New glucosidase activities identified by functional screening of a genomic DNA library from the gut microbiota of the termite Reticulitermes santonensis

Multipartite symbioses in fungus-growing termites (Blattodea: Termitidae, Macrotermitinae) for the degradation of lignocellulose

Fungus-growing termites are among the most successful herbivorous animals and improve crop productivity and soil fertility. A range of symbiotic organisms can be found inside their nests. However, interactions of termites with these symbionts are poorly understood. This review provides detailed information on the role of multipartite symbioses (between termitophiles, termites, fungi, and bacteria) in fungus-growing termites for lignocellulose degradation. The specific functions of each component in the symbiotic system are also discussed. Based on previous studies, we argue that the enzymatic contribution from the host, fungus, and bacteria greatly facilitates the decomposition of complex polysaccharide plant materials. The host-termitophile interaction protects the termite nest from natural enemies and maintains the stability of the microenvironment inside the colony.

Bioprospecting of novel thermostable β-glucosidase from Bacillus subtilis RA10 and its application in biomass hydrolysis

BACKGROUND

Saccharification is the most crucial and cost-intensive process in second generation biofuel production. The deficiency of β-glucosidase in commercial enzyme leads to incomplete biomass hydrolysis. The decomposition of biomass at high temperature environments leads us to isolate thermotolerant microbes with β-glucosidase production potential.

RESULTS

A total of 11 isolates were obtained from compost and cow dung samples that were able to grow at 50 °C. On the basis of qualitative and quantitative estimation of β-glucosidase enzyme production, Bacillus subtilis RA10 was selected for further studies. The medium components and growth conditions were optimized and β-glucosidase enzyme production was enhanced up to 19.8-fold. The β-glucosidase from B. subtilis RA10 retained 78% of activity at 80 °C temperature and 68.32% of enzyme activity was stable even at 50 °C after 48 h of incubation. The supplementation of β-glucosidase from B. subtilis RA10 into commercial cellulase enzyme resulted in 1.34-fold higher glucose release. Furthermore, β-glucosidase was also functionally elucidated by cloning and overexpression of full length GH1 family β-glucosidase gene from B. subtilis RA10. The purified protein was characterized as thermostable β-glucosidase enzyme.

CONCLUSIONS

The thermostable β-glucosidase enzyme from B. subtilis RA10 would facilitate efficient saccharification of cellulosic biomass into fermentable sugar. Consequently, after saccharification, thermostable β-glucosidase enzyme would be recovered and reused to reduce the cost of overall bioethanol production process.

Catalytic properties, functional attributes and industrial applications of β-glucosidases

β-Glucosidases are diverse group of enzymes with great functional importance to biological systems. These are grouped in multiple glycoside hydrolase families based on their catalytic and sequence characteristics. Most studies carried out on β-glucosidases are focused on their industrial applications rather than their endogenous function in the target organisms. β-Glucosidases performed many functions in bacteria as they are components of large complexes called cellulosomes and are responsible for the hydrolysis of short chain oligosaccharides and cellobiose. In plants, β-glucosidases are involved in processes like formation of required intermediates for cell wall lignification, degradation of endosperm’s cell wall during germination and in plant defense against biotic stresses. Mammalian β-glucosidases are thought to play roles in metabolism of glycolipids and dietary glucosides, and signaling functions. These enzymes have diverse biotechnological applications in food, surfactant, biofuel, and agricultural industries. The search for novel and improved β-glucosidase is still continued to fulfills demand of an industrially suitable enzyme. In this review, a comprehensive overview on detailed functional roles of β-glucosidases in different organisms, their industrial applications, and recent cloning and expression studies with biochemical characterization of such enzymes is presented for the better understanding and efficient use of diverse β-glucosidases.

