A novel thermoacidophilic endoglucanase, Ba-EGA, from a new cellulose-degrading bacterium, Bacillus sp.AC-1

Temporally-coordinated bivalent histone modifications of BCG1 enable fungal invasion and immune evasion

Bivalent histone modifications, including functionally opposite H3K4me3 and H3K27me3 marks simultaneously on the same nucleosome, control various cellular processes by fine-tuning the gene expression in eukaryotes. However, the role of bivalent histone modifications in fungal virulence remains elusive. By mapping the genome-wide landscape of H3K4me3 and H3K27me3 dynamic modifications in Fusarium graminearum (Fg) during invasion, we identify the infection-related bivalent chromatin-marked genes (BCGs). BCG1 gene, which encodes a secreted Fusarium-specific xylanase containing a G/Q-rich motif, displays the highest increase of bivalent modification during Fg infection. We report that the G/Q-rich motif of BCG1 is a stimulator of its xylanase activity and is essential for the full virulence of Fg. Intriguingly, this G/Q-rich motif is recognized by pattern-recognition receptors to trigger plant immunity. We discover that Fg employs H3K4me3 modification to induce BCG1 expression required for host cell wall degradation. After breaching the cell wall barrier, this active chromatin state is reset to bivalency by co-modifying with H3K27me3, which enables epigenetic silencing of BCG1 to escape from host immune surveillance. Collectively, our study highlights how fungal pathogens deploy bivalent epigenetic modification to achieve temporally-coordinated activation and suppression of a critical fungal gene, thereby facilitating successful infection and host immune evasion.

Effects of fermentation chamber temperature on microbes and quality of cigar wrapper tobacco leaves

The natural fermentation of cigar tobacco leaves usually utilizes natural temperature and humidity for fermentation. Cigars produced in China are often fermented in winter, and the low environmental temperatures can lead to slow heating of the tobacco stack, affecting the cigar tobacco leaves quality. This study aimed to determine the minimum chamber temperature required to initiate the process of fermentation for cigar tobacco leaves and to explore the impact of temperature on the microbial community of tobacco leaves. Here, the cigar variety "Dexue 1" were subjected to stacking fermentation under three temperature parameters (20 ℃, 27 ℃, 34 ℃). With an increase in environmental temperature, the temperature inside the stack of cigar leaves increased significantly, the protein, total sugar, starch, and total alkaloid content in fermented tobacco leaves decreased, and the aroma components and amino acid content increased. Microbial richness and community diversity associated with fermented tobacco were highest at chamber temperatures of above 27 ℃. The relative abundance of Chryseobacterium and Rhodococcus was significantly negatively correlated with protein, alkaloids, total sugar, and starch, and positively correlated with amino acids and aroma components. Chryseobacterium and Rhodococcus may be responsible for the degradation of macromolecular substances and the conversion of favorable aromatic substances, thus improving the tobacco leaves quality. This study demonstrated that increasing the fermentation chamber temperature above 27 ℃ was conductive to raising the inner-stack temperature, increased microbial diversity and aromatic quality, reduced the strength and irritation, and extremely enhanced the overall quality of fermented cigar tobacco leaves. KEY POINTS: • The environmental temperature of the fermentation chamber has a significant impact on the quality of tobacco • Temperature > 27 ℃ can initiate the process of cigar tobacco leaves fermentation and increase inner-stack temperature and microbial diversity and abundance • Chryseobacterium and Rhodococcus may be related to the degradation of macromolecular substances and the transformation of aromatic substances, thereby improving the quality of tobacco leaves.

Purification and enzymatic properties of a new thermostable endoglucanase from Aspergillus oryzae HML366

Aspergillus oryzae HML366 is a newly screened cellulase-producing strain. The endoglucanase HML ED1 from A. oryzae HML366 was quickly purified by a two-step method that combines ammonium sulfate precipitation and strong anion exchange column. SDS-PAGE electrophoresis indicated that the molecular weight of the enzyme was 68 kDa. The optimum temperature of the purified endoglucanase was 60 ℃ and the enzyme activity was stable below 70 ℃. The optimum pH was 6.5, and the enzyme activity was stable at pH between 4.5 and 9.0. The analysis indicated that additional Na⁺, K⁺, Ca²⁺, and Zn²⁺ reduced the catalytic ability of enzyme to the substrate, but Mn²⁺ enhanced its catalytic ability to the substrate.The Km and Vmax of the purified endoglucanase were 8.75 mg/mL and 60.24 μmol/min·mg, respectively. In this study, we report for the first time that A. oryzae HML366 can produce a heat-resistant and wide pH tolerant endoglucanase HML ED1, which has potential industrial application value in bioethanol, paper, food, textile, detergent, and pharmaceutical industries.

