Extremophile-inspired strategies for enzymatic biomass saccharification

Preparation and nutritional properties of xylooligosaccharide from agricultural and forestry byproducts: A comprehensive review

Xylooligosaccharide (XOS) are functional oligosaccharides with prebiotic activities, which originate from lignocellulosic biomass and have attracted extensive attention from scholars in recent years. This paper summarizes the strategies used in the production of XOS, and introduces the raw materials, preparation methods, and purification technology of XOS. In addition, the biological characteristics and applications of XOS are also presented. The most commonly recommended XOS production strategy is the two-stage method of alkaline pre-treatment and enzymatic hydrolysis; and further purification by membrane filtration to achieve the high yield of XOS is required for prebiotic function. At the same time, new strategies and technologies such as the hydrothermal and steam explosion have been used as pre-treatment methods combined with enzymatic hydrolysis to prepare XOS. XOS have many critical physiological activities, especially in regulating blood glucose, reducing blood lipid, and improving the structure of host intestinal flora.

Thermoacidophilic Sulfolobus species as source for extremozymes and as novel archaeal platform organisms

Archaea dominate extreme habitats and possess unique cellular and metabolic properties with novel or modified metabolic pathways and unusual enzymes. Thermoacidophilic Sulfolobus species and their thermo(acido)philic enzymes gained special attention due to their adaptation toward two extremes, high temperature (75-80°C) and low pH (pH 2-5), that matches harsh process conditions in industrial applications. For different Sulfolobus species versatile genetic systems have been established and significant metabolic and physiological information from classical biochemistry and genetic as well as poly-omics and systems biology approaches is available. Their ease of growth under aerobic or microaerophilic conditions and established fermentation technologies gaining high cell yields promote Sulfolobus as source for extremozymes and as valuable novel platform organism for industrial biotechnology.

Optimization of cell culture and cell disruption processes to enhance the production of thermophilic cellulase FnCel5A in E.coli using response surface methodology

FnCel5A from Fervidobacterium nodosum is one of the most thermostable endoglucanases that have phenomenal characteristics, such as high activity, pH stability, and multi-specificity towards various substrates. However, large-scale thermophilic enzyme production is still a challenge. Herein, we focus on an optimization approach based on response surface methodology to improve the production of this enzyme. First, a Box-Behnken design was used to examine physiochemical parameters such as induction temperatures, isopropylβ-D-1-thiogalactopyranoside concentrations and induction times on the heterogeneous expression of FnCel5A gene in E. coli. The best culture was collected after adding 0.56 mM IPTG and incubating it for 29.5 h at 24°C. The highest enzymatic activity observed was 3.31 IU/mL. Second, an economical "thermolysis" cell lysis method for the liberation of the enzymes was also optimized using Box-Behnken design. The optimal levels of the variables were temperature 77°C, pH 7.71, and incubation time of 20 min, which gave about 74.3% higher activity than the well-established bead-milling cell disruption method. The maximum productivity of FnCel5A achieved (5772 IU/L) illustrated that its production increased significantly after combining both optimal models. This strategy can be scaled-up readily for overproduction of FnCel5A from recombinant E.coli to facilitate its usage in biomass energy production.

Optimization of the production of an extracellular and thermostable amylolytic enzyme by Thermus thermophilus HB8 and basic characterization

The objective of this study was to determine the potential of Thermus thermophilus HB8 for accumulating a high level of extracellular, thermostable amylolytic enzyme. Initial production tests indicated clearly that only very low levels of amylolytic activity could be detected, solely from cells after extraction using the mild, non-ionic detergent Triton X-100. A sequential optimization strategy, based on statistical designs, was used to enhance greatly the production of extracellular amylolytic activity to achieve industrially attractive enzyme titers. Focus was placed on the optimal level of initial biomass concentration, culture medium composition and temperature for maximizing extracellular amylolytic enzyme accumulation. Empirical models were then developed describing the effects of the experimental parameters and their interactions on extracellular amylolytic enzyme production. Following such efforts, extracellular amylolytic enzyme accumulation was increased more than 70-fold, with enzyme titers in the 76 U/mL range. The crude extracellular enzyme was thereafter partially characterized. The optimal temperature and pH values were found to be 80 °C and 9.0, respectively. 100% of the initial enzyme activity could be recovered after incubation for 24 h at 80 °C, therefore, proving the very high thermostability of the enzyme preparation.

