Direct degradation of cellulosic biomass to bio-hydrogen from a newly isolated strain Clostridium sartagoforme FZ11

Utilization of plant-derived wastes as the potential biohydrogen source: a sustainable strategy for waste management

The sustainable economy has shown a renewed interest in acquiring access to the resources required to promote innovative practices that favor recycling and the reuse of existing, unconsidered things over newly produced ones. The production of biohydrogen through dark anaerobic fermentation of organic wastes is one of the intriguing possibilities for replacing fossil-based fuels through the circular economy. At present, plant-derived waste from the agro-based industry is the main global concern. When these wastes are improperly disposed of in landfills, they become the habitat for several pathogens. Additionally, it contaminates surface water as a result of runoff, and the leachate that is created from the waste enters groundwater and degrades its quality. However, cellulose and hemicellulose-rich plant wastes from agriculture fields and agro-based industries have been employed as the most efficient feedstock since carbohydrates are the primary substrate for the synthesis of biohydrogen. To produce biohydrogen from plant-derived wastes on a large scale, it is necessary to explore comprehensive knowledge of lab-scale parameters and pretreatment strategies. This paper summarizes the problems associated with the improper management of plant-derived wastes and discusses the recent developments in dark fermentation and substrate pretreatment techniques with the goal of gaining significant insight into the biohydrogen production process. It also highlights the utilization of anaerobic digestate, which is left over after biohydrogen gas as feedstock for the development of value-added products such as volatile fatty acids (VFA), biochar, and biofertilizer.

PandaGUT provides new insights into bacterial diversity, function, and resistome landscapes with implications for conservation

BACKGROUND

The gut microbiota play important roles in host adaptation and evolution, but are understudied in natural population of wild mammals. To address host adaptive evolution and improve conservation efforts of threatened mammals from a metagenomic perspective, we established a high-quality gut microbiome catalog of the giant panda (pandaGUT) to resolve the microbiome diversity, functional, and resistome landscapes using approximately 7 Tbp of long- and short-read sequencing data from 439 stool samples.

RESULTS

The pandaGUT catalog comprises 820 metagenome-assembled genomes, including 40 complete closed genomes, and 64.5% of which belong to species that have not been previously reported, greatly expanding the coverage of most prokaryotic lineages. The catalog contains 2.37 million unique genes, with 74.8% possessing complete open read frames, facilitating future mining of microbial functional potential. We identified three microbial enterotypes across wild and captive panda populations characterized by Clostridium, Pseudomonas, and Escherichia, respectively. We found that wild pandas exhibited host genetic-specific microbial structures and functions, suggesting host-gut microbiota phylosymbiosis, while the captive cohorts encoded more multi-drug resistance genes.

CONCLUSIONS

Our study provides largely untapped resources for biochemical and biotechnological applications as well as potential intervention avenues via the rational manipulation of microbial diversity and reducing antibiotic usage for future conservation management of wildlife. Video Abstract.

Clostridium btbubcensis BJN0001, a potentially new species isolated from the cellar mud of Chinese strong-flavor baijiu, produces ethanol, acetic acid and butyric acid from glucose

A novel strain, designated BJN0001, was isolated from the cellar mud of Chinese strong-flavor baijiu. The complete genome of strain BJN0001 was 2,688,791 bp and annotated with 2610 genes. Whole-genome similarity metrics such as average nucleotide identity (ANI) of BJN0001 with reference genomes reveals clear species boundaries of < 95% ANI value for species. The DNA-DNA hybridization (DDH) values of BJN0001 with the type species were all lower than 70% DDH value for species. Based on these results, the strain BJN0001 was considered a potentially new species of the genus Clostridium. Meanwhile, the fermentation characteristics indicated that the strain had the capability to convert glucose to ethanol, acetic acid and butyric acid, which could provide basic data for revealing its function in baijiu fermentation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03271-7.

Lignocellulose degradation in Protaetia brevitarsis larvae digestive tract: refining on a tightly designed microbial fermentation production line

BACKGROUND

The Scarabaeidae insect Protaetia brevitarsis (PB) has recently gained increasing research interest as a resource insect because its larvae can effectively convert decaying organic matter to plant growth-promoting frass with a high humic acid content and produce healthy, nutritional insect protein sources. Lignocellulose is the main component of PB larvae (PBL) feed, but PB genome annotation shows that PBL carbohydrate-active enzymes are not able to complete the lignocellulose degradation process. Thus, the mechanism by which PBL efficiently degrade lignocellulose is worthy of further study.

