Prospection and Evaluation of (Hemi) Cellulolytic Enzymes Using Untreated and Pretreated Biomasses in Two Argentinean Native Termites

Exploring the cellulolytic activity of environmental mycobacteria

Although studies on non-tuberculous mycobacteria have increased in recent years because they cause a considerable proportion of infections, their cellulolytic system is still poorly studied. This study presents a characterization of the cellulolytic activities of environmental mycobacterial isolates derived from soil and water samples from the central region of Argentina, aimed to evaluate the conservation of the mechanism for the degradation of cellulose in this group of bacteria. The molecular and genomic identification revealed identity with Mycolicibacterium septicum. The endoglucanase and total cellulase activities were assessed both qualitatively and quantitatively and the optimal enzymatic conditions were characterized. A specific protein of around 56 kDa with cellulolytic activity was detected in a zymogram. Protein sequences possibly arising from a cellulase were identified by mass spectrometry-based shotgun proteomics. Results showed that M. septicum encodes for cellulose- and hemicellulose-related degrading enzymes, including at least an active β-1,4 endoglucanase enzyme that could be useful to improve its survival in the environment. Given the important health issues related to mycobacteria, the results of the present study may contribute to the knowledge of their cellulolytic system, which could be important for their ability to survive in many different types of environments.

Disturbance-diversity relationships of microbial communities change based on growth substrate

Disturbance events can impact ecological community dynamics. Understanding how communities respond to disturbances and how those responses can vary is a challenge in microbial ecology. In this study, we grew a previously enriched specialized microbial community on either cellulose or glucose as a sole carbon source and subjected them to one of five different disturbance regimes of varying frequencies ranging from low to high. Using 16S rRNA gene amplicon sequencing, we show that the community structure is largely driven by substrate, but disturbance frequency affects community composition and successional dynamics. When grown on cellulose, bacteria in the genera Cellvibrio, Lacunisphaera, and Asticcacaulis are the most abundant microbes. However, Lacunisphaera is only abundant in the lower disturbance frequency treatments, while Asticcacaulis is more abundant in the highest disturbance frequency treatment. When grown on glucose, the most abundant microbes are two Pseudomonas sequence variants and a Cohnella sequence variant that is only abundant in the highest disturbance frequency treatment. Communities grown on cellulose exhibited a greater range of diversity (1.95-7.33 Hill 1 diversity) that peaks at the intermediate disturbance frequency treatment or one disturbance every 3 days. Communities grown on glucose, however, ranged from 1.63 to 5.19 Hill 1 diversity with peak diversity at the greatest disturbance frequency treatment. These results demonstrate that the dynamics of a microbial community can vary depending on substrate and the disturbance frequency and may potentially explain the variety of diversity-disturbance relationships observed in microbial systems.IMPORTANCEA generalizable diversity-disturbance relationship (DDR) of microbial communities remains a contentious topic. Various microbial systems have different DDRs. Rather than finding support or refuting specific DDRs, we investigated the underlying factors that lead to different DDRs. In this study, we measured a cellulose-enriched microbial community's response to a range of disturbance frequencies from high to low, across two different substrates: cellulose and glucose. We demonstrate that the community displays a unimodal DDR when grown on cellulose and a monotonically increasing DDR when grown on glucose. Our findings suggest that the same community can display different DDRs. These results suggest that the range of DDRs we observe across different microbial systems may be due to the nutritional resources microbial communities can access and the interactions between bacteria and their environment.

Disturbance-Diversity Relationships of Microbial Communities Change Based on Growth Substrate

Disturbance events can impact ecological community dynamics. Understanding how communities respond to disturbances, and how those responses can vary, is a challenge in microbial ecology. In this study, we grew a previously enriched specialized microbial community on either cellulose or glucose as a sole carbon source, and subjected them to one of five different disturbance regimes of varying frequencies ranging from low to high. Using 16S rRNA gene amplicon sequencing, we show that community structure is largely driven by substrate, but disturbance frequency affects community composition and successional dynamics. When grown on cellulose, bacteria in the genera Cellvibrio, Lacunisphaera, and Asticaccacaulis are the most abundant microbes. However, Lacunisphaera is only abundant in the lower disturbance frequency treatments, while Asticaccaulis is more abundant in the highest disturbance frequency treatment. When grown on glucose, the most abundant microbes are two Pseudomonas sequence variants, and a Cohnella sequence variant that is only abundant in the highest disturbance frequency treatment. Communities grown on cellulose exhibited a greater range of diversity (0.67-1.99 Shannon diversity and 1.38-5.25 Inverse Simpson diversity) that peak at the intermediate disturbance frequency treatment, or 1 disturbance every 3 days. Communities grown on glucose, however, ranged from 0.49-1.43 Shannon diversity and 1.37- 3.52 Inverse Simpson with peak diversity at the greatest disturbance frequency treatment. These results demonstrate that the dynamics of a microbial community can vary depending on substrate and the disturbance frequency, and may potentially explain the variety of diversity-disturbance relationships observed in microbial ecosystems.