Membrane Association and Catabolite Repression of the Sulfolobus solfataricus α-Amylase

Sulfolobus solfataricus is a thermoacidophilic member of the archaea whose envelope consists of an ether-linked lipid monolayer surrounded by a protein S-layer. Protein translocation across this envelope must accommodate a steep proton gradient that is subject to temperature extremes. To better understand this process in vivo, studies were conducted on the S. solfataricus glycosyl hydrolyase family 57 α-Amylase (AmyA). Cell lines harboring site specific modifications of the amyA promoter and AmyA structural domains were created by gene replacement using markerless exchange and characterized by Western blot, enzyme assay and culture-based analysis. Fusion of amyA to the malAp promoter overcame amyAp-mediated regulatory responses to media composition including glucose and amino acid repression implicating action act at the level of transcription. Deletion of the AmyA Class II N-terminal signal peptide blocked protein secretion and intracellular protein accumulation. Deletion analysis of a conserved bipartite C-terminal motif consisting of a hydrophobic region followed by several charged residues indicated the charged residues played an essential role in membrane-association but not protein secretion. Mutants lacking the C-terminal bipartite motif exhibited reduced growth rates on starch as the sole carbon and energy source; therefore, association of AmyA with the membrane improves carbohydrate utilization. Widespread occurrence of this motif in other secreted proteins of S. solfataricus and of related Crenarchaeota suggests protein association with membranes is a general trait used by these organisms to influence external processes.

Fluoro-glycosyl acridinones are ultra-sensitive active site titrating agents for retaining β-glycosidases

Novel fluorogenic 2-deoxy-2-fluoroglycosyl acridinone active site titrating reagents were synthesised and kinetic parameters determined for their inactivation of two retaining β-glucosidases, a β-galactosidase, a β-xylosidase and several cellulases. Fluorescence-monitored active site titration using this class of reagents reliably measured active enzyme concentrations down to 3 nM.

Effect of mild alkali pretreatment on structural changes of reed (Phragmites communis Trinius) straw

The effect of dilute sodium hydroxide (NaOH) on reed straw structural change at 105 degreeC temperature was evaluated in this study. Various concentrations of NaOH (1% to 2.5%) were used for pretreatment of reed straw at 105 degreeC for 10min. Scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy studies showed that 2% and 2.5% NaOH pretreated sample exposed more cellulose fibers compared with other treatments. The cellulose crystalline index was increased by the 1% to 2.0% NaOH treatments and slightly lowered by the 2.5% NaOH treatment due to destructing cellulose fibres. Two per cent NaOH pretreatment caused 69.9% lignin removal, whereas 2.5% NaOH pretreatment removed 72.4% lignin. Besides, reed straw, when pretreated at 2% and 2.5% NaOH, resulted 56.4% and 60.5% hemicellulose removal, respectively. However, the difference in removal of lignin and hemicellulose between 2% and 2.5% NaOH treated reed straw was very marginal. In addition, very negligible increase of cellulose level was estimated, amounting 78.8% and 76.6% in 2.5% and 2% NaOH-treated sample, respectively. Moreover, after 72 h, reducing sugar yield was 81.2% and 83.3% using enzyme loading of 15 FPU (g dry biomass)-' and 30 IU (g dry biomass)- and xylanase 4 FXU (g dry biomass)-1 from 2% and 2.5% NaOH pretreated reed straw, respectively. Reducing sugar yield was increased very marginally when NaOH concentration increased from 2% to 2.5% for reed straw pretreatment. Therefore, 2% NaOH is supposed to be effective for reed straw pretreatment at this mentioned condition.