RESULTS

Herein, we used combined host genomic and gut metagenomic datasets to investigate the lignocellulose degradation activity of PBL, and a comprehensive reference catalog of gut microbial genes and host gut transcriptomic genes was first established. We characterized a gene repertoire comprising highly abundant and diversified lignocellulose-degrading enzymes and demonstrated that there was unique teamwork between PBL and their gut bacterial microbiota for efficient lignocellulose degradation. PBL selectively enriched lignocellulose-degrading microbial species, mainly from Firmicutes and Bacteroidetes, which are capable of producing a broad array of cellulases and hemicellulases, thus playing a major role in lignocellulosic biomass degradation. In addition, most of the lignocellulose degradation-related module sequences in the PBL microbiome were novel. PBL provide organic functional complementarity for lignocellulose degradation via their evolved strong mouthparts, alkaline midgut, and mild stable hindgut microenvironment to facilitate lignocellulosic biomass grinding, dissolving, and symbiotic microbial fermentation, respectively.

CONCLUSIONS

This work shows that PBL are a promising model to study lignocellulose degradation, which can provide highly abundant novel enzymes and relevant lignocellulose-degrading bacterial strains for biotechnological biomass conversion industries. The unique teamwork between PBL and their gut symbiotic bacterial microbiota for efficient lignocellulose degradation will expand the knowledge of holobionts and open a new beginning in the theory of holobionts. Video Abstract.

Isolation, identification, and biological characteristics of Clostridium sartagoforme from rabbit

In order to develop microbial additives for rabbit feed, a spore-forming bacteria was isolated from the feces of Hyla rabbit using reinforced clostridium medium (RCM). The 16S rDNA sequence of the bacterium was subjected to pairwise sequence alignment using BLAST; the colony morphology, and physiological, biochemical, and stress resistance were studied. The results showed that the bacterium was Clostridium sartagoforme, a gram positive anaerobe, which can produce spores. The colony diameter was 0.5 mm—2.5 mm, the diameter of the bacteria was 0.5 μm—1.0 μm × 2.0 μm—6.3 μm, and the spore diameter was 1 μm—1.2 μm × 1 μm—1.2 μm. C. sartagoforme can utilize various sugars and alcohols such as fructose, galactose, sorbitol, and inositol. It secreted cellulase into the extracellular environment to form a transparent hydrolysis circle in Congo red medium, it could not liquify gelatin, and the lysine decarboxylase reaction was positive. In liquid medium it entered the stable growth period after 9 h of inoculation. Additionally, it had good stress resistance with a survival rate that exceeded 53% after gastric juice (pH 2.5) treatment for 3 h, it grew in a medium with a bile salt concentration of 0.3%, and the survival rate exceeded 85% after 10 minutes at 80°C. Moreover, animal testing indicated that this strain has no adverse effects on the morbidity and mortality of rabbits. In summary, C. sartagoforme XN-T4 was isolated from rabbit feces. This bacterium has good resistance to stress, can decompose a variety of monosaccharides and polysaccharides including cellulose, which is relatively harmless for animal health.

Biochar reinforced the populations of cbbL-containing autotrophic microbes and humic substance formation via sequestrating CO2 in composting process

The quality of compost is drastically reduced due to the loss of carbon, which negatively impacts the environment. Carbon emission reduction and carbon dioxide (CO₂) fixation have attracted much attention in composting research. In this study, the relationship between CO₂ emission, humic substances (HS) formation and cbbL-containing autotrophic microbes (CCAM) was analyzed by adding biochar during cow manure composting. The results showed that biochar can facilitate the degradation of organic matter (OM) and formation of HS, as well as reinforce the diversity and abundance of CCAM community, thereby promoting CO₂ fixation and reducing carbon loss during composting. High-throughput sequencing analysis revealed significant increase in Actinobacteriota and Proteobacteria abundance by 30.97 % and 10.48 %, respectively, thus increasing carbon fixation by 32.07 %. Additionally, Alpha diversity index increased significantly during thermophilic phase, while Shannon index increased by 143.12 % and Sobs index increased by 51.62 %. Redundancy analysis (RDA) indicated that CO₂ was positively correlated with C/N, temperature, HS and dissolved organic matter (DOM), while the abundance of Paeniclostridium, Corynebacterium, Bifidobacterium, Clostridium, Turicibacter and Romboutsia were positively correlated with temperature, CO₂, C/N and E₂/E₄ (p <  0.01).