Highly efficient, processive and multifunctional recombinant endoglucanase RfGH5_4 from Ruminococcus flavefaciens FD-1 v3 for recycling lignocellulosic plant biomasses

Gene encoding endoglucanase, RfGH5_4 from R. flavefaciens FD-1 v3 was cloned, expressed in Escherichia coli BL21(DE3) cells and purified. RfGH5_4 showed molecular size 41 kDa and maximum activity at pH 5.5 and 55 °C. It was stable between pH 5.0-8.0, retaining 85% activity and between 5 °C-45 °C, retaining 75% activity, after 60 min. RfGH5_4 displayed maximum activity (U/mg) against barley β-D-glucan (665) followed by carboxymethyl cellulose (450), xyloglucan (343), konjac glucomannan (285), phosphoric acid swollen cellulose (86), beechwood xylan (21.7) and carob galactomannan (16), thereby displaying the multi-functionality. Catalytic efficiency (mL.mg^-1 s^-1) of RfGH5_4 against carboxymethyl cellulose (146) and konjac glucomannan (529) was significantly high. TLC and MALDI-TOF-MS analyses of RfGH5_4 treated hydrolysates of cellulosic and hemicellulosic polysaccharides displayed oligosaccharides of degree of polymerization (DP) between DP2-DP11. TLC, HPLC and Processivity-Index analyses revealed RfGH5_4 to be a processive endoglucanase as initially, for 30 min it hydrolysed cellulose to cellotetraose followed by persistent release of cellotriose and cellobiose. RfGH5_4 yielded sufficiently high Total Reducing Sugar (TRS, mg/g) from saccharification of alkali pre-treated sorghum (72), finger millet (62), sugarcane bagasse (38) and cotton (27) in a 48 h saccharification reaction. Thus, RfGH5_4 can be considered as a potential endoglucanase for renewable energy applications.

Composition and diversity of gut microbiota in Pomacea canaliculata in sexes and between developmental stages

Background

The apple snail, Pomacea canaliculata, is one of the world’s 100 worst invasive alien species and vector of some pathogens relevant to human health.

Methods

On account of the importance of gut microbiota to the host animals, we compared the communities of the intestinal microbiota from P. canaliculata collected at different developmental stages (juvenile and adult) and different sexes by using high-throughput sequencing.

Results

The core bacteria phyla of P. canaliculata gut microbiota included Tenericutes (at an average relative abundance of 45.7 %), Firmicutes (27.85 %), Proteobacteria (11.86 %), Actinobacteria (4.45 %), and Cyanobacteria (3.61 %). The female group possessed the highest richness values, whereas the male group possessed the lowest bacterial richness and diversity compared with the female and juvenile group. Both the developmental stages and sexes had important effects on the composition of the intestinal microbiota of P. canaliculata. By LEfSe analysis, microbes from the phyla Proteobacteria and Actinobacteria were enriched in the female group, phylum Bacteroidetes was enriched in the male group, family Mycoplasmataceae and genus Leuconostoc were enriched in the juvenile group. PICRUSt analysis predicted twenty-four metabolic functions in all samples, including general function prediction, amino acid transport and metabolism, transcription, replication, recombination and repair, carbohydrate transport and metabolism, etc.

Conclusions

This study provided a general understanding of the diversity characteristics of intestinal microbial communities of P. canaliculata, and indicated that developmental stage and gender could both influence the intestinal microbes of P. canaliculata. Further study may focus on the interaction between the gut microbiota and their host.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02259-2.

Microbial community and metabolic function analysis of cigar tobacco leaves during fermentation

Cigar tobacco leaves (CTLs) contain abundant bacteria and fungi that are vital to leaf quality during fermentation. In this study, artificial fermentation was used for the fermentation of CTLs since it was more controllable and efficient than natural aging. The bacterial and fungal community structure and composition in unfermented and fermented CTLs were determined to understand the effects of microbes on the characteristics of CTLs during artificial fermentation. The relationship between the chemical contents and alterations in the microbial composition was evaluated, and the functions of bacteria and fungi in fermented CTLs were predicted to determine the possible metabolic pathways. After artificial fermentation, the bacterial and fungal community structure significantly changed in CTLs. The total nitrate and nicotine contents were most readily affected by the bacterial and fungal communities, respectively. FAPROTAX software predictions of the bacterial community revealed increases in functions related to compound transformation after fermentation. FUNGuild predictions of the fungal community revealed an increase in the content of saprotrophic fungi after fermentation. These data provide information regarding the artificial fermentation mechanism of CTLs and will inform safety and quality improvements.

