Microbial interactions during sugar cane must fermentation for bioethanol production: does quorum sensing play a role?

Microbial interactions represent important modulatory role in the dynamics of biological processes. During bioethanol production from sugar cane must, the presence of lactic acid bacteria (LAB) and wild yeasts is inevitable as they originate from the raw material and industrial environment. Increasing the concentration of ethanol, organic acids, and other extracellular metabolites in the fermentation must are revealed as wise strategies for survival by certain microorganisms. Despite this, the co-existence of LAB and yeasts in the fermentation vat and production of compounds such as organic acids and other extracellular metabolites result in reduction in the final yield of the bioethanol production process. In addition to the competition for nutrients, reduction of cellular viability of yeast strain responsible for fermentation, flocculation, biofilm formation, and changes in cell morphology are listed as important factors for reductions in productivity. Although these consequences are scientifically well established, there is still a gap about the physiological and molecular mechanisms governing these interactions. This review aims to discuss the potential occurrence of quorum sensing mechanisms between bacteria (mainly LAB) and yeasts and to highlight how the understanding of such mechanisms can result in very relevant and useful tools to benefit the biofuels industry and other sectors of biotechnology in which bacteria and yeast may co-exist in fermentation processes.     

A simple and effective set of PCR-based molecular markers for the monitoring of the Saccharomyces cerevisiae cell population during bioethanol fermentation

One of the defining features of the fermentation process used in the production of bioethanol from sugarcane feedstock is the dynamic nature of the yeast population. Minisatellite molecular markers are particularly useful for monitoring yeast communities because they produce polymorphic PCR products that typically display wide size variations. We compared the coding sequences derived from the genome of the sugarcane bioethanol strain JAY270/PE-2 to those of the reference Saccharomyces cerevisiae laboratory strain S288c, and searched for genes containing insertion or deletion polymorphisms larger than 24 bp. We then designed oligonucleotide primers flanking nine of these sites, and used them to amplify differentially sized PCR products. We analyzed the banding patterns in the most widely adopted sugarcane bioethanol strains and in several indigenous yeast contaminants, and found that our marker set had very good discriminatory power. Subsequently, these markers were used to successfully monitor the yeast cell populations in six sugarcane bioethanol distilleries. Additionally, we showed that most of the markers described here are also polymorphic among strains unrelated to bioethanol production, suggesting that they may be applied universally in S. cerevisiae. Because the relatively large polymorphisms are detectable in conventional agarose gels, our method is well suited to modestly equipped on-site laboratories at bioethanol distilleries, therefore providing both cost and time savings.     

Genetic improvement of Saccharomyces cerevisiae for xylose fermentation

There is considerable interest in recent years in the bioconversion of forestry and agricultural residues into ethanol and value-added chemicals. High ethanol yields from lignocellulosic residues are dependent on efficient use of all the available sugars including glucose and xylose. The well-known fermentative yeast Saccharomyces cerevisiae is the preferred microorganism for ethanol production, but unfortunately, this yeast is unable to ferment xylose. Over the last 15 years, this yeast has been the subject of various research efforts aimed at improving its ability to utilize xylose and ferment it to ethanol. This review examines the research on S. cerevisiae strains that have been genetically modified or adapted to ferment xylose to ethanol. The current state of these efforts and areas where further research is required are identified and discussed.     

Cellulase immobilized magnetic nanoparticles for green energy production from Allamanda schottii L: Sustainability research in waste recycling

This study presents ethanol''s fabrication by fermenting the golden trumpet flower (Allamanda schottii L) with the yeast strain Saccharomyces cerevisiae. The changes in different parameters during fermentation were studied and optimized while producing the ethanol and the end product was subjected to emission test study by blending petrol and ethanol. The Allamanda floral substrate contains 65% polysaccharides. The strain S. cerevisiae was obtained in the form of baker’s yeast from a domestic shop. For 100 ml of slurry, the highest bioethanol yield recorded was about 18.75 ml via optimization of different culture conditions, including a 1:8 ratio for slurry preparation, maintained under 35 ⁰C, 5.5 pH, 72 h. old inoculum with a quantity of 3.75 g 100 ml⁻¹, fermented for120 h. The highest yield of bioethanol was acquired under the addition of urea. This technique & design is capable of industrial-scale fabrication of bioethanol by using A. schottii floral substrates. This research was conducted to fabricate ethanol by fermentation (A. schottii L) floral substrate with S. cerevisiae. The optimum physiochemical parameters required to obtain the highest yield of bioethanol from A. schottii flower by fermentation was studied. The immobilization strategy with a cheap agricultural substrate and magnetic nanoparticles were also studied. The engine performance and emission studies were done with different blends of petrol and bio-ethanol.     