Direct Fermentative Hydrogen Production from Cellulose and Starch with Mesophilic Bacterial Consortia

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H2 consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H2/lmedium) and H2 yield (1.7 mol H2/molhexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H2/lmedium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles - 0.97 mol H2/molhexose (5.93 mmol H2/gcellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H2 production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H2/molhexose).

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H2 consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H2/lmedium) and H2 yield (1.7 mol H2/molhexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H2/lmedium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles – 0.97 mol H2/molhexose (5.93 mmol H2/gcellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H2 production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H2/molhexose).

Enhanced volatile fatty acid production from sago hampas by Clostridium beijerinckii SR1 for bioelectricity generation using microbial fuel cells

Sago hampas is a starch-based biomass from sago processing industries consisted of 58% remaining starch. This study has demonstrated the bioconversion of sago hampas to volatile fatty acids (VFAs) by Clostridium beijerinckii SR1 via anaerobic digestion. Higher total VFAs were obtained from sago hampas (5.04 g/L and 0.287 g/g) as compared to commercial starch (5.94 g/L and 0.318 g/g). The physical factors have been investigated for the enhancement of VFAs production using one-factor-at-a-time (OFAT). The optimum condition; 3% substrate concentration, 3 g/L of yeast extract concentration and 2 g/L of ammonium nitrate enhanced the production of VFAs by 52.6%, resulted the total VFAs produced is 7.69 g/L with the VFAs yield of 0.451 g/g. VFAs hydrolysate produced successfully generated 273.4 mV of open voltage circuit and 61.5 mW/m² of power density in microbial fuel cells. It was suggested that sago hampas provide as an alternative carbon feedstock for bioelectricity generation.

Identification of Hydrogen Gas Producing Anaerobic Bacteria Isolated from Sago Industrial Effluent

In this study, the biohydrogen production ability of isolated strains with sago industrial effluent in anaerobic batch fermentation was investigated. The bacteria responsible for the biohydrogen were isolated and identified as Clostridium sartagoforme NASGE 01 and Enterobacter cloacae NASGE 02. The volume of biohydrogen gas generated from the effluent was determined by gas chromatography (GC) and the organic acids formed during the biohydrogen production were determined by GC equipped with a flame ionization detector (GC-FID). In batch fermentation, C. sartagoforme NASGE 01 produced high amount of biogas (232 ± 11.02 mL/L) and biohydrogen (41.5%) followed by E. cloacae NASGE 02 produced 212.8 ± 8 mL/L biogas containing 31.5% of biohydrogen. Moreover, the hydrogen production potential (P), production rate (Rm) and lag time (λ) were analyzed from Gompertz non-linear curve fit model. The peak hydrogen yield was obtained with C. sartagoforme NASGE 01 was 158.7 mL/g glucose (1.26 mol H₂/mol glucose) with the substrate degradation of 56.7%. Butyric acid was the major organic acid formed while hydrogen production with Clostridium sartagoforme NASGE 01 (176.4 mg/L) and Enterobacter cloacae NASGE 02 (285.1 mg/L). These experimental data demonstrated the feasibility of biohydrogen production using pure culture of anaerobic bacteria with sago industrial waste water as substrate.

Isolation of Paraclostridium CR4 from sugarcane bagasse and its evaluation in the bioconversion of lignocellulosic feedstock into hydrogen by monitoring cellulase gene expression

