Abstract:Because cellulosic ethanol production remains cost‐prohibitive„ advances in consolidated bioprocessing (CBP) have been directed towards lifting this restriction. CBP reduces the need for added enzymes and can potentially slash ethanol production costs through process integration. Clostridium thermocellum, a CBP microorganism, organizes its enzymes in a multi‐enzyme complex ‐ a stark contrast to fungal enzymes. Nonetheless, recalcitrance may limit the extent of biomass deconstruction. Herein, six Populus were t… Show more
“…S5A). The CBI reference poplar line (GW-9947) was previously identified as a low recalcitrance poplar natural variant with reduced lignin and a high syringyl-to-guaiacyl (S/G) ratio [ 18 ], a difference confirmed by the py-MBMS lignin analysis results reported here. Fig.…”
Section: Resultssupporting
confidence: 69%
“…4 E). A higher S/G ratio in the residual solids following C. thermocellum CBP fermentation of poplar wood has been previously described [ 16 , 18 – 20 ]. One hypothesis for explaining this result is that some of the hemicellulose or cellulose solubilized by C. thermocellum is associated with lignin that has a higher G/S ratio, which was preferentially solubilized along with the glycans.…”
Section: Resultsmentioning
confidence: 99%
“…However, without pretreatment of the lignocellulosic biomass, this cellulolytic microbe cannot completely depolymerize the native complex polysaccharides in the plant cell wall of either woody and mature grassy feedstocks. The objective of this study was to characterize the solubilization of both cellulose and non-cellulosic sugars from non-pretreated milled CBI reference poplar biomass [ 18 ] by C. thermocellum by evaluating the starting biomass, the post-fermentation liquors, and solid residues recovered during the CBP process. Our goal was to quantify the amount of cellulosic and non-cellulosic sugars solubilized during the CBP process to provide information about which polymers in woody biomass C. thermocellum solubilizes and to identify potential limiting factors that could inform the development of an economically viable consolidated bioprocess.…”
Section: Discussionmentioning
confidence: 99%
“…The goal of this study was to better understand the solubilization of cellulose and non-cellulosic sugars from milled, non-pretreated Center for Bioenergy Innovation (CBI) reference poplar [ 18 ] during CBP by C. thermocellum DSM1313. Determination of cellulosic and non-cellulosic sugar mass yields in both the fermentation broth and solid residues during CBP by C. thermocellum was carried out to identify potential cell wall structural and architectural changes and limitations to solubilization of non-pretreated poplar biomass.…”
Background
Terrestrial plant biomass is the primary renewable carbon feedstock for enabling transition to a sustainable bioeconomy. Consolidated bioprocessing (CBP) by the cellulolytic thermophile Clostridium thermocellum offers a single step microbial platform for production of biofuels and biochemicals via simultaneous solubilization of carbohydrates from lignocellulosic biomass and conversion to products. Here, solubilization of cell wall cellulosic, hemicellulosic, and pectic polysaccharides in the liquor and solid residues generated during CBP of poplar biomass by C. thermocellum was analyzed.
Results
The total amount of biomass solubilized in the C. thermocellum DSM1313 fermentation platform was 5.8, 10.3, and 13.7% of milled non-pretreated poplar after 24, 48, and 120 h, respectively. These results demonstrate solubilization of 24% cellulose and 17% non-cellulosic sugars after 120 h, consistent with prior reports. The net solubilization of non-cellulosic sugars by C. thermocellum (after correcting for the uninoculated control fermentations) was 13 to 36% of arabinose (Ara), xylose (Xyl), galactose (Gal), mannose (Man), and glucose (Glc); and 15% and 3% of fucose and glucuronic acid, respectively. No rhamnose was solubilized and 71% of the galacturonic acid (GalA) was solubilized. These results indicate that C. thermocellum may be selective for the types and/or rate of solubilization of the non-cellulosic wall polymers. Xyl, Man, and Glc were found to accumulate in the fermentation liquor at levels greater than in uninoculated control fermentations, whereas Ara and Gal did not accumulate, suggesting that C. thermocellum solubilizes both hemicelluloses and pectins but utilizes them differently. After five days of fermentation, the relative amount of Rha in the solid residues increased 21% indicating that the Rha-containing polymer rhamnogalacturonan I (RG-I) was not effectively solubilized by C. thermocellum CBP, a result confirmed by immunoassays. Comparison of the sugars in the liquor versus solid residue showed that C. thermocellum solubilized hemicellulosic xylan and mannan, but did not fully utilize them, solubilized and appeared to utilize pectic homogalacturonan, and did not solubilize RG-I.
Conclusions
The significant relative increase in RG-I in poplar solid residues following CBP indicates that C. thermocellum did not solubilize RG-I. These results support the hypothesis that this pectic glycan may be one barrier for efficient solubilization of poplar by C. thermocellum.