Two-step statistical optimization for cold active β-glucosidase production from Pseudomonas lutea BG8 and its application for improving saccharification of paddy straw

β-Glucosidase is an essential part of cellulase enzyme system for efficient and complete hydrolysis of biomass. Psychrotolerant Pseudomonas lutea BG8 produced β-glucosidase with lower temperature optima and hence can play important role in bringing down the energy requirement for bioethanol production. To enhance β-glucosidase production, two statistical tools: Taguchi and Box-Behnken designs were applied to reveal the most influential factors and their respective concentration for maximum production of β-glucosidase under submerged fermentation. The optimal medium composition for maximum β-glucosidase production were 2.99% (w/v) bagasse, 0.33% (w/v) yeast extract, 0.38% (w/v) Triton X-100, 0.39% (w/v) NaNO₃ , and pH 8.0 at temperature 30 °C. Under optimized conditions, β-glucosidase production increased up to 9.12-fold (17.52 ± 0.24 IU/g) in shake flask. Large-scale production in 7-L stirred tank bioreactor resulted in higher β-glucosidase production (23.29 ± 0.23 IU/g) within 80 H of incubation, which was 1.34-fold higher than shake flask studies. Commercial cellulase (Celluclast^® 1.5L) when supplemented with this crude β-glucosidase resulted in improved sugar release (548.4 ± 2.76 mg/gds) from paddy straw at comparatively low temperature (40 °C) of saccharification. P. lutea BG8 therefore showed great potential for cold active β-glucosidase production and can be used as accessory enzyme along with commercial cellulase to improve saccharification efficiency.

Omic research in termites: an overview and a roadmap

Many recent breakthroughs in our understanding of termite biology have been facilitated by "omics" research. Omic science seeks to collectively catalog, quantify, and characterize pools of biological molecules that translate into structure, function, and life processes of an organism. Biological molecules in this context include genomic DNA, messenger RNA, proteins, and other biochemicals. Other permutations of omics that apply to termites include sociogenomics, which seeks to define social life in molecular terms (e.g., behavior, sociality, physiology, symbiosis, etc.) and digestomics, which seeks to define the collective pool of host and symbiont genes that collaborate to achieve high-efficiency lignocellulose digestion in the termite gut. This review covers a wide spectrum of termite omic studies from the past 15 years. Topics covered include a summary of terminology, the various kinds of omic efforts that have been undertaken, what has been revealed, and to a degree, what the results mean. Although recent omic efforts have contributed to a better understanding of many facets of termite and symbiont biology, and have created important new resources for many species, significant knowledge gaps still remain. Crossing these gaps can best be done by applying new omic resources within multi-dimensional (i.e., functional, translational, and applied) research programs.

Identification and characterization of a halotolerant, cold-active marine endo-β-1,4-glucanase by using functional metagenomics of seaweed-associated microbiota

A metagenomic library was constructed from microorganisms associated with the brown alga Ascophyllum nodosum. Functional screening of this library revealed 13 novel putative esterase loci and two glycoside hydrolase loci. Sequence and gene cluster analysis showed the wide diversity of the identified enzymes and gave an idea of the microbial populations present during the sample collection period. Lastly, an endo-β-1,4-glucanase having less than 50% identity to sequences of known cellulases was purified and partially characterized, showing activity at low temperature and after prolonged incubation in concentrated salt solutions.

New carbohydrate-active enzymes identified by screening two metagenomic libraries derived from the soil of a winter wheat field

AIMS

Soils are rich, diversified environments where β-glucosidases abound because of their importance in organic matter degradation. The aim of this work was to discover new β-glucosidases by constructing two metagenomic DNA libraries from soil samples collected in winter and spring from a field of winter wheat.