Thermotolerant glycosyl hydrolases-producing Bacillus aerius CMCPS1 and its saccharification efficiency on HCR-laccase (LccH)-pretreated corncob biomass

BACKGROUND

The current production of bioethanol based on lignocellulosic biomass (LCB) highly depends on thermostable enzymes and extremophiles owing to less risk of contamination. Thermophilic bacterial cellulases are preferred over fungi due to their higher growth rate, presence of complex multi-enzymes, stability, and enhanced bioconversion efficiency. Corncob, underutilized biomass, ensures energy conservation due to high lignocellulosic and more fermentable sugar content. In the present study, the thermophilic bacterium Bacillus aerius CMCPS1, isolated from the thermal springs of Manikaran, Himachal Pradesh, India, was characterized in terms of its activity, stability, and hydrolytic capacity. A two-step process comprising: (i) a combined strategy of hydrodynamic cavitation reaction (HCR)-coupled enzymatic (LccH at 6.5 U) pretreatment for delignification and (ii) subsequent hydrolysis of pre-treated (HCR-LccH) corncob biomass (CCB) using a thermostable cocktail of CMCPS1 was adopted to validate the efficiency of the process. Some of the parameters studied include lignin reduction, cellulose increase, and saccharification efficiency.

RESULT

Among the five isolates obtained by in situ enrichment on various substrates, B. aerius CMCPS1, isolated from hot springs, exhibited the maximum hydrolytic activity of 4.11. The GH activity of the CMCPS1 strain under submerged fermentation revealed maximum filter paper activity (FPA) and endoglucanase activity of 4.36 IU mL-1 and 2.98 IU mL-1, respectively, at 44 h. Similarly, the isolate produced exoglucanase and β-glucosidase with an activity of 1.76 IU mL-1 and 1.23 IU mL-1 at 48 h, respectively. More specifically, the enzyme endo-1,4-β-d glucanase E.C.3.2.1.4 (CMCase) produced by B. aerius CMCPS1 displayed wider stability to pH (3-9) and temperature (30-90 °C) than most fungal cellulases. Similarly, the activity of CMCase increased in the presence of organic solvents (118% at 30% acetone v/v). The partially purified CMCase from the culture supernatant of CMCPS1 registered 64% yield with twofold purification. The zymogram and SDS-PAGE analyses further confirmed the CMCase activity with an apparent molecular mass of 70 kDa. The presence of genes specific to cellulases, such as cellulose-binding domain CelB, confirmed the presence of GH family 46 and β-glucosidase activity (GH3). The multifunctional cellulases of CMCPS1 were evaluated for their saccharification efficiency on laccase (LccH, a fungal laccase from Hexagonia hirta MSF2)-pretreated corncob in a HCR. The lignin and hemicelluloses removal efficiency of HCR-LccH was 54.1 and 6.57%, respectively, with an increase in cellulose fraction (42.25%). The saccharification efficiency of 55% was achieved with CMCPS1 multifunctional cellulases at 50 °C and pH 5.0.

CONCLUSION

The multifunctional cellulase complex of B. aerius CMCPS1 is a potential biocatalyst for application in lignocellulosic biomass-based biorefineries. The saccharification ability of HCR-LccH-pretreated corncob at elevated temperatures would be an advantage for biofuel production from lignocellulosic biomass.

Production and characterization of an enzyme extract with cellulase activity produced by an indigenous strain of Fusarium verticillioides ITV03 using sweet sorghum bagasse

OBJECTIVES

To evaluate a strain of Fusarium verticillioides ITV03 isolated from wood residues in the Veracruz region of Mexico. Endoglucanase and β-glucosidase production by submerged fermentation was optimized using a Box-Behnken design, where the independent variables were urea, ammonium sulfate and yeast extract.

RESULTS

After optimization, an endoglucanase activity of 0.27 U/mL was achieved; subsequently, three carbon sources were evaluated (carboxymethyl cellulose, sweet sorghum bagasse cellulose and delignified sweet sorghum bagasse (DSSB). The results showed that DSSB yielded the greatest endoglucanase (0.28 U/mL) and β-glucosidase (0.12 U/mL) activities. Both enzymatic activities were characterized for the effect of pH, temperature and thermostability. The optimal parameters of β-glucosidase and endoglucanase activity were pH 5 and 4 respectively, the optimum temperature 60 °C. These enzymes were stable at 50 °C for 150.68 h and 8.54 h, with an activation energy (E_a(day)) of 265.55 kJ/mol and 44.40 kJ/mol respectively, for β-glucosidase and endoglucanase.