“…S5A). The CBI reference poplar line (GW-9947) was previously identified as a low recalcitrance poplar natural variant with reduced lignin and a high syringyl-to-guaiacyl (S/G) ratio [ 18 ], a difference confirmed by the py-MBMS lignin analysis results reported here. Fig.…”
Section: Resultssupporting
confidence: 69%
“…4 E). A higher S/G ratio in the residual solids following C. thermocellum CBP fermentation of poplar wood has been previously described [ 16 , 18 – 20 ]. One hypothesis for explaining this result is that some of the hemicellulose or cellulose solubilized by C. thermocellum is associated with lignin that has a higher G/S ratio, which was preferentially solubilized along with the glycans.…”
Section: Resultsmentioning
confidence: 99%
“…However, without pretreatment of the lignocellulosic biomass, this cellulolytic microbe cannot completely depolymerize the native complex polysaccharides in the plant cell wall of either woody and mature grassy feedstocks. The objective of this study was to characterize the solubilization of both cellulose and non-cellulosic sugars from non-pretreated milled CBI reference poplar biomass [ 18 ] by C. thermocellum by evaluating the starting biomass, the post-fermentation liquors, and solid residues recovered during the CBP process. Our goal was to quantify the amount of cellulosic and non-cellulosic sugars solubilized during the CBP process to provide information about which polymers in woody biomass C. thermocellum solubilizes and to identify potential limiting factors that could inform the development of an economically viable consolidated bioprocess.…”
Section: Discussionmentioning
confidence: 99%
“…The goal of this study was to better understand the solubilization of cellulose and non-cellulosic sugars from milled, non-pretreated Center for Bioenergy Innovation (CBI) reference poplar [ 18 ] during CBP by C. thermocellum DSM1313. Determination of cellulosic and non-cellulosic sugar mass yields in both the fermentation broth and solid residues during CBP by C. thermocellum was carried out to identify potential cell wall structural and architectural changes and limitations to solubilization of non-pretreated poplar biomass.…”
Background
Terrestrial plant biomass is the primary renewable carbon feedstock for enabling transition to a sustainable bioeconomy. Consolidated bioprocessing (CBP) by the cellulolytic thermophile Clostridium thermocellum offers a single step microbial platform for production of biofuels and biochemicals via simultaneous solubilization of carbohydrates from lignocellulosic biomass and conversion to products. Here, solubilization of cell wall cellulosic, hemicellulosic, and pectic polysaccharides in the liquor and solid residues generated during CBP of poplar biomass by C. thermocellum was analyzed.
Results
The total amount of biomass solubilized in the C. thermocellum DSM1313 fermentation platform was 5.8, 10.3, and 13.7% of milled non-pretreated poplar after 24, 48, and 120 h, respectively. These results demonstrate solubilization of 24% cellulose and 17% non-cellulosic sugars after 120 h, consistent with prior reports. The net solubilization of non-cellulosic sugars by C. thermocellum (after correcting for the uninoculated control fermentations) was 13 to 36% of arabinose (Ara), xylose (Xyl), galactose (Gal), mannose (Man), and glucose (Glc); and 15% and 3% of fucose and glucuronic acid, respectively. No rhamnose was solubilized and 71% of the galacturonic acid (GalA) was solubilized. These results indicate that C. thermocellum may be selective for the types and/or rate of solubilization of the non-cellulosic wall polymers. Xyl, Man, and Glc were found to accumulate in the fermentation liquor at levels greater than in uninoculated control fermentations, whereas Ara and Gal did not accumulate, suggesting that C. thermocellum solubilizes both hemicelluloses and pectins but utilizes them differently. After five days of fermentation, the relative amount of Rha in the solid residues increased 21% indicating that the Rha-containing polymer rhamnogalacturonan I (RG-I) was not effectively solubilized by C. thermocellum CBP, a result confirmed by immunoassays. Comparison of the sugars in the liquor versus solid residue showed that C. thermocellum solubilized hemicellulosic xylan and mannan, but did not fully utilize them, solubilized and appeared to utilize pectic homogalacturonan, and did not solubilize RG-I.
Conclusions
The significant relative increase in RG-I in poplar solid residues following CBP indicates that C. thermocellum did not solubilize RG-I. These results support the hypothesis that this pectic glycan may be one barrier for efficient solubilization of poplar by C. thermocellum.
“…Even for the same feedstock variety, however, heterogeneity of the biomass quality is prevalent, and the result is an uncertain final product yield. Several recent studies have shown that multiple physicochemical properties comprehensively affect the biomass recalcitrance and the subsequent sugar release and/or fuel production [ 12 – 15 ]. Those factors include, but not limit to, cellulose crystallinity and degree of polymerization, lignin content, lignin S/G ratio, and lignin molecular weight.…”
BackgroundIn the biofuel industry, land productivity is important to feedstock growers and conversion process product yield is important to the biorefinery. The crop productivity, however, may not positively correlate with bioconversion yield. Therefore, it is important to evaluate sugar yield and biomass productivity. In this study, 2-year-old poplar trees harvested in the first coppice cycle, including one low-productivity hybrid and one high-productivity hybrid, were collected from two poplar tree farms. Through steam pretreatment and enzymatic hydrolysis, the bioconversion yields of low- and high-productivity poplar hybrids were compared for both sites.ResultsThe low-productivity hybrids had 9–19% higher sugar yields than the high-productivity hybrids, although they have the similar chemical composition. Economic calculations show the impact on the plantation and biorefinery of using the two feedstocks. Growing a high-productivity hybrid means the land owner would use 11–26% less land (which could be used for other crops) or collect $2.53–$3.46 MM/year extra revenue from the surplus feedstock. On the other side, the biorefinery would receive 5–10% additional revenue using the low-productivity hybrid.ConclusionWe propose a business model based on the integration of the plantation and the biorefinery. In this model, different feedstocks are assessed using a metric of product tonnage per unit land per year. Use of this new economic metric bridges the gap between feedstock growers and users to maximize the overall production efficiency.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1079-y) contains supplementary material, which is available to authorized users.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
