Stalk Hydrolysate Research Articles

Grape Stalk Valorization: An Efficient Re-Use of Lignocellulosic Biomass through Hydrolysis and Fermentation to Produce Lactic Acid from Lactobacillus rhamnosus IMC501

Lactobacillus rhamnosus is a homofermentative probiotic strain that was previously demonstrated to grow on lignocellulosic-derived raw materials and to convert glucose into L-lactic acid (LA) with yields that vary between 0.38 and 0.97 g/g. Lactic acid is a key platform chemical, largely applied in different biotechnological fields (spanning from the pharmaceutical to the food sector) and also as a building block for the production of biodegradable polymers. In the present study, grape stalks were evaluated as sources of fermentable sugars for the growth of L. rhamnosus IMC501 and for the production of LA, since millions of hectoliters of wine are produced every year worldwide, generating a huge amount of waste. Although grape stalks are quite recalcitrant, the combination of a steam explosion pre-treatment with optimized two-step hydrolysis and commercial enzymes (Cellic-CTec2) allowed us to obtain a cellulose conversion efficiency of about 37% and to develop small-scale 2 L batch fermentation processes. Results successfully demonstrate that L. rhamnosus IMC501 can tolerate biomass-derived inhibitors and grow on grape stalk hydrolysate without the need for additional sources of nitrogen or other nutritional elements, and that the strain can convert all glucose present in the medium into LA, reaching the maximal theoretical yield.

Engineering Corynebacterium glutamicum for de novo production of 2-phenylethanol from lignocellulosic biomass hydrolysate

Background2-Phenylethanol is a specific aromatic alcohol with a rose-like smell, which has been widely used in the cosmetic and food industries. At present, 2-phenylethanol is mainly produced by chemical synthesis. The preference of consumers for “natural” products and the demand for environmental-friendly processes have promoted biotechnological processes for 2-phenylethanol production. Yet, high 2-phenylethanol cytotoxicity remains an issue during the bioproduction process.ResultsCorynebacterium glutamicum with inherent tolerance to aromatic compounds was modified for the production of 2-phenylethanol from glucose and xylose. The sensitivity of C. glutamicum to 2-phenylethanol toxicity revealed that this host was more tolerant than Escherichia coli. Introduction of a heterologous Ehrlich pathway into the evolved phenylalanine-producing C. glutamicum CALE1 achieved 2-phenylethanol production, while combined expression of the aro10. Encoding 2-ketoisovalerate decarboxylase originating from Saccharomyces cerevisiae and the yahK encoding alcohol dehydrogenase originating from E. coli was shown to be the most efficient. Furthermore, overexpression of key genes (aroGfbr, pheAfbr, aroA, ppsA and tkt) involved in the phenylpyruvate pathway increased 2-phenylethanol titer to 3.23 g/L with a yield of 0.05 g/g glucose. After introducing a xylose assimilation pathway from Xanthomonas campestris and a xylose transporter from E. coli, 3.55 g/L 2-phenylethanol was produced by the engineered strain CGPE15 with a yield of 0.06 g/g xylose, which was 10% higher than that with glucose. This engineered strain CGPE15 also accumulated 3.28 g/L 2-phenylethanol from stalk hydrolysate.ConclusionsIn this study, we established and validated an efficient C. glutamicum strain for the de novo production of 2-phenylethanol from corn stalk hydrolysate. This work supplied a promising route for commodity 2-phenylethanol bioproduction from nonfood lignocellulosic feedstock.Graphical

Effects of the chromium content on anaerobic fermentation of chrome shaving collagen and rice straw juice.