Bioconversion of sugarcane bagasse (SCB) into hydrogen (H₂) and organic acids was evaluated using a biomolecular approach to monitor the quantity and expression of the cellulase (Cel) gene. Batch reactors at 37 °C were operated with Paraclostridium sp. (10% v/v) and different substrates (5 g/L): glucose, cellulose and SCB in natura and pre-heat treated and hydrothermally. H₂ production from glucose was 162.4 mL via acetic acid (2.9 g/L) and 78.4 mL from cellulose via butyric acid (2.9 g/L). H₂ production was higher in hydrothermally pretreated SCB reactors (92.0 mL), heat treated (62.5 mL), when compared to in natura SCB (51.4 mL). Butyric acid (5.8, 4.9 and 4.0 g/L) was the main acid observed in hydrothermally, thermally pretreated, and in natura SCB, respectively. In the reactors with cellulose and reactors with hydrothermally pretreated SCB, the Cel gene copy number 3 and 2 log were higher, respectively, during the stage of maximum H₂ production rate, when compared to the initial stage. Differences in Cel gene expression were observed according to the concentration of soluble sugars in the reaction medium. That is, there was no gene expression at the initial phase of the experiment using SCB with 2.6 g/L of sugars and increase of 2.2 log in gene expression during the phases with soluble sugars of <1.4 g/L.

Culture dependent and independent analyses suggest a low level of sharing of endospore-forming species between mothers and their children

Spore forming bacteria comprise a large part of the human gut microbiota. However, study of the endospores in gut microbiota is limited due to difficulties of culturing and numerous unknown germination factors. In this study we propose a new method for culture-independent characterization of endospores in stool samples. We have enriched DNA of spore-forming bacterial species from stool samples of 40 mother-child pairs from a previously described mother-child cohort. The samples were exposed to a two-step purification process comprising ethanol and ethidium monoazide (EMA) treatment to first kill vegetative cells and to subsequently eliminate their DNA from the samples. The composition of the ethanol-EMA resistant DNA was characterized by 16S rRNA marker gene sequencing. Operational taxonomic units (OTUs) belonging to the Clostridia class (OTU1: Romboutsia, OTU5: Peptostreptococcaceae and OTU14: Clostridium senso stricto) and one belonging to the Bacillus class (OTU20: Turicibacter) were significantly more abundant in the samples from mothers and children after ethanol-EMA treatment than in those treated with ethanol only. No correlation was observed between ethanol-EMA resistant OTUs detected in children and in their mothers, which indicates that a low level of spore-forming species are shared between mothers and their children. Anaerobic ethanol-resistant bacteria were isolated from all mothers and all children over 1 year of age. Generally, in 70% of the ethanol-treated samples used for anaerobic culturing, 16S rRNA gene sequences of bacterial isolates corresponded to OTUs detected in these samples after EMA treatment. We report a new DNA-based method for the characterization of endospores in gut microbiota. Our method has high degree of correspondence to the culture-based method, although it requires further optimization. Our results also indicate a high turnover of endospores in the gut during the first two years of life, perhaps with a high environmental impact.

Lignocellulosic hydrogen production using dark fermentation by Clostridium lentocellum strain Cel10 newly isolated from Ailuropoda melanoleuca excrement

Due to the characteristics of renewable and carbon-neutral, lignocellulose is considered to be one of the most potential, feasible, and ample resources for biofuel production on the Earth. However, the low energy conversion capacity of microorganisms is the primary bottleneck for utilizing lignocellulosic biomass to produce biofuel. In the present study, a mesophilic bacterial strain Cel10 identified as Clostridium lentocellum, according to 16S rRNA sequence homology, which can produce hydrogen from lignocellulose was isolated and characterized. The optimal conditions of hydrogen production from carboxymethylcellulose (CMC) are 37 °C, pH 7.0, and 5.0 g L-1. The H2 production peaked at 5.419 mmol H2 g-1 CMC under these conditions, which is relatively high compared to the other reported mesophilic bacteria that use cellulose as a substrate. Moreover, the H2-producing performance of strain Cel10 using cassava residues, a type of natural lignocellulosic feedstock, was also investigated. The results show that the hydrogen production peaked at 4.08 mmol H2 g-1 after 72 h of incubation, which is almost 1.2-3.8 times higher than the production of other mesophilic and thermophilic strains, while the highest cassava residues degradation rate reached 45.43%. The results validate that Clostridium lentocellum strain Cel10, newly isolated from Ailuropoda melanoleuca excrement, can offer a new method for directly converting lignocellulosic biomass to bio-hydrogen.