CAZyme from gut microbiome for efficient lignocellulose degradation and biofuel production

Over-exploitation and energy security concerns of the diminishing fossil fuels is a challenge to the present global economy. Further, the negative impact of greenhouse gases released using conventional fuels has led to the need for searching for alternative biofuel sources with biomass in the form of lignocellulose coming up as among the potent candidates. The entrapped carbon source of the lignocellulose has multiple applications other than biofuel generation under the biorefinery approach. However, the major bottleneck in using lignocellulose for biofuel production is its recalcitrant nature. Carbohydrate Active Enzymes (CAZymes) are enzymes that are employed for the disintegration and consumption of lignocellulose biomass as the carbon source for the production of biofuels and bio-derivatives. However, the cost of enzyme production and their stability and catalytic efficiency under stressed conditions is a concern that hinders large-scale biofuel production and utilization. Search for novel CAZymes with superior activity and stability under industrial condition has become a major research focus in this area considering the fact that the most conventional CAZymes has low commercial viability. The gut of plant-eating herbivores and other organisms is a potential source of CAZyme with high efficiency. The review explores the potential of the gut microbiome of various organisms in the production of an efficient CAZyme system and the challenges in using the biofuels produced through this approach as an alternative to conventional biofuels.

Characterization of a novel GH10 alkali-thermostable xylanase from a termite microbiome

The aim of the present study was to assess the biochemical and molecular structural characteristics of a novel alkali-thermostable GH10 xylanase (Xyl10B) identified in a termite gut microbiome by a shotgun metagenomic approach. This endoxylanase candidate was amplified, cloned, heterologously expressed in Escherichia coli and purified. The recombinant enzyme was active at a broad range of temperatures (37-60 ºC) and pH values (4-10), with optimal activity at 50 ºC and pH 9. Moreover, its activity remained at more than 80% of its maximum at 50 °C for 8 h. In addition, Xyl10B was found to be stable in the presence of salt and several ions and chemical reagents frequently used in the industry. These characteristics make this enzyme an interesting candidate for pulp and paper bleaching industries, since this process requires enzymes without cellulase activity and resistant to high temperatures and alkaline pH (thermo-alkaliphilic enzymes). The products of xylan hydrolysis by Xyl10B (short xylooligosaccharides, xylose and xylobiose) could be suitable for application as prebiotics and in the production of bioethanol.

Overview of lignocellulolytic enzyme systems with special reference to valorization of lignocellulosic biomass

Lignocellulosic biomass, one of the most valuable natural resources, is abundantly present on earth. Being a renewable feedstock, it harbors a great potential to be exploited as a raw material, to produce various value-added products. Lignocellulolytic microorganisms hold a unique position regarding the valorization of lignocellulosic biomass as they contain efficient enzyme systems capable of degrading this biomass. The ubiquitous nature of these microorganisms and their survival under extreme conditions have enabled their use as an effective producer of lignocellulolytic enzymes with improved biochemical features crucial to industrial bioconversion processes. These enzymes can prove to be an exquisite tool when it comes to the eco-friendly manufacturing of value-added products using waste material. This review focuses on highlighting the significance of lignocellulosic biomass, microbial sources of lignocellulolytic enzymes and their use in the formation of useful products.

Diversity structure of the microbial communities in the guts of four neotropical termite species

The termite gut microbiome is dominated by lignocellulose degrading microorganisms. This study describes the intestinal microbiota of four Argentinian higher termite species with different feeding habits: Microcerotermes strunckii (hardwood), Nasutitermes corniger (softwood), Termes riograndensis (soil organic matter/grass) and Cornitermes cumulans (grass) by deep sequencing of amplified 16S rRNA and ITS genes. In addition, we have performed a taxonomic and gut community structure comparison incorporating into the analysis the previously reported microbiomes of additional termite species with varied diets. The bacterial phylum Spirochaetes was dominant in the guts of M. strunckii, N. corniger and C. cumulans, whereas Firmicutes predominated in the T. riograndensis gut microbiome. A single bacterial genus, Treponema (Spirochaetes), was dominant in all termite species, except for T. riograndensis. Both in our own sequenced samples and in the broader comparison, prokaryotic α-diversity was higher in the soil/grass feeders than in the wood feeders. Meanwhile, the β-diversity of prokaryotes and fungi was highly dissimilar among strict wood-feeders, whereas that of soil- and grass-feeders grouped more closely. Ascomycota and Basidiomycota were the only fungal phyla that could be identified in all gut samples, because of the lack of reference sequences in public databases. In summary, higher microbial diversity was recorded in termites with more versatile feeding sources, providing further evidence that diet, along with other factors (e.g., host taxonomy), influences the microbial community assembly in the termite gut.

