Characterization of a β-glucosidase from Paenibacillus species and its application for succinic acid production from sugarcane bagasse hydrolysate

Biodetoxification of Lignocellulose Hydrolysate for Direct Use in Succinic Acid Production

The pretreatment of lignocellulosic biomass with acid generates phenolic and furanyl compounds that function as toxins by inhibiting microbial growth and metabolism. Therefore, it is necessary to detoxify acid-pretreated lignocellulosic biomass for better utilization. Among the various detoxification methods that are available, biodetoxification offers advantages that include mild reaction conditions and low energy consumption. In this study, a newly isolated Rhodococcus aetherivorans strain, N1, was found to effectively degrade various lignin-derived aromatic compounds, such as p-coumarate, ferulate, syringaldehyde, furfural, and 5-hydroxymethylfurfural. Furthermore, the metabolic pathway and genes responsible for this degradation were also identified. In addition, the overexpression of a demethylase (DesA) and 3,4-dioxygenase (DesZ) in strain N1 generated a recombinant strain, N1-S, which showed an enhanced ability to degrade syringaldehyde and 80.5% furfural, 50.7% 5-hydroxymethylfurfural, and 71.5% phenolic compounds in corn cob hydrolysate. The resulting detoxified hydrolysate was used directly as a feedstock for succinate production by Escherichia coli suc260. This afforded 35.3 g/l succinate, which was 6.5 times greater than the concentration afforded when nondetoxified hydrolysate was used. Overall, the results of this study demonstrate that strain N1-S is a valuable microbe for the biodetoxification of lignocellulosic biomass.

Exploring the diversity of β-glucosidase: Classification, catalytic mechanism, molecular characteristics, kinetic models, and applications

High-value chemicals and energy-related products can be produced from biomass. Biorefinery technology offers a sustainable and cost-effective method for this high-value conversion. β-glucosidase is one of the key enzymes in biorefinery processes, catalyzing the production of glucose from aryl-glycosides and cello-oligosaccharides via the hydrolysis of β-glycosidic bonds. Although β-glucosidase plays a critical catalytic role in the utilization of cellulosic biomass, its efficacy is often limited by substrate or product inhibitions, low thermostability, and/or insufficient catalytic activity. To provide a detailed overview of β-glucosidases and their benefits in certain desired applications, we collected and summarized extensive information from literature and public databases, covering β-glucosidases in different glycosidase hydrolase families and biological kingdoms. These β-glucosidases show differences in amino acid sequence, which are translated into varying degrees of the molecular properties critical in enzymatic applications. This review describes studies on the diversity of β-glucosidases related to the classification, catalytic mechanisms, key molecular characteristics, kinetics models, and applications, and highlights several β-glucosidases displaying high stability, activity, and resistance to glucose inhibition suitable for desired biotechnological applications.

Screening of bioflocculant and cellulase-producing bacteria strains for biofloc culture systems with fiber-rich carbon source

The biofloc technology (BFT) system has been widely applied in the shrimp and fish culture industry for its advantages in water-saving, growth improvement, and water quality purification. However, The BFT system usually takes a long time to establish, and the extra carbon source input increases the maintenance cost of the system. In this study, we aimed to develop a low-cost and high-efficient BFT system for Litopenaeus vannamei by applying bacteria that could promote the formation of BFT and utilize cheap carbon sources. Three bioflocculant-producing bacteria strains (M13, M15, and M17) have been screened from a cellulolytic strain collection. All three strains have been identified as Bacillus spp. and can use sugarcane bagasse (SB) as a carbon source, which is a cheap byproduct of the sucrose industry in the tropic area of China. Compared to sucrose, the addition of SB and the three strains could improve the biofloc formation rate, biofloc size distribution, ammonia removal rate, and the growth performance of the shrimps. These results suggest that the bioflocculant and cellulase-producing bacteria strains could promote the biofloc formation and the growth of shrimps by using SB as an economic substitute carbon source in the BFT shrimp culture system.

Technological advancements in valorization of second generation (2G) feedstocks for bio-based succinic acid production

Succinic acid (SA) is used as a commodity chemical and as a precursor in chemical industry to produce other derivatives such as 1,4-butaneidol, tetrahydrofuran, fumaric acid, and bio-polyesters. The production of bio-based SA from renewable feedstocks has always been in the limelight owing to the advantages of renewability, abundance and reducing climate change by CO₂ capture. Considering this, the current review focuses on various 2G feedstocks such as lignocellulosic biomass, crude glycerol, and food waste for cost-effective SA production. It also highlights the importance of producing SA via separate enzymatic hydrolysis and fermentation, simultaneous saccharification and fermentation, and consolidated bioprocessing. Furthermore, recent advances in genetic engineering, and downstream SA processing are thoroughly discussed. It also elaborates on the techno-economic analysis and life cycle assessment (LCA) studies carried out to understand the economics and environmental effects of bio-based SA synthesis.