Optimization of hydrogen and organic acids productions with autochthonous and allochthonous bacteria from sugarcane bagasse in batch reactors

The individual and mutual effects of substrate concentration (from 0.8 to 9.2 g/L) and pH (from 4.6 to 7.4) on hydrogen and volatile fatty acids production from sugarcane bagasse (SCB) were investigated in batch reactors, using a response surface methodology (RSM) and central composite design (CCD). The maximum of 23.10 mmoL H₂/L was obtained under optimized conditions of 7.0 g SCB/L and pH 7.2, at 37 °C through the acetic acid pathway (1.57 g/L). Butyric and succinic acids were the major volatile fatty acids (VFA) produced in the fermentation process (from 0.66 to 1.88 g/L and from 1.06 to 1.65 g/L, respectively). According to the results, the RSM and CCD were useful tools to achieve high hydrogen production rates using Clostridium, Bacillus and Enterobacter, identified by Illumina sequencing (16S RNAr) in the fermentative consortium, and Clostridium and Paenibacillus, autochthonous bacteria from SCB. Significant changes were observed in the microbial community according to the changes in the independent variables, since the genera in the central point condition (5.0 g SCB/L and pH 6.0) were Lactobacillus, Escherichia and Clostridium, and Bacteroides and Enterobacter, which were identified in the optimized condition (7.0 g SCB/L and pH 7.2).

Diversity, Function, and Application of Clostridium in Chinese Strong Flavor Baijiu Ecosystem: A Review

Baijiu is a Chinese traditional distilled liquor with an annual yield over 13.12 million tons. Strong flavor baijiu (SFB) also called Luzhou-flavor liquor, takes account for > 70% of the total baijiu produced. SFB is produced by an open solid fermentation process with a complex microbial ecosystem. Clostridium is one of the most important microorganisms for the formation of the main flavor compounds of SFB, such as ethyl caproate. In this paper, we review current research progress on the Clostridium in the SFB ecosystem, focusing on the species diversity, physiological and metabolic features along with interspecies interactions. Systems biology approaches for the study of Clostridium from SFB ecosystems were discussed and explored. Furthermore, current applications of Clostridium in SFB production were discussed.

PRACTICAL APPLICATION

Strong flavor baijiu (SFB) accounts for more than 70% of total yield of Chinese baijiu, which exists for hundreds of years. Clostridium is common in SFB ecosystem and identified to be one of main contributors of flavor compounds in SFB. Study on the Clostridium from SFB ecosystem is not only helpful for the understanding of flavor compounds formation mechanism, but also the improvement of SFB quality. This study focuses on the current researches on the Clostridium species in SFB ecosystem, including the species diversity, physiological and metabolic features, and applications.

Characterization and mechanism analysis of lincomycin biodegradation with Clostridium sp. strain LCM-B isolated from lincomycin mycelial residue (LMR)

Lincomycin mycelial residue (LMR) is the restricted resource because it contains residual lincomycin, which is producing potential risks to the environment and human health. In this study, lincomycin-degrading strain LCM-B was isolated and identified as Clostridium sp. in the LMR. Strain LCM-B was able to degrade 62.03% of lincomycin at the initial concentration of 100 mg L^-1 after incubation for 10 d, while only 15.61% of lincomycin was removed at the initial concentration of 500 mg L^-1. The removal efficiency of lincomycin by strain LCM-B decreased as the initial concentration increased. Gene lnuB (which encodes the nucleotidyl transferase) was detected in the isolated strain, and it was proven to participate in lincomycin biodegradation based on the analysis of degradation products and pathway. The results provide a relatively complete understanding of lincomycin biodegradation mechanism. Strain LCM-B is promising to eliminate lincomycin from the LMR.

Biodegradation of 2-hydroxyl-1,4 naphthoquinone (lawsone) by Pseudomonas taiwanensis LH-3 isolated from activated sludge

2-hydroxy-1,4 naphthoquinone (lawsone) is widely used and induces environmental pollutions during its production and application. In the present study, a lawsone-degrading bacterium strain, LH-3 was successfully isolated from the activated sludge. Based on the 16S rRNA gene analysis, the strain LH-3 phylogenetically belonged to the Pseudomonas taiwanensis. It could degrade 200 mg L⁻¹ lawsone completely in 9 h with an inoculum quantity of 1% (v/v). The effects of environmental conditions on the degradation process and the degradation pathway were systematically investigated. LH-3 could maintain its high degradation efficiency under high salt condition. The identified intermediates of salicylic acid, 2-hydroxy-4-oxo-chroman-2-carboxylic acid, and catechol elucidated the potential degradation pathway. Furthermore, the immobilized LH-3 strain cells prepared with alginate gel and biochar performed excellent stability in nine successive degradation runs. It could sucessfully survive in laboratory scale sequencing batch reactor and become to be the dominant species. This study clearly revealed that LH-3 could serve as an attractive candidate for the microbial remediation of lawsone-containing wastewater.

