Production and characterization of a novel antifungal chitinase identified by functional screening of a suppressive-soil metagenome

Production and characterization of Trichoderma asperellum chitinases and their use in synergy with Bacillus thuringiensis for lepidopteran control

BACKGROUND

Despite their known negative effects on ecosystems and human health, synthetic pesticides are still largely used to control crop insect pests. Currently, the biopesticide market for insect biocontrol mainly relies on the entomopathogenic bacterium Bacillus thuringiensis (Bt). New biocontrol tools for crop protection might derive from fungi, in particular from Trichoderma spp., which are known producers of chitinases and other bioactive compounds able to negatively affect insect survival.

RESULTS

In this study, we first developed an environmentally sustainable production process for obtaining chitinases from Trichoderma asperellum ICC012. Then, we investigated the biological effects of this chitinase preparation - alone or in combination with a Bt-based product - when orally administered to two lepidopteran species. Our results demonstrate that T. asperellum efficiently produces a multi-enzymatic cocktail able to alter the chitin microfibril network of the insect peritrophic matrix, resulting in delayed development and larval death. The co-administration of T. asperellum chitinases and sublethal concentrations of Bt toxins increased larval mortality. This synergistic effect was likely due to the higher amount of Bt toxins that passed the damaged peritrophic matrix and reached the target receptors on the midgut cells of chitinase-treated insects.

CONCLUSION

Our findings may contribute to the development of an integrated pest management technology based on fungal chitinases that increase the efficacy of Bt-based products, mitigating the risk of Bt-resistance development. © 2024 Society of Chemical Industry.

Partitioning recombinant chitinase from Nicotiana benthamiana by an aqueous two-phase system based on polyethylene glycol and phosphate salts

The objectives of this study were to purify 42 kDa chitinase derived from Trichoderma asperellum SH16 produced in Nicotiana benthamiana by a polyethylene glycol (PEG)/salt aqueous two-phase system (ATPS). The specific activities of the crude chitinase and the partially purified chitinase from N. benthamiana were about 251 unit/mg and 386 unit/mg, respectively. The study found the 300 g/L PEG 6000 + 200 g/L potassium phosphate (PP) and 300 g/L PEG 6000 + 150 g/L sodium phosphate (SP) systems had the highest partitioning efficiency for each salt in primary extraction. However, among the two types of salt, PP displayed higher efficiency than SP, with a partitioning coefficient K of 4.85 vs. 3.89, a volume ratio V of 2.94 vs. 2.68, and a partitioning yield Y of approximately 95 % vs. 83 %. After back extraction, the enzymatic activity of purified chitinase was up to 834 unit/mg (PP) and 492 unit/mg (SP). The purification factors reached 3.32 (PP) and 1.96 (SP), with recovery yields of about 59 % and 61 %, respectively. SDS-PAGE and zymogram analysis showed that the recombinant chitinase was significantly purified by using ATPS. The purified enzyme exhibited high chitinolytic activity, with the hydrolysis zone's diameter being around 2.5 cm-3 cm. It also dramatically reduced the growth of Sclerotium rolfsii; the colony diameter after treatment with 60 unit of enzyme for 104 spores was only about 1 cm, compared to 3.5 cm in the control. The antifungal effect of chitinase suggests that this enzyme has great potential for applications in agricultural production as well as postharvest fruit and vegetable preservation.

Transplantation of soil from organic field confers disease suppressive ability to conducive soil

Organic agriculture is a sustainable method of farming, and confers disease-suppressing abilities to disease-conducive soils via specialized soil microbiomes. This study aimed at transforming a disease-conducive soil from a conventional field into disease-suppressive soil by inoculating soil from an organic field previously established as "disease-suppressive". The effectiveness of the transformed soil was established with the model plant wheat (Triticum aestivum) grown under natural conditions, with regard to its potential in inhibiting fungal phytopathogens, Rhizoctonia solani and Fusarium oxysporum. The conducive soil inoculated with the disease-suppressive soil performed better than the control conducive soil in terms of reduced disease severity in plants, improved soil nutrient content, increased activity of hydrolytic enzymes, and increased abundance of structural and functional microbial markers. The study demonstrates the efficacy of the soil microbiome under long-term organic agriculture in transforming disease-conducive soil into disease-suppressive soils. Such practises are simple and easy to implement, and could greatly improve the sustainability and crop yield in developing countries.