Tropical Cellulolytic Bacteria: Potential Utilization of Sugarcane Bagasse as Low-Cost Carbon Source in Aquaculture

Sugarcane bagasse (SB), as a major by-product of sugarcane, is one of the most abundant organic matter and characterized by cheap and easily available carbon source in Hainan Island, China. The objective of this study was to isolate tropical cellulolytic bacteria from Hainan Island and demonstrate their prospects of utilization of SB as a low-cost carbon source to greatly reduce the cost of aquaculture. A total of 97 cellulolytic marine bacteria were isolated, of which, 58 cellulolytic marine bacteria displayed the hydrolysis capacity (HC) of more than 1, while 28 cellulolytic marine bacteria displayed more than 2. Of the 28 tropical cellulolytic bacterial strains with HC more than 2, Microbulbifer sp. CFW-C18 and Vibrio sp. MW-M19 exhibited excellent SB decomposition in a small-scale laboratory simulation of shrimp aquaculture, up to 75.31 and 74.35%, respectively, and both of them were safe for shrimps. Meanwhile, both of CFW-C18 and MW-M19 besides displaying low multiple antibiotic resistance (MAR) index, also increased the C/N ratio (CFW-C18: C/N ratio of 14.34; MW-M19: C/N ratio of 14.75) of the small-scale laboratory simulation of shrimp aquaculture by decreasing the nitrogen content after a supplement of SB for 15 days. More importantly, CFW-C18 and MW-M19 displayed a relatively low MAR index, 0.47 and 0.1, respectively, especially MW-M19, with the lowest MAR index (0.1), which was resistant to only three antibiotics, streptomycin, amikacin, and levofloxacin, indicating that this strain was safe and non-drug resistance for further use. Overall, tropical cellulolytic bacteria isolated from Hainan Island, especially CFW-C18 and MW-M19, will provide the proficient candidates as probiotics for further construction of the recirculating aquaculture system based on the supplement of low-cost external carbon source—SB.

Directional bioconversion and optimization of stevioside into rubusoside by Lelliottia sp. LST-1

AIMS

The present study aimed to specifically transform stevioside (ST) into rubusoside (RS) through bioconversion with high efficiency, seeking to endow steviol glycosides (SGs) with subtle flavours for commercial acceptability.

METHODS AND RESULTS

An endophytic bacterium named Lelliottia LST-1 was screened and confirmed to specifically convert ST into RS, reaching a conversion rate of 75.4% after response surface optimization. Phylogenetic analysis combined with complete genome sequencing demonstrated that LST-1 was also presumed to be a new species. To further explore the principle and process of biological transformation, the potential beta-glucosidases GH3-1, GH3-2, GH3-3 and GH3-4 were expressed, purified and reacted with SGs. High-performance liquid chromatography revealed that all enzymes hydrolysed ST and generated RS, but substrate specificity analysis indicated that GH3-2 had the highest substrate specificity towards STs and the highest enzyme activity.

CONCLUSION

The potential β-glucosidase GH3-2 in Lelliottia sp. LST-1 was found to specifically and efficiently convert ST to RS.

SIGNIFICANCE AND IMPACT OF STUDY

The efficient biotransformation of ST into RS will be beneficial to its large-scale production and extensive application in the food and pharmaceutical industries.

Molecular modeling, docking and simulation dynamics of β-glucosidase reveals high-efficiency, thermo-stable, glucose tolerant enzyme in Paenibacillus lautus BHU3 strain

The enzyme β-glucosidase mediates the rate limiting step of conversion of cellobiose to glucose and thus plays a vital role in the process of cellulose degradation. The present study deals with analysis of the effective novel strain of Paenibacillus lautus BHU3 for identifying high-efficiency thermostable, glucose tolerant β-glucosidases. Seven counterparts with elevated T_m values ranging from 64.6 to 75.8 °C with high thermo-stability, were revealed through this analysis. The blind molecular docking of the model enzymes structures with cellobiose and pNPG gave high negative interaction energies ranging from -11.33 to -13.29 and -6.43 to -9.054 (kcal mol^-1), respectively. The enzyme WP_096774744.1 effectively formed 5 hydrogen bonds with the highest interaction energy (-13.29 kcal mol^-1) with cellobiose at its catalytic site. Molecular dynamics simulation analysis performed for the WP_096774744.1-pNPG complex predicted Glu5, Arg7, Lue68, Gly69 and Phe325 as the major contributing residues for accomplishing hydrolysis of β-1-4-linkage. Further, the molecular docking of WP_096774744.1 enzyme with glucose revealed a distinct glucose-binding site distant from the substrate-binding site, thus confirming the deficient competitive inhibition by glucose. Hence, WP_096774744.1 β-glucosidase appears to be an efficient enzyme with enhanced activity to biodegrade the cellulosic materials and highly relevant for waste management and various industrial applications.