Engineering microbial surfaces to degrade lignocellulosic biomass

Renewable lignocellulosic plant biomass is a promising feedstock from which to produce biofuels, chemicals, and materials. One approach to cost-effectively exploit this resource is to use consolidating bioprocessing (CBP) microbes that directly convert lignocellulose into valuable end products. Because many promising CBP-enabling microbes are non-cellulolytic, recent work has sought to engineer them to display multi-cellulase containing minicellulosomes that hydrolyze biomass more efficiently than isolated enzymes. In this review, we discuss progress in engineering the surfaces of the model microorganisms: Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae. We compare the distinct approaches used to display cellulases and minicellulosomes, as well as their surface enzyme densities and cellulolytic activities. Thus far, minicellulosomes have only been grafted onto the surfaces of B. subtilis and S. cerevisiae, suggesting that the absence of an outer membrane in fungi and Gram-positive bacteria may make their surfaces better suited for displaying the elaborate multi-enzyme complexes needed to efficiently degrade lignocellulose.

Production of total reducing sugar (TRS) from acid hydrolysed potato peels by sonication and its optimization

Potato peel is a waste biomass which can be a source of raw material for biofuel production. This biomass contains a sufficient amount of total reducing sugar (TRS), which can be extracted and further treated with microbial pathways to produce bioethanol. The extraction of TRS from potato peels by hydrolysis in dilute sulphuric acid was investigated at different acid concentrations (0.50%, 0.75% and 1% w/v) and sonication was carried out to improve the extent of sugar extraction after hydrolysis. Response surface methodology based on central composite design was used to verify the experimental data and later applied for the optimization of the main important reaction variables including amplitude (60%, 80% and 100%), cycle (0.6, 0.8 and 1.0) and treatment time (5, 10 and 15 min) for the responses of TRS extraction by acid hydrolysis and later compared with the experimental data.

Recombinant Bacillus subtilis that grows on untreated plant biomass

Lignocellulosic biomass is a promising feedstock to produce biofuels and other valuable biocommodities. A major obstacle to its commercialization is the high cost of degrading biomass into fermentable sugars, which is typically achieved using cellulolytic enzymes from Trichoderma reesei. Here, we explore the use of microbes to break down biomass. Bacillus subtilis was engineered to display a multicellulase-containing minicellulosome. The complex contains a miniscaffoldin protein that is covalently attached to the cell wall and three noncovalently associated cellulase enzymes derived from Clostridium cellulolyticum (Cel48F, Cel9E, and Cel5A). The minicellulosome spontaneously assembles, thus increasing the practicality of the cells. The recombinant bacteria are highly cellulolytic and grew in minimal medium containing industrially relevant forms of biomass as the primary nutrient source (corn stover, hatched straw, and switch grass). Notably, growth did not require dilute acid pretreatment of the biomass and the cells achieved densities approaching those of cells cultured with glucose. An analysis of the sugars released from acid-pretreated corn stover indicates that the cells have stable cellulolytic activity that enables them to break down 62.3% ± 2.6% of the biomass. When supplemented with beta-glucosidase, the cells liberated 21% and 33% of the total available glucose and xylose in the biomass, respectively. As the cells display only three types of enzymes, increasing the number of displayed enzymes should lead to even more potent cellulolytic microbes. This work has important implications for the efficient conversion of lignocellulose to value-added biocommodities.