METHODS AND RESULTS

Both libraries were screened on esculin-supplemented medium so as to isolate candidates showing β-glucosidase activity. Candidate analysis revealed seven putative β-glycosidases and two putative glycosyltransferases, displaying 25 to 82% identity to known enzymes. The putative β-glycosidases belong to families GH1, GH3 and GH20 and the two putative glycosyltransferases, probably, to new families. In characterization tests performed on bacteria in suspension or spread on agar plates, some candidates appeared to hydrolyse several natural and synthetic substrates. These tests also highlighted interesting industrial characteristics, such as the activity of four β-glycosidases under alkaline conditions and the esculin-hydrolysing activity of a β-glucosidase candidate in the presence of glucose.

CONCLUSIONS

Seven putative β-glycosidases and two putative glycosyltransferases were found by functional screening of two metagenomic DNA libraries derived from agricultural soil.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has identified β-glycosidases and putative glycosyltransferases that have or may have interesting industrial characteristics.

Host-specific assemblages typify gut microbial communities of related insect species

Mutualisms between microbes and insects are ubiquitous and facilitate exploitation of various trophic niches by host insects. Dictyopterans (mantids, cockroaches and termites) exhibit trophisms that range from omnivory to strict wood-feeding and maintain beneficial symbioses with the obligate endosymbiont, Blattabacterium, and/or diverse gut microbiomes that include cellulolytic and diazotrophic microbes. While Blattabacterium in omnivorous Periplaneta is fully capable of provisioning essential amino acids, in wood-feeding dictyopterans it has lost many genes for their biosynthesis (Mastotermes and Cryptocercus) or is completely absent (Heterotermes). The conspicuous functional degradation and absence of Blattabacterium in most strict wood-feeding dictyopteran insects suggest that alternative means of acquiring nutrients limited in their diet are being employed. A 16S rRNA gene amplicon resequencing approach was used to deeply sample the composition and diversity of gut communities in related dictyopteran insects to explore the possibility of shifts in symbiont allegiances during termite and cockroach evolution. The gut microbiome of Periplaneta, which has a fully functional Blattabacterium, exhibited the greatest within-sample operational taxonomic unit (OTU) diversity and abundance variability than those of Mastotermes and Cryptocercus, whose Blattabacterium have shrunken genomes and reduced nutrient provisioning capabilities. Heterotermes lacks Blattabacterium and a single OTU that was 95% identical to a Bacteroidia-assigned diazotrophic endosymbiont of an anaerobic cellulolytic protist termite gut inhabitant samples consistently dominates its gut microbiome. Many host-specific OTUs were identified in all host genera, some of which had not been previously detected, indicating that deep sampling by pyrotag sequencing has revealed new taxa that remain to be functionally characterized. Further analysis is required to uncover how consistently detected taxa in the cockroach and termite gut microbiomes, as well as the total community, contribute to host diet choice and impact the fate of Blattabacterium in dictyopterans.

Two promising alkaline β-glucosidases isolated by functional metagenomics from agricultural soil, including one showing high tolerance towards harsh detergents, oxidants and glucose

New β-glucosidase activities were identified by screening metagenomic libraries constructed with DNA isolated from the topsoil of a winter wheat field. Two of the corresponding proteins, displaying an unusual preference for alkaline conditions, were selected for purification by Ni-NTA chromatography. AS-Esc6, a 762-amino-acid enzyme belonging to glycoside hydrolase family 3, proved to be a mesophilic aryl-β-glucosidase with maximal activity around pH 8 and 40 °C. A similar pH optimum was found for AS-Esc10, a 475-amino-acid GH1-family enzyme, but this enzyme remained significantly active across a wider pH range and was also markedly more stable than AS-Esc6 at pH greater than 10. AS-Esc10 was found to degrade cellobiose and diverse aryl glycosides, with an optimal temperature of 60 °C and good stability up to 50 °C. Unlike AS-Esc6, which showed a classically low inhibitory constant for glucose (14 mM), AS-Esc10 showed enhanced activity in the presence of molar concentrations of glucose. AS-Esc10 was highly tolerant to hydrogen peroxide and also to sodium dodecyl sulfate, this being indicative of kinetic stability. This unique combination of properties makes AS-Esc10 a particularly promising candidate whose potential in biotechnological applications is worth exploring further.

