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      Bioethanol production using vegetable peels medium and the effective role of cellulolytic bacterial (Bacillus subtilis) pre-treatment

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          Abstract

          Background:  The requirement of an alternative clean energy source is increasing with the elevating energy demand of modern age. Bioethanol is considered as an excellent candidate to satiate this demand.

          Methods: Yeast isolates were used for the production of bioethanol using cellulosic vegetable wastes as substrate. Efficient bioconversion of lignocellulosic biomass into ethanol was achieved by the action of cellulolytic bacteria ( Bacillus subtilis).  After proper isolation, identification and characterization of stress tolerances (thermo-, ethanol-, pH-, osmo- & sugar tolerance), optimization of physiochemical parameters for ethanol production by the yeast isolates was assessed. Very inexpensive and easily available raw materials (vegetable peels) were used as fermentation media. Fermentation was optimized with respect to temperature, reducing sugar concentration and pH.

          Results: It was observed that temperatures of 30°C and pH 6.0 were optimum for fermentation with a maximum yield of ethanol. The results indicated an overall increase in yields upon the pretreatment of Bacillus subtilis; maximum ethanol percentages for isolate SC1 obtained after 48-hour incubation under pretreated substrate was 14.17% in contrast to untreated media which yielded 6.21% after the same period. Isolate with the highest ethanol production capability was identified as members of the ethanol-producing Saccharomyces species after stress tolerance studies and biochemical characterization using Analytical Profile Index (API) ® 20C AUX and nitrate broth test. Introduction of Bacillus subtilis increased the alcohol production rate from the fermentation of cellulosic materials.

          Conclusions: The study suggested that the kitchen waste can serve as a raw material in ethanol fermentation.

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          Substrate pretreatment: the key to effective enzymatic hydrolysis of lignocellulosics?

          Although the structure and function of cellulase systems continue to be the subject of intense research, it is widely acknowledged that the rate and extent of the cellulolytic hydrolysis of lignocellulosic substrates is influenced not only by the effectiveness of the enzymes but also by the chemical, physical and morphological characteristics of the heterogeneous lignocellulosic substrates. Although strategies such as site-directed mutagenesis or directed evolution have been successfully employed to improve cellulase properties such as binding affinity, catalytic activity and thermostability, complementary goals that we and other groups have studied have been the determination of which substrate characteristics are responsible for limiting hydrolysis and the development of pretreatment methods that maximize substrate accessibility to the cellulase complex. Over the last few years we have looked at the various lignocellulosic substrate characteristics at the fiber, fibril and microfibril level that have been modified during pretreatment and subsequent hydrolysis. The initial characteristics of the woody biomass and the effect of subsequent pretreatment play a significant role on the development of substrate properties, which in turn govern the efficacy of enzymatic hydrolysis. Focusing particularly on steam pretreatment, this review examines the influence that pretreatment conditions have on substrate characteristics such as lignin and hemicellulose content, crystallinity, degree of polymerization and specific surface, and the resulting implications for effective hydrolysis by cellulases.
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            Hybridization and adaptive evolution of diverse Saccharomyces species for cellulosic biofuel production