Comparison of simultaneous and separate processes: saccharification and thermophilic L-lactate fermentation of catch crop and aquatic plant biomass

Catch crop candidates (corn, guinea grass) for recovering nutrients from farm soil and aquatic plants (water caltrop, water hyacinth) were utilized to produce L-lactic acid. The efficiencies ofpre-treatment methods for enzymatic saccharification and L-lactate production of two fermentation processes, thermophilic simultaneous saccharification and fermentation (SSF), as well as separate saccharification and fermentation, were compared. Conditions were set at 55 degrees C and pH 5.5 for non-sterile fermentation. Alkaline/peroxide pre-treatment proved the most effective for saccharification in pre-treated corn, guinea grass, water caltrop and water hyacinth with glucose yields of 0.23, 0.20, 0.11 and 0.14 g/g-dry native biomass (24-hour incubation period), respectively. Examination of the two types of thermophilic L-lactate fermentation employed following alkaline/peroxide pre-treatment and saccharification demonstrated that the L-lactate yield obtained using SSF (0.15 g/g in the case of corn) was lower than that obtained using separate saccharification and fermentation (0.28 g/g in the case of corn). The lower yield obtained from SSF is likely to have resulted from the saccharification conditions used in the present study, as the possibility of cellulase deactivation during SSF by thermophilic L-lactate producing bacteria existed. A cellulase that retains high activity levels under non-sterile conditions and a L-lactate producer without cellulose hydrolysis activity would be required in order for SSF to serve as an effective method of L-lactate production.

Engineering thermoacidophilic archaea using linear DNA recombination

Thermoacidophilic archaea comprise one of the major classes of extremophiles. Most belong to the family Sulfolobales within the phylum Crenarchaeota. They are of applied interest as sources of hyperstable enzymes, for biomining of base and precious metals, and for evolutionary studies because of their use of eukaryotic-like subcellular mechanisms. Genetic methods are available for several species particularly Sulfolobus solfataricus. This organism has a considerable number of methods available for the construction of novel cell lines with unique functions. This chapter presents recent developments in the use of homologous recombination and linear DNA for the engineering of site-specific changes in the genome of S. solfataricus.

Assembly of minicellulosomes on the surface of Bacillus subtilis

To cost-efficiently produce biofuels, new methods are needed to convert lignocellulosic biomass into fermentable sugars. One promising approach is to degrade biomass using cellulosomes, which are surface-displayed multicellulase-containing complexes present in cellulolytic Clostridium and Ruminococcus species. In this study we created cellulolytic strains of Bacillus subtilis that display one or more cellulase enzymes. Proteins containing the appropriate cell wall sorting signal are covalently anchored to the peptidoglycan by coexpressing them with the Bacillus anthracis sortase A (SrtA) transpeptidase. This approach was used to covalently attach the Cel8A endoglucanase from Clostridium thermocellum to the cell wall. In addition, a Cel8A-dockerin fusion protein was anchored on the surface of B. subtilis via noncovalent interactions with a cell wall-attached cohesin module. We also demonstrate that it is possible to assemble multienzyme complexes on the cell surface. A three-enzyme-containing minicellulosome was displayed on the cell surface; it consisted of a cell wall-attached scaffoldin protein noncovalently bound to three cellulase-dockerin fusion proteins that were produced in Escherichia coli. B. subtilis has a robust genetic system and is currently used in a wide range of industrial processes. Thus, grafting larger, more elaborate minicellulosomes onto the surface of B. subtilis may yield cellulolytic bacteria with increased potency that can be used to degrade biomass.

Enzymatic and whole cell catalysis: finding new strategies for old processes

The use of enzymes and whole bacterial cells has allowed the production of a plethora of compounds that have been used for centuries in foods and beverages. However, only recently we have been able to master techniques that allow the design and development of new biocatalysts with high stability and productivity. Rational redesign and directed evolution have lead to engineered enzymes with new characteristics whilst the understanding of adaptation mechanisms in bacterial cells has allowed their use under new operational conditions. Bacteria able to thrive under the most extreme conditions have also provided new and extraordinary catalytic processes. In this review, the new tools available for the improvement of biocatalysts are presented and discussed.