Role of Fungi in Imparting General Disease Suppressiveness in Soil from Organic Field

Soil microbial communities are key players responsible for imparting suppressive potential to the soil against soil-borne phytopathogens. Fungi have an immense potential to inhibit soil-borne phytopathogens, but the fungal counterpart has been less explored in this context. We assessed the composition of fungal communities in soil under long-term organic and conventional farming practice, and control soil. The disease-suppressive potential of organic field was already established. A comparative analysis of the disease suppressiveness contributed by the fungal component of soil from conventional and organic farms was assessed using dual culture assays. The quantification of biocontrol markers and total fungi was done; the characterization of fungal community was carried out using ITS-based amplicon sequencing. Soil from organic field exhibited higher disease-suppressive potential than that from conventional farming, against the pathogens selected for the study. Higher levels of hydrolytic enzymes such as chitinase and cellulase, and siderophore production were observed in soil from the organic field compared to the conventional field. Differences in community composition were observed under conventional and organic farming, with soil from organic field exhibiting specific enrichment of key biocontrol fungal genera. The fungal alpha diversity was lower in soil from the organic field compared to the conventional field. Our results highlight the role of fungi in contributing to general disease-suppressive ability of the soil against phytopathogens. The identification of fungal taxa specifically associated with organic farming can aid in understanding the mechanism of disease suppression under such a practice, and can be exploited to induce general disease suppressiveness in otherwise conducive soil.

Multiple enzymatic approaches to hydrolysis of fungal β-glucans by the soil bacterium Chitinophaga pinensis

The genome of the soil Bacteroidota Chitinophaga pinensis encodes a large number of glycoside hydrolases (GHs) with noteworthy features and potentially novel functions. Several are predicted to be active on polysaccharide components of fungal and oomycete cell walls, such as chitin, β-1,3-glucan and β-1,6-glucan. While several fungal β-1,6-glucanase enzymes are known, relatively few bacterial examples have been characterised to date. We have previously demonstrated that C. pinensis shows strong growth using β-1,6-glucan as the sole carbon source, with the efficient release of oligosaccharides from the polymer. We here characterise the capacity of the C. pinensis secretome to hydrolyse the β-1,6-glucan pustulan and describe three distinct enzymes encoded by its genome, all of which show different levels of β-1,6-glucanase activity and which are classified into different GH families. Our data show that C. pinensis has multiple tools to deconstruct pustulan, allowing the species' broad utility of this substrate, with potential implications for bacterial biocontrol of pathogens via cell wall disruption. Oligosaccharides derived from fungal β-1,6-glucans are valuable in biomedical research and drug synthesis, and these enzymes could be useful tools for releasing such molecules from microbial biomass, an underexploited source of complex carbohydrates.

Functional Metagenomics as a Tool to Tap into Natural Diversity of Valuable Biotechnological Compounds

The marine ecosystem covers more than 70% of the world's surface, and oceans represent a source of varied types of organisms due to the diversified environment. Consequently, the marine environment is an exceptional depot of novel bioactive natural products, with structural and chemical features generally not found in terrestrial habitats. Here, in particular, microbes represent a vast source of unknown and probably new physiological characteristics. They have evolved during extended evolutionary processes of physiological adaptations under various environmental conditions and selection pressures. However, to date, the biodiversity of marine microbes and the versatility of their bioactive compounds and metabolites have not been fully explored. Thus, metagenomic tools are required to exploit the untapped marine microbial diversity and their bioactive compounds. This chapter focuses on function-based marine metagenomics to screen for bioactive molecules of value for biotechnology. Functional metagenomic strategies are described, including sampling in the marine environment, constructing marine metagenomic large-insert libraries, and examples on function-based screens for quorum quenching and anti-biofilm activities.

Discovery of novel carbohydrate degrading enzymes from soda lakes through functional metagenomics