CONCLUSION

The present work shows that a native strain like F. verticillioides ITV03 using DSSB supplemented with nitrogen has a great potential as a producer of cellulase for lignocellulosic residue hydrolysis.

Purification and Biochemical Characterization of Alkalophilic Cellulase from the Symbiotic Bacillus subtilis BC1 of the Leopard Moth, Zeuzera pyrina (L.) (Lepidoptera: Cossidae)

In the current study, an extracellular cellulase belonging to symbiotic Bacillus subtilis Bc1 of the leopard moth is purified and characterized. The molecular mass of enzyme was 47.8 kDa using SDS-PAGE. The purified enzyme had optimum activity in temperature and pH around 60 °C and 8, respectively. The purified cellulase was introduced as a stable enzyme in a wide variety of temperature (20-80 °C) and pH (4-10) and remained active to more than 74% at 80 °C for 1 h. Moreover, the cellulase extremely was stabled in the presence of metal ions and organic solvents and its activity was increased by acetone (20% v/v), CaCl₂ and CoCl₂ and inhibited by MnCl₂ and NiCl₂. The values of enzyme's K_m and V_max were found to be 1.243 mg/mL and 271.3 µg/mL/min, respectively. The purified cellulase hydrolyzed cellulose, avicel and carboxymethyl cellulose (CMC) and the final product of CMC hydrolysis was cellobiose using thin-layer chromatography analysis. Consequently, owing to exo/endoglucanase activity and organic solvent, temperature and pH stability of the purified cellulase belong to B. subtilis BC1, it can be properly employed for various industrial purposes.

Integrative Proteomic Analysis of Digestive Tract Glycosidases from the Invasive Golden Apple Snail, Pomacea canaliculata

The freshwater snail Pomacea canaliculata, an invasive species of global significance, possesses a well-developed digestive system and diverse feeding mechanisms enabling the intake of a wide variety of food. The identification of glycosidases in adult snails would increase the understanding of their digestive physiology and potentially generate new opportunities to eradicate and/or control this invasive species. In this study, liquid chromatography coupled to tandem mass spectrometry was applied to define the occurrence, diversity, and origin of glycoside hydrolases along the digestive tract of P. canaliculata. A range of cellulases, hemicellulases, amylases, maltases, fucosidases, and galactosidases were identified across the digestive tract. The digestive gland and the contents of the crop and style sac yield a higher diversity of glycosidase-derived peptides. Subsequently, peptides derived from 81 glycosidases (46 proteins from the public database and 35 uniquely from the transcriptome database) that were distributed among 13 glycoside hydrolase families were selected and quantified using multiple reaction monitoring mass spectrometry. This study showed a high glycosidase abundance and diversity in the gut contents of P. canaliculata which participate in extracellular digestion of complex dietary carbohydrates. Salivary and digestive glands were the main tissues involved in their synthesis and secretion.

Processivity and enzymatic mechanism of a multifunctional family 5 endoglucanase from Bacillus subtilis BS-5 with potential applications in the saccharification of cellulosic substrates

BACKGROUND

Presently, enzymes still constitute a major part of the cost of biofuel production from lignocellulosic biomass. Processive endoglucanases, which possess both endoglucanase and exoglucanase activity, have the potential to reduce the costs of biomass saccharification when used together with commercial cellulases. Therefore, the exploration of new processive endoglucanases has attracted much attention with a view to accelerating the industrialization of biofuels and biochemicals.

RESULTS

The endoglucanase EG5C and its truncated form EG5C-1 from Bacillus subtilis BS-5 were expressed and characterized. EG5C was a typical endoglucanase, comprised of a family 5 catalytic domain and family 3 carbohydrate-binding domain, and which had high activity toward soluble cellulosic substrates, but low activity toward insoluble cellulosic substrates. Importantly, the truncated form EG5C-1 was a processive endoglucanase that hydrolyzed not only carboxymethyl cellulose (CMC), but also insoluble cellulosic substrates. The hydrolytic activities of EG5C-1 towards CMC, phosphoric acid-swollen cellulose (PASC), p-nitrophenyl-β-d-cellobioside, filter paper and Avicel are 4170, 700, 2550, 405 and 320 U/μmol, respectively. These data demonstrated that EG5C-1 had higher activity ratio of exoglucanase to endoglucanase than other known processive endoglucanases. When PASC was degraded by EG5C-1, the ratio of soluble to insoluble reducing sugars was about 3.7 after 3 h of incubation with cellobiose and cellotriose as the main products. Importantly, EG5C-1 alone was able to hydrolyze filter paper and PASC. At 5% substrate concentration and 10 FPU/g PASC enzyme loading, the saccharification yield was 76.5% after 60 h of incubation. Replacement of a phenylalanine residue (F238) by an alanine at the entrance/exit of the substrate binding cleft significantly reduces the ability of EG5C-1 to degrade filter paper and Avicel, but this mutation has little impact on CMCase activity. The processivity of this mutant was also greatly reduced while its cellulose binding ability was markedly enhanced.

