Grass cell wall properties influence food, feed, and biofuel feedstock usage efficiency. The glucuronoarabinoxylan of grass cell walls is esterified with the phenylpropanoid-derived hydroxycinnamic acids ferulic acid (FA) and para-coumaric acid (p-CA). Feruloyl esters undergo oxidative coupling with neighboring phenylpropanoids on glucuronoarabinoxylan and lignin. Examination of rice (Oryza sativa) mutants in a grass-expanded and -diverged clade of BAHD acyl-coenzyme A-utilizing transferases identified four mutants with altered cell wall FA or p-CA contents. Here, we report on the effects of overexpressing one of these genes, OsAt10 (LOC_Os06g39390), in rice. An activation-tagged line, OsAT10-D1, shows a 60% reduction in matrix polysaccharide-bound FA and an approximately 300% increase in p-CA in young leaf tissue but no discernible phenotypic alterations in vegetative development, lignin content, or lignin composition. Two additional independent OsAt10 overexpression lines show similar changes in FA and p-CA content. Cell wall fractionation and liquid chromatography-mass spectrometry experiments isolate the cell wall alterations in the mutant to ester conjugates of a fivecarbon sugar with p-CA and FA. These results suggest that OsAT10 is a p-coumaroyl coenzyme A transferase involved in glucuronoarabinoxylan modification. Biomass from OsAT10-D1 exhibits a 20% to 40% increase in saccharification yield depending on the assay. Thus, OsAt10 is an attractive target for improving grass cell wall quality for fuel and animal feed.

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A novel Shigella strain (Shigella flexneri G3) showing high cellulolytic activity under mesophilic, anaerobic conditions was isolated and characterized. The bacterium is Gram negative, short rod shaped, and nonmotile and displays effective production of glucose, cellobiose, and other oligosaccharides from cellulose (Avicel PH-101) under optimal conditions (40°C and pH 6.5). Approximately 75% of the cellulose was hydrolyzed in modified ATCC 1191 medium containing 0.3% cellulose, and the oligosaccharide production yield and specific production rate reached 375 mg g Avicel ؊1 and 6.25 mg g Avicel ؊1 h ؊1 , respectively, after a 60-hour incubation. To our knowledge, this represents the highest oligosaccharide yield and specific rate from cellulose for mesophilic bacterial monocultures reported so far. The results demonstrate that S. flexneri G3 is capable of rapid conversion of cellulose to oligosaccharides, with potential biofuel applications under mesophilic conditions.Lignocellulosic biomass is abundant in nature, as well as in agricultural, forestry, and municipal wastes, and can be used as an excellent bioconversion feedstock. Biomass-derived saccharides, such as glucose, cellobiose, and other minor sugars, can be readily fermented by appropriate microbes into bioenergy products, such as hydrogen, ethanol, biodiesel, and other commodity chemicals. However, the high cost of converting biomass to sugars is the primary factor impeding establishment of a cellulosic-biofuels industry (24, 40). Lignocellulosic biofuels can be competitive on an industrial scale if efficient technologies can be developed (29,39). Currently, the most efficient process for utilization of cellulose as a feed stock is either a three-step process (separate hydrolysis and fermentation [SHF]) involving separate pretreatment, cellulose hydrolysis (i.e., saccharification), and hexose and pentose fermentation steps or a two-step process (simultaneous saccharification and fermentation [SSF]) involving separate pretreatment and simultaneous saccharification of hexose and pentose fermentation (48, 64). Combining hydrolysis of cellulose with simultaneous fermentation of hexose and pentose in a single process, i.e., direct microbial conversion (DMC), is an ideal strategy for converting cellulosic biomass to ethanol. However, no single microorganism/community can implement DMC with high efficiency (67). In any of these configurations, rapid and efficient saccharification is critical for developing competitive biotechnologies for cellulosic-biofuel production.In nature, cellulose is hydrolyzed to oligosaccharides by microorganisms, mainly fungi (e.g., brown-, white-, and soft-rot fungi) and bacteria (e.g., Clostridium and Cellulomonas), which produce either free cellulolytic enzymes or extracellular enzyme complexes known as cellulosomes (12). Many white-rot Basidiomycetes and some Actinomycetes have been employed for hydrolyzing lignocellulosic materials. For example, Trichoderma reesei has shown the highest cellulolytic activity currently known (27)....

BackgroundLignocellulosic biomass is one of earth’s most abundant resources, and it has great potential for biofuel production because it is renewable and has carbon-neutral characteristics. Lignocellulose is mainly composed of carbohydrate polymers (cellulose and hemicellulose), which contain approximately 75 % fermentable sugars for biofuel fermentation. However, saccharification by cellulases is always the main bottleneck for commercialization. Compared with the enzyme systems of fungi, bacteria have evolved distinct systems to directly degrade lignocellulose. However, most reported bacterial saccharification is not efficient enough without help from additional β-glucosidases. Thus, to enhance the economic feasibility of using lignocellulosic biomass for biofuel production, it will be extremely important to develop a novel bacterial saccharification system that does not require the addition of β-glucosidases.ResultsIn this study, a new thermophilic bacterium named Ruminiclostridium thermocellum M3, which could directly saccharify lignocellulosic biomass, was isolated from horse manure. The results showed that R. thermocellum M3 can grow at 60 °C on a variety of carbon polymers, including microcrystalline cellulose, filter paper, and xylan. Upon utilization of these substrates, R. thermocellum M3 achieved an oligosaccharide yield of 481.5 ± 16.0 mg/g Avicel, and a cellular β-glucosidase activity of up to 0.38 U/mL, which is accompanied by a high proportion (approximately 97 %) of glucose during the saccharification. R. thermocellum M3 also showed potential in degrading natural lignocellulosic biomass, without additional pretreatment, to oligosaccharides, and the oligosaccharide yields using poplar sawdust, corn cobs, rice straw, and cornstalks were 52.7 ± 2.77, 77.8 ± 5.9, 89.4 ± 9.3, and 107.8 ± 5.88 mg/g, respectively.ConclusionsThe newly isolated strain R. thermocellum M3 degraded lignocellulose and accumulated oligosaccharides. R. thermocellum M3 saccharified lignocellulosic feedstock without the need to add β-glucosidases or control the pH, and the high proportion of glucose production distinguishes it from all other known monocultures of cellulolytic bacteria. R. thermocellum M3 is a potential candidate for lignocellulose saccharification, and it is a valuable choice for the refinement of bioproducts.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0585-z) contains supplementary material, which is available to authorized users.