            Background Lignocellulosic biomass is a common resource across the globe, and its fermentation offers a promising option for generating renewable liquid transportation fuels. The deconstruction of lignocellulosic biomass releases sugars that can be fermented by microbes, but these processes also produce fermentation inhibitors, such as aromatic acids and aldehydes. Several research projects have investigated lignocellulosic biomass fermentation by the baker’s yeast Saccharomyces cerevisiae. Most projects have taken synthetic biological approaches or have explored naturally occurring diversity in S. cerevisiae to enhance stress tolerance, xylose consumption, or ethanol production. Despite these efforts, improved strains with new properties are needed. In other industrial processes, such as wine and beer fermentation, interspecies hybrids have combined important traits from multiple species, suggesting that interspecies hybridization may also offer potential for biofuel research. Results To investigate the efficacy of this approach for traits relevant to lignocellulosic biofuel production, we generated synthetic hybrids by crossing engineered xylose-fermenting strains of S. cerevisiae with wild strains from various Saccharomyces species. These interspecies hybrids retained important parental traits, such as xylose consumption and stress tolerance, while displaying intermediate kinetic parameters and, in some cases, heterosis (hybrid vigor). Next, we exposed them to adaptive evolution in ammonia fiber expansion-pretreated corn stover hydrolysate and recovered strains with improved fermentative traits. Genome sequencing showed that the genomes of these evolved synthetic hybrids underwent rearrangements, duplications, and deletions. To determine whether the genus Saccharomyces contains additional untapped potential, we screened a genetically diverse collection of more than 500 wild, non-engineered Saccharomyces isolates and uncovered a wide range of capabilities for traits relevant to cellulosic biofuel production. Notably, Saccharomyces mikatae strains have high innate tolerance to hydrolysate toxins, while some Saccharomyces species have a robust native capacity to consume xylose. Conclusions This research demonstrates that hybridization is a viable method to combine industrially relevant traits from diverse yeast species and that members of the genus Saccharomyces beyond S. cerevisiae may offer advantageous genes and traits of interest to the lignocellulosic biofuel industry. Electronic supplementary material The online version of this article (doi:10.1186/s13068-017-0763-7) contains supplementary material, which is available to authorized users.
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              A Review of Bioethanol Production from Plant-based Waste Biomass by Yeast Fermentation

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                Author and article information

                Contributors
                Role: Data CurationRole: Formal AnalysisRole: Investigation
                Role: Data CurationRole: Formal AnalysisRole: Investigation
                Role: ValidationRole: VisualizationRole: Writing – Original Draft PreparationRole: Writing – Review & Editing
                Role: ConceptualizationRole: Funding AcquisitionRole: MethodologyRole: Project AdministrationRole: ResourcesRole: Supervision
                Role: ConceptualizationRole: MethodologyRole: Project AdministrationRole: Supervision
                Journal
                F1000Res
                F1000Res
                F1000Research
                F1000Research
                F1000 Research Limited (London, UK )
                2046-1402
                3 May 2018
                2018
                : 7
                : 271
                Affiliations
                [1 ]Department of Mathematics and Natural Sciences, BRAC University, Dhaka, 1212, Bangladesh
                [2 ]United Surgical (BD) Ltd, Kadda, Gazipur, 1702, Bangladesh
                [3 ]Bangladesh Atomic Energy Regulatory Authority (BAERA), Dhaka, 1207, Bangladesh
                [1 ]Department of Molecular Physiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan
                [1 ]Faculty of Integrated Technologies (FIT), University of Brunei Darussalam, Gadong, Brunei
                [1 ]Department of Molecular Physiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan
                United Surgical (BD) Ltd., Bangladesh
                [1 ]Faculty of Integrated Technologies (FIT), University of Brunei Darussalam, Gadong, Brunei
                United Surgical (BD) Ltd., Bangladesh
                Author notes

                These authors contributed equally

                No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Competing interests: No competing interests were disclosed.

                Author information
                https://orcid.org/0000-0002-9813-1548
                Article
                10.12688/f1000research.13952.2
                5968363
                29899975
                2a0249ec-d5fb-4dda-b848-9e9b9200dba9
                Copyright: © 2018 Promon SK et al.

                This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 2 May 2018
                Funding
                Funded by: Ministry of Science and Technology, Government of the People’s Republic of Bangladesh
                Award ID: 39.009.002.01.000.053.2014-2015/16/BS-31
                This study was conducted under a grant (39.009.002.01.000.053.2014-2015/16/BS-31) of Ministry of Science and Technology (Government of Bangladesh).
                The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Articles

                bioethanol,yeast,cellulolytic bacteria
                bioethanol, yeast, cellulolytic bacteria

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