This thesis investigated the effects of different chromium contents on the gas production characteristics of anaerobic fermentation by mixing the collagen solution obtained from the hydrolysis of chromium tannin chips by alkali-enzyme combination with rice stalk hydrolysate and the changes of system pH, VFA concentration, SCOD concentration, ammonia nitrogen concentration, and chromium concentration during anaerobic fermentation. The experimental results show that the highest total gas production and cumulative methane production are 1531.0mL/gVS and 761.2mL/gVS, respectively, with a Cr content of 5mg/L, and the methane content reaches 49.7%. The best SCOD removal rate is 54.54% at a C/N ratio of 20:1. The increase in SCOD concentration is decreased with increasing chromium content, but there is no significant change in ammonia nitrogen concentration. The highest rate of SCOD degradation is achieved with a chromium content of 5mg/L. The results of this thesis provide data support and theoretical guidance for the resource recovery of chromium leather shavings.

Genome mining discovery of hydrogen production pathway of Klebsiella sp. WL1316 fermenting cotton stalk hydrolysate.

Genome sequencing was used to identify key genes for the generation of hydrogen gas through cotton stalk hydrolysate fermentation by Klebsiella sp. WL1316. Genome annotation indicated that the genome size was 5.2Mb with GC content 57.6%. Xylose was metabolized in the pentose phosphate pathway via the conversion of xylose to xylulose in Klebsiella sp. WL1316. This strain contained diverse formate-hydrogen lyases and hydrogenases with gene numbers higher than closely related species. A metabolic network involving glucose, xylose utilisation, and fermentative hydrogen production was reconstructed. Metabolic analysis of key node metabolites showed that glucose and xylose metabolism influenced biomass synthesis and biohydrogen production. Formic acid accumulated during fermentation at 24-48h but decreased sharply after 48h, illustrating the splitting of formic acid to hydrogen gas during early-to-mid fermentation. The Kreb's cycle was the main competitive metabolic branch of biohydrogen synthesis at 24h of fermentation. Lactic and acetic acid fermentation and late ethanol accumulation competed the carbon skeleton of biohydrogen synthesis after 72h of fermentation, indicating that these competitive pathways are regulated in middle-to-late fermentation (48-96h). This study is the first to elucidate the metabolic mechanisms of mixed sugar utilisation and biohydrogen synthesis based on genomic information.

Coagulation Treatment of Corn Stalk Hydrolysates for Lignin-Derived Phenolic Compounds Removal, Improved Biomethane Production and Antioxidant Preparation

Coagulation Treatment of Corn Stalk Hydrolysates for Lignin-Derived Phenolic Compounds Removal, Improved Biomethane Production and Antioxidant Preparation

Improvement of Nicotine Removal and Ethanol Fermentability From Tobacco Stalk by Integration of Dilute Sulfuric Acid Presoak and Instant Catapult Steam Explosion Pretreatment.

The nicotine from tobacco stalk showed obvious inhibitory effect on the activity of cellulase and fermentability of microorganisms, which seriously hinders the utilization of tobacco stalk. Dilute sulfuric acid presoak of tobacco stalk was used to enhance the performance of instant catapult steam explosion (ICSE) for tobacco stalk pretreatment. The presoak was beneficial to break the recalcitrant structure of tobacco stalk, reduce nicotine content to relieve the inhibition on the activity of cellulase and metabolism of microorganisms, and promote the performance of enzymatic hydrolysis and ethanol fermentation. The optimized 0.8% sulfuric acid (w/w) presoak–integrated ICSE pretreatment resulted in 85.54% nicotine removal from tobacco stalk; meanwhile, the total sugar concentration from enzymatic hydrolysis of pretreated tobacco stalk increased from 33.40 to 53.81 g/L (the ratio of dry tobacco stalk to water was 1:8, w/w), ethanol concentration increased 103.36% from 5.95 to 12.10 g/L in flask, compared with separate ICSE pretreatment. Finally, the ethanol concentration achieved the highest 23.53 g/L in a 5-L fermenter with the ethanol yield from the glucose of tobacco stalk hydrolysate achieving 71.40% by increasing the solid loading of the tobacco stalk in the enzymatic hydrolysis process (the ratio of dry tobacco stalk to water was 1:4, w/w). These results achieved the expected purpose of efficient utilization of discarded tobacco stalk.