Extremophiles provide a one-of-a-kind source of enzymes with properties that allow them to endure the rigorous industrial conversion of lignocellulose biomass into fermentable sugars. However, the fact that most of these organisms fail to grow under typical culture conditions limits the accessibility to these enzymes. In this study, we employed a functional metagenomics approach to identify carbohydrate-degrading enzymes from Ethiopian soda lakes, which are extreme environments harboring a high microbial diversity. Out of 21,000 clones screened for the five carbohydrate hydrolyzing enzymes, 408 clones were found positive. Cellulase and amylase, gave high hit ratio of 1:75 and 1:280, respectively. A total of 378 genes involved in the degradation of complex carbohydrates were identified by combining high-throughput sequencing of 22 selected clones and bioinformatics analysis using a customized workflow. Around 41% of the annotated genes belonged to the Glycoside Hydrolases (GH). Multiple GHs were identified, indicating the potential to discover novel CAZymes useful for the enzymatic degradation of lignocellulose biomass from the Ethiopian soda Lakes. More than 73% of the annotated GH genes were linked to bacterial origins, with Halomonas as the most likely source. Biochemical characterization of the three enzymes from the selected clones (amylase, cellulase, and pectinase) showed that they are active in elevated temperatures, high pH, and high salt concentrations. These properties strongly indicate that the evaluated enzymes have the potential to be used for applications in various industrial processes, particularly in biorefinery for lignocellulose biomass conversion.

Biological Characteristics of Recombinant Arthrobotrys oligospora Chitinase AO-801

Chitinase AO-801 is a hydrolase secreted by Arthrobotrys oligospora during nematode feeding, while its role remained elusive. This study analyzed the molecular characteristics of recombinant chitinase of Arthrobotrys oligospora (reAO-801). AO-801 belongs to the typical glycoside hydrolase 18 family with conserved chitinase sequence and tertiary structure of (α/β)8 triose-phosphate isomerase (TIM) barrel. The molecular weight of reAO-801 was 42 kDa. reAO-801 effectively degraded colloidal and powdered chitin, egg lysate, and stage I larval lysate of Caenorhabditis elegans. The activity of reAO-801 reached its peak at 40˚C and pH values between 4-7. Enzyme activity was inhibited by Zn2+, Ca2+, and Fe3+, whereas Mg2+ and K+ potentiated its activity. In addition, urea, sodium dodecyl sulfate, and 2-mercaptoethanol significantly inhibited enzyme activity. reAO-801 showed complete nematicidal activity against C. elegans stage I larvae. reAO-801 broke down the C. elegans egg shells, causing them to die or die prematurely by hatching the eggs. It also invoked degradation of Haemonchus contortus eggs, resulting in apparent changes in the morphological structure. This study demonstrated the cytotoxic effect of reAO-801, which laid the foundation for further dissecting the mechanism of nematode infestation by A. oligospora.

Solubilization and Refolding of Inclusion Body Proteins

Expression of heterologous proteins in E. coli often leads to the formation of protein aggregates known as inclusion bodies (IBs). Inclusion body aggregates pose a major hurdle in the recovery of bioactive proteins from E. coli. Usage of strong denaturing buffers for solubilization of bacterial IBs results in poor recovery of bioactive protein. Structure-function understanding of IBs in the last two decades have led to the development of several mild solubilization buffers, which improve the recovery of bioactive from IBs. Recently, combinatorial mild solubilization methods have paved the way for solubilization of wide range of inclusion bodies with appreciable refolding yield. Here, we describe a simple protocol for solubilization and refolding of an inclusion body protein with appreciable recovery.

Identification and Characterization of a Novel Plasmid-Encoded Laccase-Like Multicopper Oxidase from Ochrobactrum sp. BF15 Isolated from an On-Farm Bio-Purification System

RESEARCH BACKGROUND

In recent decades, laccases (p-diphenol-dioxygen oxidoreductases; EC 1.10.3.2) have attracted the attention of researchers due to their wide range of biotechnological and industrial applications. Laccases can oxidize a variety of organic and inorganic compounds, making them suitable as biocatalysts in biotechnological processes. Even though the most traditionally used laccases in the industry are of fungal origin, bacterial laccases have shown an enormous potential given their ability to act on several substrates and in multiple conditions. The present study aims to characterize a plasmid-encoded laccase-like multicopper oxidase (LMCO) from Ochrobactrum sp. BF15, a bacterial strain previously isolated from polluted soil.

EXPERIMENTAL APPROACH

We used in silico profile hidden Markov models to identify novel laccase-like genes in Ochrobactrum sp. BF15. For laccase characterization, we performed heterologous expression in Escherichia coli, purification and activity measurement on typical laccase substrates.

RESULTS AND CONCLUSIONS

Profile hidden Markov models allowed us to identify a novel LMCO, named Lac80. In silico analysis of Lac80 revealed the presence of three conserved copper oxidase domains characteristic of three-domain laccases. We successfully expressed Lac80 heterologously in E. coli, allowing us to purify the protein for further activity evaluation. Of thirteen typical laccase substrates tested, Lac80 showed lower activity on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), pyrocatechol, pyrogallol and vanillic acid, and higher activity on 2,6-dimethoxyphenol.