Characterization of lignocellulosic compositions' degradation during chicken manure composting with added biochar by phospholipid fatty acid (PLFA) and correlation analysis

Biorefractory high polymer lignocellulosic compositions may limit rapid composting and stable decomposition. Because their degradation during composting is not well understood, the correlation with microbial community profiles was assessed to reveal degradation mechanism of lignocellulosic compositions. Testing of chicken manure aerobic composting with added biochar was performed using phospholipid fatty acid (PLFA) and correlation analysis. Results demonstrated a good composting effect with good dynamic correlation between microbial characteristic (PLFA) and lignocellulosic compositions' degradation ratio. The prediction model for hemicellulose degradation ratio (R²=0.97, SEP=3.24) and the prediction model for cellulose degradation ratio (R³=0.94, SEP=3.09), built using PLFA 16:0-18:2ω6c and PLFA 18:2ω6c-18:3ω3 as the arguments had good predictive ability. Based on microbial analysis and quantitative characterization of the degradation ratio, the prediction models provided methodological support for delineating the mechanism of lignocellulosic compositions' degradation during chicken manure aerobic composting with added biochar.

Direct hydrogen production from dilute-acid pretreated sugarcane bagasse hydrolysate using the newly isolated Thermoanaerobacterium thermosaccharolyticum MJ1

Background

Energy shortage and environmental pollution are two severe global problems, and biological hydrogen production from lignocellulose shows great potential as a promising alternative biofuel to replace the fossil fuels. Currently, most studies on hydrogen production from lignocellulose concentrate on cellulolytic microbe, pretreatment method, process optimization and development of new raw materials. Due to no effective approaches to relieve the inhibiting effect of inhibitors, the acid pretreated lignocellulose hydrolysate was directly discarded and caused environmental problems, suggesting that isolation of inhibitor-tolerant strains may facilitate the utilization of acid pretreated lignocellulose hydrolysate.

Results

Thermophilic bacteria for producing hydrogen from various kinds of sugars were screened, and the new strain named MJ1 was isolated from paper sludge, with 99% identity to Thermoanaerobacterium thermosaccharolyticum by 16S rRNA gene analysis. The hydrogen yields of 11.18, 4.25 and 2.15 mol-H₂/mol sugar can be reached at an initial concentration of 5 g/L cellobiose, glucose and xylose, respectively. The main metabolites were acetate and butyrate. More important, MJ1 had an excellent tolerance to inhibitors of dilute-acid (1%, g/v) pretreated sugarcane bagasse hydrolysate (DAPSBH) and could efficiently utilize DAPSBH for hydrogen production without detoxication, with a production higher than that of pure sugars. The hydrogen could be quickly produced with the maximum hydrogen production reached at 24 h. The hydrogen production reached 39.64, 105.42, 111.75 and 110.44 mM at 20, 40, 60 and 80% of DAPSBH, respectively. Supplementation of CaCO₃ enhanced the hydrogen production by 21.32% versus the control.

Conclusions

These results demonstrate that MJ1 could directly utilize DAPSBH for biohydrogen production without detoxication and can serve as an excellent candidate for industrialization of hydrogen production from DAPSBH. The results also suggest that isolating unique strains from a particular environment offers an ideal way to conquer the related problems.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0692-y) contains supplementary material, which is available to authorized users.

Characteristics of rumen microorganisms involved in anaerobic degradation of cellulose at various pH values

Microbial degradation of straw, the main by-product of agricultural production, has proved to be the most economical and effective means of producing hydrogen.