Metabolic pathway analysis of walnut endophytic bacterium Bacillus subtilis HB1310 related to lipid production from fermentation of cotton stalk hydrolysate based on genome sequencing

In this study, genome sequencing and metabolic analysis were used to identify and verify the key metabolic pathways for glucose and xylose utilization and fatty acid synthesis in the walnut endophytic bacterium (WEB) Bacillus subtilis HB1310. The genome sequence of WEB HB1310 was generated with a size of 4.1Mb and GC content of 43.5%. Genome annotation indicated that the Embden-Meyerhof-Parnas, pentose phosphate, and fatty acid synthesis pathways were mainly involved in mixed sugar utilization and lipid production. In particular, diverse and abundant fatty acid synthesis genes were observed in a higher number than in other Bacillus strains. The tricarboxylic acid cycle competitively shared the carbon flux flowing before 48h, and the acetic acid fermentation competed after 72h. Moreover, fatty acid synthase activity was highly correlated with lipid titer with a correlation coefficient of 0.9626, and NADPH might be more utilized for the lipid synthesis within 48h. This study is the first attempt to explain the metabolic mechanism of mixed sugar utilization and lipid production based on genomic information, which provides a theoretical basis for the metabolic regulation of bacterial lipid production from lignocellulosic hydrolysates.

Tyrosinase inhibitory performance of hydrolysate from post-washing liquor of steam exploded corn stalk and its fractionation enhancement

In this work, corn stalk was subjected to steam explosion (SE) pretreatment, and the hydrolysate in post-washing liquor of steam exploded corn stalk was assayed for anti-tyrosinase activity for the first time. The hydrolysate showed strong anti-tyrosinase activity with an IC50 of 2.17 mg/mL (inhibitor concentration when 50% of tyrosinase activity is inhibited) at SE severity of 4.20 (198 °C, 20 min). Through hydrolysate component profiles and model substance analysis, phenolic compounds (especially lignin-derived H-unit monomers and phenolic acids) were confirmed to be the major tyrosinase inhibitors in hydrolysate. To further improve the inhibitory activity, an enrichment process of phenolic compounds by ethyl-acetate fractionation of hydrolysate was employed. Ethyl-acetate soluble fraction exhibited significantly enhanced anti-tyrosinase activity (IC50, 0.29 mg/mL), which was even better than p-coumaric acid (a typical tyrosinase inhibitor with IC50 of 0.31 mg/mL). Additionally, the mixed-type inhibition of hydrolysate on tyrosinase was illustrated by kinetics study and the interaction between hydrolysate and tyrosinase was confirmed by fluorescence quenching measurement. Consequently, this work aims to evaluate and improve the anti-tyrosinase activity of hydrolysate from steam explosion processing of corn stalk, which opens new perspectives in potential application of currently underused corn stalk hydrolysate as a value-added tyrosinase inhibitor.

Enhanced biohydrogen production from cotton stalk hydrolysate of Enterobacter cloacae WL1318 by overexpression of the formate hydrogen lyase activator gene