NOVELTY AND SCIENTIFIC CONTRIBUTION

Our results show Lac80 as a promising laccase for use in industrial applications. The present work shows the relevance of bacterial laccases and highlights the importance of environmental plasmids as valuable sources of new genes encoding enzymes with potential use in biotechnological processes.

The discovery and characterization of a novel chitinase with dual catalytic domains from a Qinghai-Tibetan Plateau wetland soil metagenome

A novel chitinase (P1724) was discovered from a Qinghai-Tibetan plateau microbial metagenome. P1724 contains two GH18 family catalytic domains and is phylogenetically distant from any of the chitinases studied. P1724 and its truncated versions, P1724(∆cGH18) and P1724(∆nGH18), were produced in Escherichia coli and characterized. Using colloidal chitin as substrate, the three recombinant proteins showed maximum hydrolytic activities at 40 °C, pH 5.0-6.0 and 0-0.5 M NaCl, and were cold adaptive, as they remained active at 4 °C; their chitinase activities were decreased with the presence of Cu²⁺ and EDTA, but increased with Ba²⁺ and Ca²⁺; they all showed both chitobiosidase and endochitinase activities. Compared to P1724(∆nGH18), P1724 and P1724(∆cGH18) shared more similarities in temperature and pH stabilities, NaCl tolerance, and substrate affinity, suggesting the N-terminal GH18 domain contributed more than the C-terminal GH18 did in biochemical characteristics of P1724. k_cat/K_m value of P1724 was significantly higher than the sum values of P1724(∆cGH18) and P1724(∆nGH18), which indicated that two GH18 domains of P1724 worked cooperatively in degrading chitin. This study has not only broadened the understanding of unknown chitinases in nature but also discussed the strategy of adding additional catalytic domains in enzyme engineering.

Biochemical characterization of a novel acidic chitinase with antifungal activity from Paenibacillus xylanexedens Z2-4

A chitinase gene (PxChi52) from Paenibacillus xylanexedens Z2-4 was cloned and heterologously expressed in Escherichia coli BL21 (DE3). PxChi52 shared the highest identity of 91% with a glycoside hydrolase family 18 chitinase (ChiD) from Bacillus circulans. The recombinant enzyme (PxChi52) was purified and biochemically characterized. PxChi52 had a molecular mass of 52.8 kDa. It was most active at pH 4.5 and 65 °C, respectively, and stable in a wide pH range of 4.0-13.0 and up to 50 °C. The enzyme exhibited the highest specific activity of 16.0 U/mg towards colloidal chitin, followed by ethylene glycol chitin (5.4 U/mg) and ball milled chitin (0.4 U/mg). The K_m and V_max values of PxChi52 towards colloidal chitin were determined to be 3.06 mg/mL and 71.38 U/mg, respectively, PxChi52 hydrolyzed colloidal chitin and chitooligosaccharides with degree of polymerization 2-5 to release mainly N-acetyl chitobiose. In addition, PxChi52 displayed inhibition effects on the growth of some phytopathogenic fungi, including Alternaria alstroemeriae, Botrytis cinerea, Rhizoctonia solani, Sclerotinia sclerotiorum and Valsa mali. The unique properties of PxChi52 may enable it potential application in agriculture field as a biocontrol agent.

Genomics as a potential tool to unravel the rhizosphere microbiome interactions on plant health

Intense agricultural practices to meet rising food demands have caused ecosystem perturbations. For sustainable crop production, biological agents are gaining attention, but exploring their functional potential on a multi-layered complex ecosystem like the rhizosphere is challenging. This review explains the significance of genomics as a culture-independent molecular tool to understand the diversity and functional significance of the rhizosphere microbiome for sustainable agriculture. It discusses the recent significant studies in the rhizosphere environment carried out using evolving techniques like metagenomics, metatranscriptomics, and metaproteomics, their challenges, constraints infield application, and prospective solutions. The recent advances in techniques such as nanotechnology for the development of bioformulations and visualization techniques contemplating environmental safety were also discussed. The need for development of metagenomic data sets of regionally important crops, their plant microbial interactions and agricultural practices for narrowing down significant data from huge databases have been suggested. The role of taxonomical and functional diversity of soil microbiota in understanding soil suppression and part played by the microbial metabolites in the process have been analyzed and discussed in the context of 'omics' approach. 'Omics' studies have revealed important information about microbial diversity, their responses to various biotic and abiotic stimuli, and the physiology of disease suppression. This can be translated to crop sustainability and combinational approaches with advancing visualization and analysis methodologies fix the existing knowledge gap to a huge extend. With improved data processing and standardization of the methods, details of plant-microbe interactions can be successfully decoded to develop sustainable agricultural practices.