CONCLUSIONS

The processive endoglucanase EG5C-1 from B. subtilis BS-5 exhibits excellent properties that render it a suitable candidate for use in biofuel and biochemical production from lignocellulosic biomass. In addition, our studies also provide useful information for research on enzyme processivity at the molecular level.

Enhanced alkaline cellulases production by the thermohalophilic Aspergillus terreus AUMC 10138 mutated by physical and chemical mutagens using corn stover as substrate

A thermohalophilic fungus, Aspergillus terreus AUMC 10138, isolated from the Wadi El-Natrun soda lakes in northern Egypt was exposed successively to gamma and UV-radiation (physical mutagens) and ethyl methan-sulfonate (EMS; chemical mutagen) to enhance alkaline cellulase production under solid state fermentation (SSF) conditions. The effects of different carbon sources, initial moisture, incubation temperature, initial pH, incubation period, inoculum levels and different concentrations of NaCl on production of alkaline filter paper activity (FPase), carboxymethyl cellulase (CMCase) and β-glucosidase by the wild-type and mutant strains of A. terreus were evaluated under SSF. The optimum conditions for maximum production of FPase, CMCase and β-glucosidase were found to be the corn stover: moisture ratio of 1:3(w/v), temperature 45 °C, pH range, 9.0–11.0, and fermentation for 4, 4 and 7 day, respectively. Inoculum levels of 30% for β-glucosidase and 40% for FPase, CMCase gave the higher cellulase production by the wild-type and mutant strains, respectively. Higher production of all three enzymes was obtained at a 5% NaCl. Under the optimized conditions, the mutant strain A. terreus M-17 produced FPase (729 U/g), CMCase (1,783 U/g), and β-glucosidase (342 U/g), which is, 1.85, 1.97 and 2.31-fold higher than the wild-type strain. Our results confirmed that mutant strain M-17 could be a promising alkaline cellulase enzyme producer employing lignocellulosics especially corn stover.

Action modes of recombinant endocellulase, EGA, and its domains on cotton fabrics

OBJECTIVES

The action modes of an endocellulase, EGA, and its domains (CD9 and CBM3) during enzymatic treatment of cotton fabrics were investigated.

RESULTS

EGA, CD9 and CBM3 had the binding capacity to cellulose substrates, of which the filter paper was the substrate with the strongest binding capacity. Analyses of scanning electronic microscopy indicated that EGA and its catalytic domain CD9 etched the surface of cotton fabrics and broke the fibers of long chains. On the other hand, the binding domain CBM3 only resulted in swelling of cotton fibers. Both EGA and its catalytic domain CD9 had minimal effect on the weight loss of cotton fabrics, whereas the effect of EGA and CD9 on the degree of polymerization and breaking strength was significant. After 12 h enzymatic action, the values of weight loss ratio for EGA and CD9 were 2.07 and 2.21 %, respectively, meanwhile the reductions in fabric strength were 27.04 % for EGA and 17.23 % for CD9.

CONCLUSIONS

In contrast to the action of EGA and CD9, CBM3 showed no significant changes in terms of the weight loss ratio, degree of polymerization, and fabric strength.

Effect of inoculum source on the enrichment of microbial communities on two lignocellulosic bioenergy crops under thermophilic and high-solids conditions

AIMS

Culturing compost-derived microbial communities on biofuel feedstocks under industrial conditions is a technique to enrich for organisms and lignocellulolytic enzymes for bioenergy feedstock deconstruction. In this study, microbial communities from green waste compost (GWC) and grape pomace compost (GPC) were cultured on switchgrass and eucalyptus to observe the impact of inoculation on feedstock decomposition and microbial community structure.

METHODS AND RESULTS

Respiration was monitored as a measure of microbial activity, and 16S ribosomal RNA gene sequencing was used to characterize microbial community structure. The enriched community structure and respiration were influenced by the choice of feedstock, compost type, and application of thermophilic, high-solids conditions. However, the effect of compost source was significantly less than the effects of the other culture variables.

CONCLUSIONS

Although there are subtle differences in potentially lignocellulolytic taxa between GPC- and GWC-derived communities, these differences do not affect the decomposition rates for these communities on switchgrass or eucalyptus.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results are useful for designing future experiments to discover lignocellulolytic micro-organisms from compost. They suggest that such work may be better served by deemphasizing screening of compost sources and instead focusing on how compost-derived communities adapt to the feedstocks and process conditions relevant to biofuel production.