BackgroundBiohydrogen production from lignocellulose has become an important hydrogen production method due to its diversity, renewability, and cheapness. Overexpression of the formate hydrogen lyase activator (fhlA) gene is a promising tactic for enhancement of hydrogen production in facultative anaerobic Enterobacter. As a species of Enterobacter, Enterobacter cloacae was reported as a highly efficient hydrogen-producing bacterium. However, little work has been reported in terms of cloning and expressing the fhlA gene in E. cloacae for lignocellulose-based hydrogen production.ResultsIn this study, the formate hydrogen lyase activator (fhlA) gene was cloned and overexpressed in Enterobacter cloacae WL1318. We found that the recombinant strain significantly enhanced cumulative hydrogen production by 188% following fermentation of cotton stalk hydrolysate for 24 h, and maintained improved production above 30% throughout the fermentation process compared to the wild strain. Accordingly, overexpression of the fhlA gene resulted in an enhanced hydrogen production potential (P) and maximum hydrogen production rate (Rm), as well as a shortened lag phase time (λ) for the recombinant strain. Additionally, the recombinant strain also displayed improved glucose (12%) and xylose (3.4%) consumption and hydrogen yield Y(H2/S) (37.0%) compared to the wild strain. Moreover, the metabolites and specific enzyme profiles demonstrated that reduced flux in the competitive branch, including succinic, acetic, and lactic acids, and ethanol generation, coupled with increased flux in the pyruvate node and formate splitting branch, benefited hydrogen synthesis.ConclusionsThe results conclusively prove that overexpression of fhlA gene in E. cloacae WL1318 can effectively enhance the hydrogen production from cotton stalk hydrolysate, and reduce the metabolic flux in the competitive branch. It is the first attempt to engineer the fhlA gene in the hydrogen-producing bacterium E. cloacae. This work provides a highly efficient engineered bacterium for biohydrogen production from fermentation of lignocellulosic hydrolysate in the future.

Enhanced Biohydrogen Production Influenced by Magnetic Nanoparticles Supplementation Using Enterobacter cloacae

The effects of synthesized magnetic nanoparticles (0–50 mg/L) on biohydrogen production from cotton stalk hydrolysate using Enterobacter cloacae were investigated, to find out the enhancement of the bacterial hydrogen production efficiency. The magnetic Fe3O4NPs with uniform size approximately 50 nm were well synthesized and applied in the fermentative hydrogen production system, accordingly, the addition of optimum concentration of 40 mg/L Fe3O4NPs resulted in the maximum daily hydrogen production, cumulative hydrogen production, glucose utilization, xylose utilization and hydrogen yield of 462.0 ± 9.6 mL, 1625.2 ± 18.0 mL/L, 84.29 ± 0.34%, 92.36 ± 0.16%, 0.37 ± 0.004 mol H2/mol sugar separately. Moreover, the dynamically fitted parameters of hydrogen production potential (P) and hydrogen production rate (Rm) increased to 1851.92 mL/L and 20.27 mL/(L h) respectively, and the lag phase time shortened to 1.30 h also following the addition of 40 mg/L Fe3O4NPs as compared with the control treatment (0 mg/L). These results indicated the positive effects of Fe3O4NPs supplementation on fermentative hydrogen production from cotton stalk hydrolysate by E. cloacae, revealing the feasibility of applying Fe3O4NPs supplementation for enhancement of such hydrogen production system.

Exploiting the NADPH pool for xylitol production using recombinant Saccharomyces cerevisiae.

Xylitol is a five-carbon sugar alcohol that has a variety of uses in the food and pharmaceutical industries. In xylose assimilating yeasts, NAD(P)H-dependent xylose reductase (XR) catalyzes the reduction of xylose to xylitol. In the present study, XR with varying cofactor specificities was overexpressed in Saccharomyces cerevisiae to screen for efficient xylitol production. Xylose consumption and xylitol yields were higher when NADPH-dependent enzymes (Candida tropicalis XR and S. cerevisiae Gre3p aldose reductase) were expressed, indicating that heterologous enzymes can utilize the intracellular NADPH pool more efficiently than the NADH pool, where they may face competition from native enzymes. This was confirmed by overexpression of a NADH-preferring C. tropicalis XR mutant, which led to decreased xylose consumption and lower xylitol yield. To increase intracellular NADPH availability for xylitol production, the promoter of the ZWF1 gene, coding for the first enzyme of the NADPH-generating pentose phosphate pathway, was replaced with the constitutive GPD promoter in a strain expressing C. tropicalis XR. This change led to a ~12% increase in xylitol yield. Deletion of XYL2 and SOR1, whose gene products can use xylitol as substrate, did not further increase xylitol yield. Using wheat stalk hydrolysate as source of xylose, the constructed strain efficiently produced xylitol, demonstrating practical relevance of this approach.