Recent advances in the bioprospection and applications of chitinolytic bacteria for valorization of waste chitin

One of the most abundant natural polymers on earth, chitin is a fibrous and structural polysaccharide, composed of N-acetyl-D-glucosamine. The biopolymer is the major structural constituent of fungi, arthropods, mollusks, nematodes, and some algae. The biodegradation of chitin is largely manifested by chitinolytic enzyme secreting organisms including bacteria, insects, and plants. Among them, bacterial chitinases represent the most promising, inexpensive, and sustainable source of proteins that can be employed for industrial-scale applications. To this end, the presented review comes at a timely moment to highlight the major sources of chitinolytic bacteria. It also discusses the potential pros and cons of prospecting bacterial chitinases that can be easily manipulated through genetic engineering. Additionally, we have elaborated the recent applications of the chitin thereby branding chitinases as potential candidates for biorefinery and biomedical research for eco-friendly and sustainable management of chitin waste in the environment.

Enzymatic production of sugar from fungi and fungi-infected lignocellulosic biomass by a new cellulosomal enzyme harboring N-acetyl-β-d-glucosaminidase activity

Cellulosomes are scaffold proteins displaying enzymes on the cell wall to efficiently obtain nutrient sources. CcGlcNAcase is a novel cellulosomal component. Based on sequence analysis, CcGlcNAcase was predicted to be a chitinolytic enzyme based on high homology with the discoidin domain-containing protein and chitobiase/ β-hexosaminidase C terminal domain. CcGlcNAcase expression was notably increased when chitin was present. CcGlcNAcase produced N-acetyl-d-glucosamine from various lengths of N-acetyl-d-glucosamine. CcGlcNAcase bound to chitin (89%) and fungi (54.10%), whereas CcGlcNAcase exhibited a low binding ability to cellulose and xylan. CcGlcNAcase hydrolyzed fungi, yielding maximum 3.90 g/L N-acetyl-d-glucosamine. CcGlcNAcase enhanced cellulase toward fungi-infected lignocellulosic biomass, yielding 18 mg/L glucose (1.32-fold) and 1.72-fold increased total reducing sugar levels, whereas cellulase alone produced 13 mg/L glucose. Taken together, CcGlcNAcase can be utilized to enhance the degradation of fungi-infected lignocellulosic biomass and exhibits potential applications in the wood and sugar industry.

Protection of surplus food from fungal spoilage using Streptomyces spp.: a green approach

Consortia of Streptomyces spp. (colonies 169, 194, 165 and 130) used in this study are an efficient producer of secondary metabolites like chitinases and antifungal compounds, which may help in the protection of surplus food from spoilage. Qualitative screening for chitinase production and taxonomy of these colonies were undertaken in our previous studies. In the current study, GC-MS analysis of extract produced from the consortia of Streptomyces strains was done for the identification of antifungal compounds. Treatment of surplus food with activated consortia of Streptomyces spp. has protected powdered food for a month, whereas fresh food (unpowdered) was preserved for two days. A control sample of surplus food (untreated) was kept to check the contamination, which resulted in the growth of three fungi (FP-1, FG-1, and FB-1). Taxonomic characterization of fungi and identification of toxic compounds produced from them were done by ITS amplification and GC-MS analysis, respectively. The study shows that the secondary metabolites from Streptomyces spp. have the potential to protect the food from mycotoxin contamination. Based on literature reports, this is for the first time that bioactive compounds and chitinases produced from Streptomyces are being used for the protection and management of surplus food.