Thermostable, haloalkaline cellulase from Bacillus halodurans CAS 1 by conversion of lignocellulosic wastes

An extracellular thermostable, haloalkaline cellulase by bioconversion of lignocellulosic wastes from Bacillus halodurans CAS 1 was purified to homogeneity with recovery of 12.54% and purity fold 7.96 with the molecular weight of 44 kDa. The optimum temperature, pH and NaCl for enzyme activity was determined as 60°C, 9.0 and 30% and it retained 80% of activity even at 80°C, 12 and 35% respectively. The activity was greatly inhibited by EDTA, indicating that it was a metalloenzyme and significant inhibition by PMSF revealed that serine residue was essential for catalytic activity. The purified cellulase hydrolyzed CMC, cellobiose and xylan, but not avicel, cellulose and PNPG. Furthermore, the cellulase was highly stable in the presence of detergents and organic solvents such as acetone, n-hexane and acetonitrile. Thus, the purified cellulase from B. halodurans utilizing lignocellulosic biomass could be greatly useful to develop industrial processes.

Inhibition of cellulase-catalyzed lignocellulosic hydrolysis by iron and oxidative metal ions and complexes

Enzymatic lignocellulose hydrolysis plays a key role in microbially driven carbon cycling and energy conversion and holds promise for bio-based energy and chemical industries. Cellulases (key lignocellulose-active enzymes) are prone to interference from various noncellulosic substances (e.g., metal ions). During natural cellulolysis, these substances may arise from other microbial activities or abiotic events, and during industrial cellulolysis, they may be derived from biomass feedstocks or upstream treatments. Knowledge about cellulolysis-inhibiting reactions is of importance for the microbiology of natural biomass degradation and the development of biomass conversion technology. Different metal ions, including those native to microbial activity or employed for biomass pretreatments, are often tested for enzymatic cellulolysis. Only a few metal ions act as inhibitors of cellulases, which include ferrous and ferric ions as well as cupric ion. In this study, we showed inhibition by ferrous/ferric ions as part of a more general effect from oxidative (or redox-active) metal ions and their complexes. The correlation between inhibition and oxidation potential indicated the oxidative nature of the inhibition, and the dependence on air established the catalytic role that iron ions played in mediating the dioxygen inhibition of cellulolysis. Individual cellulases showed different susceptibilities to inhibition. It is likely that the inhibition exerted its effect more on cellulose than on cellulase. Strong iron ion chelators and polyethylene glycols could mitigate the inhibition. Potential microbiological and industrial implications of the observed effect of redox-active metal ions on enzymatic cellulolysis, as well as the prevention and mitigation of this effect in industrial biomass conversion, are discussed.

Molecular cloning, purification, and characterization of a novel, acidic, pH-stable endoglucanase from Martelella mediterranea

A novel gene encoding an endoglucanase designated Cel5D was cloned from a marine bacterium Martelella mediterranea by genomic library. The gene had a 1,113 bp opening reading frame encoding a 371-amino-acid protein with a molecular mass of 40,508 Da and containing a putative signal peptide (41 amino acids). Cel5D had low similarity (48-51% identity) with other known endoglucanases and consisted of one single catalytic domain, which belonged to the glycosyl hydrolase family 5. The maximum activity of Cel5D was observed at 60 degrees C and pH 5.0. Cel5D displayed broad pH stability within the range of pH 3.0-11.0 and retained hydrolytic activity in the presence of a wide variety of metal ions and some chemical reagents. These characteristics suggest that the enzyme has considerable potential in industrial applications.

Cel8H, a novel endoglucanase from the halophilic bacterium Halomonas sp. S66-4: molecular cloning, heterogonous expression, and biochemical characterization

A recombinant Escherichia coli clone expressing an endoglucanase was identified from a genomic library of the halophilic bacterium Halomonas sp. S66-4, and the enzyme was designated Cel8H. The cel8H gene consisted of 1,053 bp and encoded 350 amino acids sharing the highest identity of 48% to other known endoglucanases. The protein was expressed in E. coli BL21 (DE3) and purified to homogeneity. The purified recombinant enzyme had an optimal activity of 4.9 U/mg at pH 5 and 45 degrees C toward the substrate carboxymethylcellulose. It exhibited extraordinary properties which differed from endoglucanases reported previously at the point of high salt tolerance above 5 M, simultaneously with high pH stability at pH 4-12 and high temperature stability at 40-60 degrees C. Various substrate tests indicated that the enzyme hydrolyzes beta-1,4-glucosidic bonds specifically.