New combination of xylanolytic bacteria isolated from the lignocellulose degradation microbial consortium XDC-2 with enhanced xylanase activity

Three bacterial strains with extracellular xylanase activity were isolated from the microbial consortium XDC-2. The aerobic strain A7, belonging to Bacillus sp., was combined with the anaerobe Clostridium sp. strain AA3 and/or Bacteroides sp. strain AA4 to obtain an efficient natural xylanolytic complex enzyme. The synthetic microbial community M1 consisting of strains Bacillus and Clostridium showed enhanced extracellular xylanase activity and production, and higher lignocelluloses degradation capability than any of the pure cultures and other synthetic microbial communities. Neither corn straw degradation nor extracellular xylanase activity was enhanced in the other synthetic microbial communities, Bacillus, Bacteroides with or without Clostridium. Quantitative polymerase chain reaction showed that the aerobic strain Bacillus enabled the growth of the anaerobic strain Clostridium, but not that of the anaerobic strain Bacteroides. These findings suggest that strains Bacillus and Clostridium can coexist well and have a positive synergistic interaction for extracellular xylanase secretion and lignocellulose degradation.

A review on bioconversion of lignocellulosic biomass to H2: Key challenges and new insights

With the increasing energy crisis and rising concern over climate change, the development of clean alternative energy sources is of great importance. Biohydrogen produced from lignocellulosic biomass is a promising candidate, because of its positives such as readily available, no harmful emissions, environment friendly, efficient, and renewable. However, obstacles still exist to enable the commercialization of biological hydrogen production from lignocellulosic biomass. Thus the objective of this work is to provide update information about the recent progress on lignocellulosic hydrogen conversion via dark fermentation. In this review, the most important technologies associated with lignocellulosic hydrogen fermentation were covered. Firstly, pretreatment methods for better utilization of lignocellulosic biomass are presented, at the same time, hydrolysis methods assisting to achieve efficient hydrogen fermentation were discussed. Afterwards, issues related to bioprocesses for hydrogen production purposes were presented. Additionally, the paper gave challenges and new insights of lignocellulosic biohydrogen production.

Sustainable hydrogen production from bio-oil model compounds (meta-xylene) and mixtures (1-butanol, meta-xylene and furfural)

In the present work m-xylene and an equimolecular mixture of m-xylene, 1-butanol and furfural, all of them bio-oil model compounds, were studied in steam reforming (SR) conditions. Three different nickel catalysts, which showed to be active in 1-butanol SR (Ni/Al2O3, Ni/CeO2-Al2O3 and Ni/La2O3-Al2O3), were tested and compared with thermodynamic equilibrium values. Tests were carried out at temperatures from 800 to 600°C at atmospheric pressure with a steam to carbon ratio (S/C) of 5.0. Despite the different bio-oils fed, the amount of moles going through the catalytic bed was kept constant in order to obtain comparable results. After their use, catalysts were characterized by different techniques and those values were correlated with the activity results. All catalysts were deactivated during the SR of the mixture, mainly by coking. The highest hydrogen yields were obtained with Ni/Al2O3 and Ni/CeO2-Al2O3 catalysts in the SR of m-xylene and SR of the mixture, respectively.

Biohythane production from organic wastes: present state of art

The economy of an industrialized country is greatly dependent on fossil fuels. However, these nonrenewable sources of energy are nearing the brink of extinction. Moreover, the reliance on these fuels has led to increased levels of pollution which have caused serious adverse impacts on the environment. Hydrogen has emerged as a promising alternative since it does not produce CO2 during combustion and also has the highest calorific value. The biohythane process comprises of biohydrogen production followed by biomethanation. Biological H2 production has an edge over its chemical counterpart mainly because it is environmentally benign. Maximization of gaseous energy recovery could be achieved by integrating dark fermentative hydrogen production followed by biomethanation. Intensive research work has already been carried out on the advancement of biohydrogen production processes, such as the development of suitable microbial consortium (mesophiles or thermophiles), genetically modified microorganism, improvement of the reactor designs, use of different solid matrices for the immobilization of whole cells, and development of two-stage process for higher rate of H2 production. Scale-up studies of the dark fermentation process was successfully carried out in 20- and 800-L reactors. However, the total gaseous energy recovery for two stage process was found to be 53.6 %. From single-stage H2 production, gaseous energy recovery was only 28 %. Thus, two-stage systems not only help in improving gaseous energy recovery but also can make biohythane (mixture of H2 and CH4) concept commercially feasible.

Direct hydrogen production from lignocellulose by the newly isolated Thermoanaerobacterium thermosaccharolyticum strain DD32

The comparison of hydrogen production by conventional process and consolidated bioprocessing.