for improved utilization to produce biofuel (bioethanol in particular) from the most plentiful substances of our planet.

The Promoter Toolbox for Recombinant Gene Expression in Trichoderma reesei

The ascomycete Trichoderma reesei is one of the main fungal producers of cellulases and xylanases based on its high production capacity. Its enzymes are applied in food, feed, and textile industry or in lignocellulose hydrolysis in biofuel and biorefinery industry. Over the last years, the demand to expand the molecular toolbox for T. reesei to facilitate genetic engineering and improve the production of heterologous proteins grew. An important instrument to modify the expression of key genes are promoters to initiate and control their transcription. To date, the most commonly used promoter for T. reesei is the strong inducible promoter of the main cellobiohydrolase cel7a. Beside this one, there is a number of alternative inducible promoters derived from other cellulase- and xylanase encoding genes and a few constitutive promoters. With the advances in genomics and transcriptomics the identification of new constitutive and tunable promoters with different expression strength was simplified. In this review, we will discuss new developments in the field of promoters and compare their advantages and disadvantages. Synthetic expression systems constitute a new option to control gene expression and build up complex gene circuits. Therefore, we will address common structural features of promoters and describe options for promoter engineering and synthetic design of promoters. The availability of well-characterized gene expression control tools is essential for the analysis of gene function, detection of bottlenecks in gene networks and yield increase for biotechnology applications.

Enzymatic saccharification and fermentation of cellulosic date palm wastes to glucose and lactic acid

The bioconversion of cellulosic wastes into high-value bio-products by saccharification and fermentation processes is an important step that can reduce the environmental pollution caused by agricultural wastes. In this study, enzymatic saccharification of treated and untreated date palm cellulosic wastes by the cellulases from Geobacillus stearothermophilus was optimized. The alkaline pre-treatment of the date palm wastes was found to be effective in increasing the saccharification percentage. The maximum rate of saccharification was found at a substrate concentration of 4% and enzyme concentration of 30 FPU/g of substrate. The optimum pH and temperature for the bioconversions were 5.0 and 50°C, respectively, after 24h of incubation, with a yield of 31.56mg/mL of glucose at a saccharification degree of 71.03%. The saccharification was increased to 94.88% by removal of the hydrolysate after 24h by using a two-step hydrolysis. Significant lactic acid production (27.8mg/mL) was obtained by separate saccharification and fermentation after 72h of incubation. The results indicate that production of fermentable sugar and lactic acid is feasible and may reduce environmental pollution by using date palm wastes as a cheap substrate.