Improved catalytic efficiency of endo-beta-1,4-glucanase from Bacillus subtilis BME-15 by directed evolution

Bacillus subtilis endo-beta-1,4-glucanase (Cel5A) hydrolyzes cellulose by cleavage of the internal bonds in the glucose chains, producing new ends randomly. Using directed evolution techniques of error-prone polymerase chain reaction (PCR) and DNA shuffling, several Cel5A variants with improved catalytic activity had been screened from the mutant library, which contained 71,000 colonies. Compared with the wild-type enzyme, the variants (M44-11, S75 and S78) showed 2.03 to 2.68-fold increased activities toward sodium carboxymethyl cellulose (CMC), while the M44-11 also exhibited a wider pH tolerance and higher thermostability. Structural models of M44-11, S75, S78, and WT proteins revealed that most of the substitutions were not located in the strictly conserved regions, except the mutation V255A of S75, which was closed to the nucleophile Glu257 in the catalytic center of the enzyme. Moreover, V74A and D272G of M44-11, which were not located in the substrate binding sites and the catalytic center, might result in improved stability and catalytic activity. These results provided useful references for directed evolution of the enzymes that belonged to the glycoside hydrolase family 5 (GH5).

Production and characterization of cellulolytic enzymes from the thermoacidophilic fungal Aspergillus terreus M11 under solid-state cultivation of corn stover

The production of extracellular cellulases by a newly isolated thermoacidophilic fungus, Aspergillus terreus M11, on the lignocellulosic materials was studied in solid-state fermentation (SSF). The results showed that the high-level cellulase activity was produced at 45 degrees C pH 3 and moisture 80% with corn stover and 0.8% yeast extract as carbon and nitrogen sources. 581 U endoglucanase activity, 243 U filter paper activity and 128 U beta-glucosidase activity per gram of carbon source were obtained in the optimal condition. Endoglucanase and beta-glucosidase exhibited their maximum activity at pH 2 and pH 3, respectively, and both of them showed remarkable stability in the range of pH 2-5. The activities of endoglucanase and beta-glucosidase were up to the maximum at 70 degrees C and maintained about 65% and 53% of their original activities after incubation at 70 degrees C for 6h. The enzyme preparations from this strain were used to hydrolyze Avicel. Higher hydrolysis yields of Avicel were up to 63% on 5% Avicel (w/v) for 72 h with 20 U FPase/g substrate.

Catalytic and thermodynamic characterization of endoglucanase (CMCase) from Aspergillus oryzae cmc-1

Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg(-1) protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol(-1) at optimum temperature (55 degrees C), and its temperature quotient (Q (10)) was 1.0. The enzyme was stable over a pH range of 4.1-5.3 and gave maximum activity at pH 4.4. V (max) for CMC hydrolysis was 854 U mg(-1) protein and K (m) was 20 mg CMC ml(-1). The turnover (k (cat)) was 356 s(-1). The pK (a1) and pK (a2) of ionisable groups of active site controlling V (max) were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: DeltaH* = 0.59 kJ mol(-1), DeltaG* = 64.57 kJ mol(-1) and DeltaS* = -195.05 J mol(-1) K(-1), respectively. Activation energy for irreversible inactivation 'E (a(d))' of the endoglucanase was 378 kJ mol(-1), whereas enthalpy (DeltaH*), Gibbs free energy (DeltaG*) and entropy (DeltaS*) of activation at 44 degrees C were 375.36 kJ mol(-1), 111.36 kJ mol(-1) and 833.06 J mol(-1) K(-1), respectively.

Cloning of the thermostable cellulase gene from newly isolated Bacillus subtilis and its expression in Escherichia coli

A bacterial strain with high cellulase activity (0.26 U/ml culture medium) was isolated from hot spring, and classified and named as B. subtilis DR by morphological and 16SrDNA gene sequence analysis. A thermostable endocellulase, CelDR, was purified from the isolated strain. The optimum temperature of the enzyme reaction was 50 degrees C, and CelDR retained 70% of its maximum activity at 75 degrees C after incubation for 30 min. The putative gene celDR, consisting an open reading frame (ORF) of 1,524 nucleotides and encoding a protein of 508 amino acids with a molecular weight of 55 kDa, was purified from B. subtilis DR and cloned into pET-28a for expression. The cellulase production in E. coli BL21 (DE3) was enhanced to approximately three times that of the wild-type strain.