Functional genomics assessment of lytic polysaccharide mono-oxygenase with glycoside hydrolases in Paenibacillus dendritiformis CRN18

Recently discovered Lytic Polysaccharide Mono-Oxygenase (LPMO) enhances the enzymatic deconstruction of complex polysaccharide by oxidation. The present study demonstrates the agricultural waste hydrolyzing capabilities of Paenibacillus dendritiformis CRN18, which exhibits the enzyme activity of exo-glucanase, β-glucosidase, β-glucuronidase, endo-1, 4 β-xylanases, arabinosidase, and α-galactosidase as 0.1U/ml, 0.3U/ml, 0.09U/ml, 0.1U/ml, 0.05U/ml, and 0.41U/ml, respectively. The genome analysis of strain reveals the presence of four LPMO genes, along with lignocellulolytic genes. The gene structure of LPMO and its phylogenetic analysis shows the evolutionary relatedness with the Bacillus LPMO gene. Gene position of LPMOs in the genome of strains shows the close association of two LPMOs with chitin active enzyme GH18, and the other two are associated with hemicellulases (GH39, GH23). Protein-protein interaction and gene networking of LPMO sheds light on the co-occurrence, neighborhood, and interaction of LPMOs with chitinase and xylanase enzymes. Structural prediction of LPMOs unravels the information of the LPMO's binding site. Although the LPMO has been explored for its oxidative mechanism, a little light has been shed on its gene structure. This study provides insights into the LPMO gene structure in P. dendritiformis CRN18 and its potential in lignocellulose hydrolysis.

Enhancement of high-solids enzymatic hydrolysis efficiency of alkali pretreated sugarcane bagasse at low cellulase dosage by fed-batch strategy based on optimized accessory enzymes and additives

Obtaining higher amount of final sugars with low cellulase dosage has great economic benefits for the industrial biorefinery of lignocellulosic biomass. The optimization of accessory enzymes and additives were performed using single factor and orthogonal experiment firstly, after that, fed-batch strategy was applied to enhance the high-solids enzymatic hydrolysis efficiency of alkali pretreated sugarcane bagasse (SCB). A novel enzymatic hydrolysis procedure with 22% (w/v) substrate content and cellulase dosage of only 4 FPU/g dry biomass (DM) was developed, after digested for 48 h, the achieved glucose titer, yield and productivity were 122 g/L, 80% and 2.54 g L^-1 h^-1, respectively. Results obtained in this study indicated a potential finding for the industrial application of lignocellulosic biomass.

A new enzymatic method assessing the impact of wastewater treatment plant effluents on the assimilative capacity of small rivers

Microorganisms play an important role in maintaining a good water quality in rivers by degrading organic material, including toxic substances. In the present study, we analyzed the potential impact of municipal wastewater treatment plant (WWTP) effluents as a major stress factor on the assimilative capacity of small rivers. It was the aim to develop a new bioassay for assessing such impacts in the receiving rivers by measuring the activity of extracellular enzymes (exoenzymes) in bacteria. Therefore, we established a specific in-vitro assay to detect inhibitory effects of solid phase-enriched water samples on β-glucosidase (BGL) activity of the actinobacterium Cellulomonas uda as a proxy for the microbial decomposition of organic substances and thus for the assimilative capacity of surface waters. We found significant reductions of BGL activity in the WWTP effluents and in the receiving waters directly downstream as well as a relative quick recovery over the further course of the water bodies. The new bioassay offers a promising tool for the assessment of the assimilative capacity in surface waters and a potential impact of WWTP effluents on this key ecosystem function. Abbreviations WWTP wastewater treatment plant BGL β-glucosidase EU-WFD European Water Framework Directive FAU Formazin Attenuation Units PE population equivalents REF relative enrichment factor; SPE solid phase extraction MTBE methyl-tert-buthyl-ether DMSO dimethyl-sulfoxide NPG 4-nitrophenol-β-d-glucopyranoside DOC dissolved organic carbon.