Effects of Fe0 and Ni0 nanoparticles on hydrogen production from cotton stalk hydrolysate using Klebsiella sp. WL1316: Evaluation of size and concentration of the nanoparticles

Fe0 and Ni0 nanoparticles (NPs) of certain size were synthesized and added to the hydrogen production system from cotton stalk hydrolysate using Klebsiella sp. WL1316. Fe0 and Ni0 NPs with a size of 50 nm at all concentrations effectively improve hydrogen production during mid to late fermentation stages; particularly, the highest daily hydrogen production obtained following treatment with 50 nm Fe0 NPs at 30 mg/L fermented for 96 h significantly increased by 61% comparing to the control treatment. The reducing sugar consumption in cotton stalk hydrolysate and ΔOD600 could be improved to some extent by Fe0 and Ni0 NPs supplementation. Addition of Fe0 or Ni0 NPs of 50 nm at a concentration of 30 mg/L resulted in enhanced cumulative hydrogen production with improvement of hydrogen yield reached higher than 20%, and the values of Y(H2/S) were all higher than 90 mL/g substrate, reflecting good hydrogen production and substrate consumption. The analysis of the main soluble metabolites profile revealed that supplementation with Fe0 and Ni0 NPs of suitable size and concentration may decrease the metabolic flux in the competitive branch of hydrogen production and increase the metabolic flux of the key node that leads to hydrogen generation, thus promoting biohydrogen synthesis.

Fermentative Biohydrogen Production with Enteric Bacteria Isolated from the Intestine of Wild Common Carp Dwelling in Tarim River Basin

The biological hydrogen generating from fermentation of low-cost lignocellulosic feedstocks by hydrogen-producing bacteria has attracted many attentions in recent years. In the present investigation, ten hydrogen-producing bacteria were newly isolated from the intestine of wild common carp (Cyprinus carpio L.), and identified belonging to the genera of Enterobacter and Klebsiella based on analysis of the 16S rDNA gene sequence and examination of the physiological and biochemical characteristics. All the isolates inherently owned the ability to metabolize xylose especially the cotton stalk hydrolysate for hydrogen production with hydrogen yield (HY) higher than 100 mL·L-1. In particular, two isolates, WL1306 and WL1305 obtained higher HY, hydrogen production rate (HPR), and hydrogen production potential (HPP) using cotton stalk hydrolysate as sugar substrate than the mixed sugar of glucose & xylose, which obtained the HY of 249.5 ± 29.0, 397.0 ± 36.7 mL·L-1, HPR of 10.4 ± 1.2, 16.5 ± 1.5 mL·L-1·h-1, HPP of 19.5 ± 2.3, 31.0 ± 2.8 mL·L-1·g-1sugar, separately. The generation of soluble metabolites, such as the lactate, formate, acetate, succinate and ethanol reflected the mixed acid fermentation properties of the hydrogen production pathway.

Engineering Microbial Consortia for High-Performance Cellulosic Hydrolyzates-Fed Microbial Fuel Cells.