Bioconversion of lignocellulosic biomass: biochemical and molecular perspectives

In view of rising prices of crude oil due to increasing fuel demands, the need for alternative sources of bioenergy is expected to increase sharply in the coming years. Among potential alternative bioenergy resources, lignocellulosics have been identified as the prime source of biofuels and other value-added products. Lignocelluloses as agricultural, industrial and forest residuals account for the majority of the total biomass present in the world. To initiate the production of industrially important products from cellulosic biomass, bioconversion of the cellulosic components into fermentable sugars is necessary. A variety of microorganisms including bacteria and fungi may have the ability to degrade the cellulosic biomass to glucose monomers. Bacterial cellulases exist as discrete multi-enzyme complexes, called cellulosomes that consist of multiple subunits. Cellulolytic enzyme systems from the filamentous fungi, especially Trichoderma reesei, contain two exoglucanases or cellobiohydrolases (CBH1 and CBH2), at least four endoglucanases (EG1, EG2, EG3, EG5), and one beta-glucosidase. These enzymes act synergistically to catalyse the hydrolysis of cellulose. Different physical parameters such as pH, temperature, adsorption, chemical factors like nitrogen, phosphorus, presence of phenolic compounds and other inhibitors can critically influence the bioconversion of lignocellulose. The production of cellulases by microbial cells is governed by genetic and biochemical controls including induction, catabolite repression, or end product inhibition. Several efforts have been made to increase the production of cellulases through strain improvement by mutagenesis. Various physical and chemical methods have been used to develop bacterial and fungal strains producing higher amounts of cellulase, all with limited success. Cellulosic bioconversion is a complex process and requires the synergistic action of the three enzymatic components consisting of endoglucanases, exoglucanases and beta-glucosidases. The co-cultivation of microbes in fermentation can increase the quantity of the desirable components of the cellulase complex. An understanding of the molecular mechanism leading to biodegradation of lignocelluloses and the development of the bioprocessing potential of cellulolytic microorganisms might effectively be accomplished with recombinant DNA technology. For instance, cloning and sequencing of the various cellulolytic genes could economize the cellulase production process. Apart from that, metabolic engineering and genomics approaches have great potential for enhancing our understanding of the molecular mechanism of bioconversion of lignocelluloses to value added economically significant products in the future.

Purification and characterization of cellulase produced by Bacillus amyoliquefaciens DL-3 utilizing rice hull

A microorganism hydrolyzing rice hull was isolated from soil and identified as Bacillus amyloliquefaciens by analysis of 16S rDNA and partial sequences of the gyrA gene, and named as B. amyloliquefaciens DL-3. With the analysis of SDS-PAGE, the molecular weight of the purified cellulase was estimated to be 54kDa. The purified cellulase hydrolyzed avicel, caboxymethylcellulose (CMC), cellobiose, beta-glucan and xylan, but not p-Nitrophenyl-beta-D-glucopyranoside (PNPG). Optimum temperature and pH for the CMCase activity of the purified cellulase were found to be 50 degrees C and pH 7.0, respectively. The CMCase activity was inhibited by some metal ions, N-bromosuccinimide and EDTA in the order of Hg(2+)>EDTA>Mn(2+)>N-bromosuccinimide>Ni(2+)>Pb(2+)>Sr(2+)>Co(2+)>K(+). The open reading frame of the cellulase from B. amyloliquefaciens DL-3 was found to encode a protein of 499 amino acids. The deduced amino acid sequence of the cellulase from B. amyloliquefaciens DL-3 showed high identity to cellulases from other Bacillus species, a modular structure containing a catalytic domain of the glycoside hydrolase family 5 (GH5), and a cellulose-binding module type 3 (CBM3).

Molecular and biochemical characterization of Ba-EGA, a cellulase secreted by Bacillus sp. AC-1 from Ampullaria crosseans

A novel gene (Ba-ega) of Bacillus sp. AC-1, encoding an endoglucanase (Ba-EGA), was cloned and expressed in Escherichia coli. Ba-ega, containing a 1,980-bp open reading frame (ORF), encoded a protein of 659 amino acids and had a molecular mass of 74.87 kDa. Ba-EGA was a modular enzyme composed of a family-9 glycosyl hydrolase catalytic module (CM9) and a family-3 carbohydrate-binding module (CBM3). To investigate the functions of the CBM3 and CM9, a number of truncated derivatives of Ba-EGA were constructed, and all were active. The catalytic module (rCM9) alone was less stable at high temperature than the recombinant Ba-EGA (rBa-EGA). The temperature stability for the complex of rCM9 and rCBM3 was still lower than rBa-EGA, but higher than rCM9 alone. These observations indicated the existence of a non-covalent interaction between CM9 and CBM3 that might strengthen the stability of CM9. However, this interaction is not strong enough to mimic the protective effect of the CBM in the wild-type enzyme.