Production of bioethanol, methane and heat from sugarcane bagasse in a biorefinery concept

The potential of biogas production from the residues of second generation bioethanol production was investigated taking into consideration two types of pretreatment: lime or alkaline hydrogen peroxide. Bagasse was pretreated, enzymatically hydrolyzed and the wastes from pretreatment and hydrolysis were used to produce biogas. Results have shown that if pretreatment is carried out at a bagasse concentration of 4% DM, the highest global methane production is obtained with the peroxide pretreatment: 72.1 L methane/kg bagasse. The recovery of lignin from the peroxide pretreatment liquor was also the highest, 112.7 ± 0.01 g/kg of bagasse. Evaluation of four different biofuel production scenarios has shown that 63-65% of the energy that would be produced by bagasse incineration can be recovered by combining ethanol production with the combustion of lignin and hydrolysis residues, along with the anaerobic digestion of pretreatment liquors, while only 32-33% of the energy is recovered by bioethanol production alone.     

Optimization of H2SO4-catalyzed hydrothermal pretreatment of rapeseed straw for bioconversion to ethanol: Focusing on pretreatment at high solids content

A central composite design of response surface method was used to optimize H₂SO₄-catalyzed hydrothermal pretreatment of rapeseed straw, in respect to acid concentration (0.5–2%), treatment time (5–20 min) and solid content (10–20%) at 180 °C. Enzymatic hydrolysis and fermentation were also measured to evaluate the optimal pretreatment conditions for maximizing ethanol production. The results showed that acid concentration and treatment time were more significant than solid content for optimization of xylose release and cellulose recovery. Pretreatment with 1% sulfuric acid and 20% solid content for 10 min at 180 °C was found to be the most optimal condition for pretreatment of rapeseed straw for ethanol production. After pretreatment at the optimal condition and enzymatic hydrolysis, 75.12% total xylan and 63.17% total glucan were converted to xylose and glucose, respectively. Finally, 66.79% of theoretical ethanol yielded after fermentation.     

Key technologies for bioethanol production from lignocellulose

Controversies on bioethanol produced from straw mainly revolve around the unfitted economical feasibility and environmental concerns of the process, which attribute mainly to unilateral researches from own specialties of each scholar without regard to the characteristics of the straws themselves. To achieve an economical and environmentally-friendly system of bioethanol production from straw, a number of breakthroughs are needed, not only in individual process steps, but also in the balance and combination of these processes. This article gives an overview of the new technologies required and the advances achieved in recent years, especial progresses achieved in our group, based on the concept of fractional conversions. An eco-industrial multi-production pattern is established, by which the maximum efficacy and benefit of process can be achieved due to the production of many high-value co-products simultaneously with ethanol. We believed that, in the future, the bioethanol production from straw will be competitive economically and environmentally.     

Mild alkaline pretreatment can achieve high hydrolytic and fermentation efficiencies for rice straw conversion to bioethanol

Abstract

Mild alkaline pretreatment was evaluated as a strategy for effective lignin removal and hydrolysis of rice straw. The pretreatment efficiency of different NaOH concentrations (0.5, 1.0, 1.5 or 2.0% w/w) was assessed. Rice straw (RS) pretreated with 1.5% NaOH achieved better sugar yield compared to other concentrations used. A cellulose conversion efficiency of 91% (45.84?mg/ml glucose release) was attained from 1.5% NaOH pretreated rice straw (PRS), whereas 1% NaOH pretreated rice straw yielded 35.10?mg/ml of glucose corresponding to a cellulose conversion efficiency of 73.81%. The ethanol production from 1% and 1.5% NaOH pretreated RS hydrolysates was similar at ～3.3% (w/v), corresponding to a fermentation efficiency of 86%. The non-detoxified hydrolysate was fermented using the novel yeast strain Saccharomyces cerevisiae RPP-03O without any additional supplementation of nutrients.     

Simultaneous secretion of seven lignocellulolytic enzymes by an industrial second-generation yeast strain enables efficient ethanol production from multiple polymeric substrates

A major hurdle in the production of bioethanol with second-generation feedstocks is the high cost of the enzymes for saccharification of the lignocellulosic biomass into fermentable sugars. Simultaneous saccharification and fermentation with Saccharomyces cerevisiae yeast that secretes a range of lignocellulolytic enzymes might address this problem, ideally leading to consolidated bioprocessing. However, it has been unclear how many enzymes can be secreted simultaneously and what the consequences would be on the C6 and C5 sugar fermentation performance and robustness of the second-generation yeast strain. We have successfully expressed seven secreted lignocellulolytic enzymes, namely endoglucanase, β-glucosidase, cellobiohydrolase I and II, xylanase, β-xylosidase and acetylxylan esterase, in a single second-generation industrial S. cerevisiae strain, reaching 94.5 FPU/g CDW and enabling direct conversion of lignocellulosic substrates into ethanol without preceding enzyme treatment. Neither glucose nor the engineered xylose fermentation were significantly affected by the heterologous enzyme secretion. This strain can therefore serve as a promising industrial platform strain for development of yeast cell factories that can significantly reduce the enzyme cost for saccharification of lignocellulosic feedstocks.