Microbial fuel cells (MFCs) are eco-friendly bio-electrochemical reactors that use exoelectrogens as biocatalyst for electricity harvest from organic biomass, which could also be used as biosensors for long-term environmental monitoring. Glucose and xylose, as the primary ingredients from cellulose hydrolyzates, is an appealing substrate for MFC. Nevertheless, neither xylose nor glucose can be utilized as carbon source by well-studied exoelectrogens such as Shewanella oneidensis. In this study, to harvest the electricity by rapidly harnessing xylose and glucose from corn stalk hydrolysate, we herein firstly designed glucose and xylose co-fed engineered Klebsiella pneumoniae-S. oneidensis microbial consortium, in which K. pneumoniae as the fermenter converted glucose and xylose into lactate to feed the exoelectrogens (S. oneidensis). To produce more lactate in K. pneumoniae, we eliminated the ethanol and acetate pathway via deleting pta (phosphotransacetylase gene) and adhE (alcohol dehydrogenase gene) and further constructed a synthesis and delivery system through expressing ldhD (lactate dehydrogenase gene) and lldP (lactate transporter gene). To facilitate extracellular electron transfer (EET) of S. oneidensis, a biosynthetic flavins pathway from Bacillus subtilis was expressed in a highly hydrophobic S. oneidensis CP-S1, which not only improved direct-contacted EET via enhancing S. oneidensis adhesion to the carbon electrode but also accelerated the flavins-mediated EET via increasing flavins synthesis. Furthermore, we optimized the ratio of glucose and xylose concentration to provide a stable carbon source supply in MFCs for higher power density. The glucose and xylose co-fed MFC inoculated with the recombinant consortium generated a maximum power density of 104.7 ± 10.0 mW/m2, which was 7.2-folds higher than that of the wild-type consortium (12.7 ± 8.0 mW/m2). Lastly, we used this synthetic microbial consortium in the corn straw hydrolyzates-fed MFC, obtaining a power density 23.5 ± 6.0 mW/m2.

Two stage hydrogen production using maize stalk hydrolysate

Two stage hydrogen production using maize stalk hydrolysate

Production and characterization of bioethanol from Solanum lycopersicum stalk hydrolysates by the simultaneous saccharification and fermentation using Zymomonas mobilis and Saccharomyces cerevisae

Production and characterization of bioethanol from Solanum lycopersicum stalk hydrolysates by the simultaneous saccharification and fermentation using Zymomonas mobilis and Saccharomyces cerevisae

Production and characterization of bioethanol from Solanum lycopersicum stalk hydrolysates by the simultaneous saccharification and fermentation using Zymomonas mobilis and Saccharomyces cerevisae

The limited oil reserves, pollution concerns, global warming has led to an increased financial support for sustainable and environmental friendly sources of energy. In the last decades there is an increasing interest in the development of the bioethanol production from lignocellulosic residues, which do not compete directly with food. However, the low efficient conversion of cellulosic biomass to biofuels hinders its success hence the need to constantly explore new, cheap and readily available raw materials. In this work, the capability of typed strains of Z. mobilis, S. cerevisiae as well as the co culture of Z. mobilis and S. cerevisiae (1:1) to produce ethanol by saccharification and fermentation process from tomato stalk was investigated and compared. The results shows the optimal ethanol yield of 4.00, 6.70 and 10.97% (v/v) was obtained from S. cerevisiae, Z. mobilis and the co culture of S. cerevisiae and Z. mobilis after 6 days of fermentation. The combination of S. cerevisiae and Z. mobilis yielded the highest ethanol when compared with the yields obtained when the organisms were used separately since the combination of the bacteria and yeast undergoes EMP and ED pathways which converts sugar into alcohol. The identity of the produced ethanol was confirmed by its density and IR spectrum. The results of this study suggest that agro waste should no longer be discarded but converted to useful products like bioethanol since it contains fermentable sugars.

Succinate Production with Metabolically Engineered Escherichia coli Using Elephant Grass Stalk (Pennisetum purpureum) Hydrolysate as Carbon Source

Succinic acid is a spectacular chemical that can be used as the precursor of various industrial products including pharmaceuticals and biochemicals. The improvement of the succinic acid market depends on strains engineering that is capable of producing succinic acid at high yield and excellent growth rate which could utilize the wide range of carbon sources such as renewable biomass. Here we use counter selection using catAsacB for pathway design and strains developments. In this investigation, metabolically engineered Escherichia coli M6PM strain was constructed for the synthesis of succinic acid using elephant grass stalk (Pennisetum purpureum) as a carbon source. Elephant grass stalk hydrolysate was prepared which comprised of 11.60 ± 0.04 g/L glucose, 27.22 ± 0.04 g/L xylose and 0.65 ± 0.04 g/L arabinose. Metabolically engineered E. coli M6PM was constructed and fermentation with pure sugars revealed that it could utilize xylose and glucose efficiently. E. coli M6PM produced a final succinate concentration of 30.03 ± 0.02 g/L and a yield of 1.09 mol/mol during 72 h dual-phase fermentation using elephant grass stalk hydrolysate, which resulted in 64% maximum theoretical yield of succinic acid. The high succinate yield from elephant grass stalk demonstrated possible application of renewable biomass as feedstock for the synthesis of succinic acid using recombinant E. coli.