16S-rRNA-based analysis of bacterial diversity in the gut of fungus-cultivating termites (Microtermes and Odontotermes species)

The interaction between termites and their gut symbionts has continued to attract the curiosity of researchers over time. The aim of this study was to characterize and compare the bacterial diversity and community structure in the guts of three termites (Odontotermes somaliensis, Odontotermes sp. and Microtermes sp.) using 16S rRNA gene sequencing of clone libraries. Clone libraries were screened by restriction fragment length polymorphism and representative clones from O. somaliensis (100 out of 330 clones), Odontotermes sp. (100 out of 359 clones) and Microtermes sp. (96 out 336 clones) were sequenced. Phylogenetic analysis indicated seven bacterial phyla were represented: Bacteroidetes, Spirochaetes, Firmicutes, Proteobacteria, Synergistetes, Planctomycetes and Actinobacteria. Sequences representing the phylum Bacteroidetes (>60 %) were the most abundant group in Odontotermes while those of Spirochaetes (29 %) and Firmicutes (23 %) were the abundant groups in Microtermes. The gut bacterial community structure within the two Odontotermes species investigated here was almost identical at the phylum level, but the Microtermes sp. had a unique bacterial community structure. Bacterial diversity was higher in Odontotermes than in Microtermes. The affiliation and clustering of the sequences, often with those from other termites' guts, indicate a majority of the gut bacteria are autochthonous having mutualistic relationships with their hosts. The findings underscore the presence of termite-specific bacterial lineages, the majority of which are still uncultured.

Activation of a casB gene encoding β-glucosidase of Pectobacterium carotovorum subsp. carotovorum LY34

Two cas genes were isolated from Pectobacterium carotovorum subsp. carotovorum LY34 (Pcc LY34). Sequence analysis of the 4873 bp cloned DNA fragment (accession number AY866383) revealed two open reading frames (casF and casB) that are predicted to encode 658 and 467 amino acid proteins, respectively. The CasF protein is similar to other PTS enzyme II components. casB encodes β-glucosidase, a member of the glycosyl hydrolase family 1. An inverted repeat sequence was identified in the casB promoter region, and was hypothesized to have a negative effect on casB transcription. Replacement of the casB promoter of Pcc LY34 with the bglB promoter activated the casB gene, consistent with the repeats inhibiting expression of casB. Purified CasB enzyme was estimated to be 53,000 Da by SDS-PAGE, and hydrolyzed salicin, arbutin, pNPG, and MUG. CasB exhibited maximal activity toward pNPG at pH 7.0 and 40 °C, and Mg(2+) is essential for its activity. Two conserved glutamate residues (Glu(177) and Glu(366)) were shown to be important for CasB activity.

A pharm-ecological perspective of terrestrial and aquatic plant-herbivore interactions

We describe some recent themes in the nutritional and chemical ecology of herbivores and the importance of a broad pharmacological view of plant nutrients and chemical defenses that we integrate as "Pharm-ecology". The central role that dose, concentration, and response to plant components (nutrients and secondary metabolites) play in herbivore foraging behavior argues for broader application of approaches derived from pharmacology to both terrestrial and aquatic plant-herbivore systems. We describe how concepts of pharmacokinetics and pharmacodynamics are used to better understand the foraging phenotype of herbivores relative to nutrient and secondary metabolites in food. Implementing these concepts into the field remains a challenge, but new modeling approaches that emphasize tradeoffs and the properties of individual animals show promise. Throughout, we highlight similarities and differences between the historic and future applications of pharm-ecological concepts in understanding the ecology and evolution of terrestrial and aquatic interactions between herbivores and plants. We offer several pharm-ecology related questions and hypotheses that could strengthen our understanding of the nutritional and chemical factors that modulate foraging behavior of herbivores across terrestrial and aquatic systems.