Neotropical termite microbiomes as sources of novel plant cell wall degrading enzymes

In this study, we used shotgun metagenomic sequencing to characterise the microbial metabolic potential for lignocellulose transformation in the gut of two colonies of Argentine higher termite species with different feeding habits, Cortaritermes fulviceps and Nasutitermes aquilinus. Our goal was to assess the microbial community compositions and metabolic capacity, and to identify genes involved in lignocellulose degradation. Individuals from both termite species contained the same five dominant bacterial phyla (Spirochaetes, Firmicutes, Proteobacteria, Fibrobacteres and Bacteroidetes) although with different relative abundances. However, detected functional capacity varied, with C. fulviceps (a grass-wood-feeder) gut microbiome samples containing more genes related to amino acid metabolism, whereas N. aquilinus (a wood-feeder) gut microbiome samples were enriched in genes involved in carbohydrate metabolism and cellulose degradation. The C. fulviceps gut microbiome was enriched specifically in genes coding for debranching- and oligosaccharide-degrading enzymes. These findings suggest an association between the primary food source and the predicted categories of the enzymes present in the gut microbiomes of each species. To further investigate the termite microbiomes as sources of biotechnologically relevant glycosyl hydrolases, a putative GH10 endo-β-1,4-xylanase, Xyl10E, was cloned and expressed in Escherichia coli. Functional analysis of the recombinant metagenome-derived enzyme showed high specificity towards beechwood xylan (288.1 IU/mg), with the optimum activity at 50 °C and a pH-activity range from 5 to 10. These characteristics suggest that Xy110E may be a promising candidate for further development in lignocellulose deconstruction applications.

Sugarcane Bagasse as an Efficient Biosorbent for Methylene Blue Removal: Kinetics, Isotherms and Thermodynamics

Adsorption in biomass has proven to be a cost-effective option for treatment of wastewater containing dyes and other pollutants, as it is a simple and low cost technique and does not require high initial investments. The present work aimed to study the adsorption of methylene blue dye (MB) using sugarcane bagasse (SCB). The biomass was characterized by scanning electron microscopy (SEM). Adsorption studies were conducted batchwise. Kinetics, adsorption isotherms, and thermodynamics were studied. The results showed that SCB presented a maximum adsorption capacity of 9.41 mg g^-1 at 45 °C after 24 h of contact time. Adsorption kinetics data better fitted the pseudo-second order model, indicating a chemical process was involved. The Sips's three-parameter isotherm model was better for adjusting the data obtained for the adsorption isotherms, indicating a heterogeneous adsorption process. The process showed to be endothermic, spontaneous, and feasible. Therefore, it was concluded that SCB presented as a potential biosorbent material for the treatment of MB-contaminated waters.

Molecular evidence that cellulolytic bacterial genus Cohnella is widespread among Neotropical Nasutitermitinae from NE Argentina

Cohnella is a highly cellulolytic bacterial genus, which can be found in a variety of habitats. The aim of this study was to assess its presence in the digestive tract of termite species collected in North-eastern Argentina: Nasutitermes aquilinus, N. corniger and Cortaritermes fulviceps. Gut homogenates were incubated with cellulosic substrate for bacterial growth. Bacterial 16S rDNA was partially amplified using new primers for Cohnella spp. and cloned. Sequences obtained showed highest similarity (97.2-99.9%) with those of Cohnella spp. previously reported from diverse environments. Phylogenetic analysis tended to group the clones according to their host species and sampling sites. These results indicate the association of Cohnella-related intestinal symbionts with three common Neotropical termites. Their potential industrial application encourages further research.

Effect of Different Lignocellulosic Diets on Bacterial Microbiota and Hydrolytic Enzyme Activities in the Gut of the Cotton Boll Weevil (Anthonomus grandis)

Cotton boll weevils, Anthonomus grandis, are omnivorous coleopteran that can feed on diets with different compositions, including recalcitrant lignocellulosic materials. We characterized the changes in the prokaryotic community structure and the hydrolytic activities of A. grandis larvae fed on different lignocellulosic diets. A. grandis larvae were fed on three different artificial diets: cottonseed meal (CM), Napier grass (NG) and corn stover (CS). Total DNA was extracted from the gut samples for amplification and sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. Proteobacteria and Firmicutes dominated the gut microbiota followed by Actinobacteria, Spirochaetes and a small number of unclassified phyla in CM and NG microbiomes. In the CS feeding group, members of Spirochaetes were the most prevalent, followed by Proteobacteria and Firmicutes. Bray-Curtis distances showed that the samples from the CS community were clearly separated from those samples of the CM and NG diets. Gut extracts from all three diets exhibited endoglucanase, xylanase, β-glucosidase and pectinase activities. These activities were significantly affected by pH and temperature across different diets. We observed that the larvae reared on a CM showed significantly higher activities than larvae reared on NG and CS. We demonstrated that the intestinal bacterial community structure varies depending on diet composition. Diets with more variable and complex compositions, such as CS, showed higher bacterial diversity and richness than the two other diets. In spite of the detected changes in composition and diversity, we identified a core microbiome shared between the three different lignocellulosic diets. These results suggest that feeding with diets of different lignocellulosic composition could be a viable strategy to discover variants of hemicellulose and cellulose breakdown systems.