Metabolic engineering of Corynebacterium glutamicum for efficient production of succinate from lignocellulosic hydrolysate

BackgroundSuccinate has been recognized as one of the most important bio-based building block chemicals due to its numerous potential applications. However, efficient methods for the production of succinate from lignocellulosic feedstock were rarely reported. Nevertheless, Corynebacterium glutamicum was engineered to efficiently produce succinate from glucose in our previous study.ResultsIn this work, C. glutamicum was engineered for efficient succinate production from lignocellulosic hydrolysate. First, xylose utilization of C. glutamicum was optimized by heterologous expression of xylA and xylB genes from different sources. Next, xylA and xylB from Xanthomonas campestris were selected among four candidates to accelerate xylose consumption and cell growth. Subsequently, the optimal xylA and xylB were co-expressed in C. glutamicum strain SAZ3 (ΔldhAΔptaΔpqoΔcatPsod-ppcPsod-pyc) along with genes encoding pyruvate carboxylase, citrate synthase, and a succinate exporter to achieve succinate production from xylose in a two-stage fermentation process. Xylose utilization and succinate production were further improved by overexpressing the endogenous tkt and tal genes and introducing araE from Bacillus subtilis. The final strain C. glutamicum CGS5 showed an excellent ability to produce succinate in two-stage fermentations by co-utilizing a glucose–xylose mixture under anaerobic conditions. A succinate titer of 98.6 g L−1 was produced from corn stalk hydrolysate with a yield of 0.87 g/g total substrates and a productivity of 4.29 g L−1 h−1 during the anaerobic stage.ConclusionThis work introduces an efficient process for the bioconversion of biomass into succinate using a thoroughly engineered strain of C. glutamicum. To the best of our knowledge, this is the highest titer of succinate produced from non-food lignocellulosic feedstock, which highlights that the biosafety level 1 microorganism C. glutamicum is a promising platform for the envisioned lignocellulosic biorefinery.

Biohydrogen production from fermentation of cotton stalk hydrolysate by Klebsiella sp. WL1316 newly isolated from wild carp (Cyprinus carpio L.) of the Tarim River basin.

A new hydrogen-producing bacterium was isolated from the intestine of wild carp (Cyprinus carpio L.) of the Tarim River Basin. The isolate was identified as Klebsiella sp. based on 16S rDNA gene sequencing and examination of physiological and biochemical characteristics. The isolated strain, Klebsiella sp. WL1316, could effectively produce a high yield of hydrogen by using cotton stalk hydrolysate as substrate. The optimum fermentation conditions for hydrogen production were determined as follows: an initial sugar concentration of 40g/L, a fermentation temperature of 37°C and an initial pH value of 8.0. The scaled-up fermentation process was conducted in a 5-L fermenter using these parameters. Higher productivities with maximum daily hydrogen production of 937.0 ± 41.0mLL-1day-1, cumulative hydrogen production of 2908.5 ± 47.4mLL-1, viable cell count of (20.2 ± 0.6) × 108CFUmL-1 and hydrogen yield of 1.44 ± 0.08molmol-1sugarconsumed were obtained. The cumulative hydrogen production was predicted by the modified Gompertz equation with R 2 of 0.997, and values of R m and P were 44.8mLL-1h-1 and 3057.6mLL-1, respectively. These results indicated that the strain Klebsiella sp. WL1316 resulted in a high hydrogen production rate (HPR) and good hydrogen production potential. Moreover, this strain exhibited higher values of maximum hydrogen yield and HPR than the reported pure cultures.