A potent chitin-hydrolyzing enzyme from Myrothecium verrucaria affects growth and development of Helicoverpa armigera and plant fungal pathogens

Chitin, a crucial structural and functional component of insects and fungi, serves as a target for pest management by utilizing novel chitinases. Here, we report the biocontrol potential of recombinant Myrothecium verrucaria endochitinase (rMvEChi) against insect pest and fungal pathogens. A complete ORF of MvEChi (1185 bp) was cloned and heterologously expressed in Escherichia coli. Structure based sequence alignment of MvEChi revealed the presence of conserved domains SXGG and DXXDXDXE specific for GH-18 family, involved in substrate binding and catalysis, respectively. rMvEChi (46.6 kDa) showed optimum pH and temperature as 7.0 and 30 °C, respectively. Furthermore, rMvEChi remained stable within the pH range of 6.0 to 8.0 and up to 40 °C. rMvEChi exhibited k_cat/K_m values of 129.83 × 10³ [(g/L)^-1 s^-1] towards 4MU chitotrioside. Hydrolysis of chitooligosaccharides with various degrees of polymerization (DP) using rMvEChi indicated the release of DP2 as main end product with order of reaction as DP6 > DP5 > DP4 > DP3. Bioassay of rMvEChi against Helicoverpa armigera displayed potent anti-feedant activity and induced mortality. In vitro antifungal activity against plant pathogenic fungi (Ustilago maydis and Bipolaris sorokiniana) exhibited significant inhibition of mycelium growth. These results suggest that MvEChi has significant potential in enzyme-based pest and pathogen management.

Metagenome-Sourced Microbial Chitinases as Potential Insecticide Proteins

Microbial chitinases are gaining interest as promising candidates for controlling plant pests. These enzymes can be used directly as biocontrol agents as well as in combination with chemical pesticides or other biopesticides, reducing their environmental impact and/or enhancing their efficacy. Chitinolytic enzymes can target two different structures in insects: the cuticle and the peritrophic matrix (PM). PM, formed by chitin fibrils connected to glycoproteins and proteoglycans, represents a physical barrier that plays an essential role in midgut physiology and insect digestion, and protects the absorptive midgut epithelium from food abrasion or pathogen infections. In this paper, we investigate how two recently discovered metagenome-sourced chitinases (Chi18H8 and 53D1) affect, in vitro and in vivo, the PM integrity of Bombyx mori, a model system among Lepidoptera. The two chitinases were produced in Escherichia coli or, alternatively, in the unconventional – but more environmentally acceptable – Streptomyces coelicolor. Although both the proteins dramatically altered the structure of B. mori PM in vitro, when administered orally only 53D1 caused adverse and marked effects on larval growth and development, inducing mortality and reducing pupal weight. These in vivo results demonstrate that 53D1 is a promising candidate as insecticide protein.

Production and characterization of a thermostable antifungal chitinase secreted by the filamentous fungus Aspergillus niveus under submerged fermentation

The filamentous fungus Aspergillus niveus produced extracellular antifungal chitinase when cultured under submerged fermentation (SbmF) using crab shells as the carbon source. Maximal chitinase production was achieved at 192 h of cultivation using minimal medium containing 1% chitin. The enzyme was purified 1.97-fold with 40% recovery by ammonium sulfate precipitation and Sephadex G-100 gel filtration. The molecular mass was estimated to be 44 kDa by both 12% SDS-PAGE and Sepharose CL-6B gel filtration. Maximal A. niveus chitinase activity was obtained at 65 °C and pH 5.0. The enzyme was fully stable at 60 °C for up to 120 min and the enzymatic activity was increased by Mn²⁺. In the presence of reducing and denaturing compounds, the enzyme activity was not drastically affected. The chitinase was able to hydrolyze colloidal chitin, azure chitin, and 4-nitrophenyl N-acetyl-β-D glucosaminide; for the latter, the K_0.5 and maximal velocity (V_max) were 3.51 mM and 9.68 U/mg of protein, respectively. The A. niveus chitinase presented antifungal activity against Aspergillus niger (MIC = 84 µg/mL), A. fumigatus (MIC = 21 µg/mL), A. flavus (MIC = 24 µg/mL), A. phoenicis (MIC = 24 µg/mL), and Paecilomyces variotii (MIC = 21 µg/mL). The fungus A. niveus was able to produce a thermostable and denaturation-resistant chitinase able to inhibit fungal development, signaling its biotechnological potential.

Improving the thermostability of Serratia marcescens B4A chitinase via G191V site-directed mutagenesis

Chitinases with high thermostability are important for many industrial and biotechnological applications. This study was conducted to enhance the stability of Serratia marcescens B4A chitinase by site directed mutagenesis of G191 V. Further characterization showed that the thermal stability of the mutant showed marked increase of about 5 and 15 fold at 50 and 60 °C respectively, while the optimum temperature and pH was retained. Kinetic analysis showed decreased K_m and V_max of the mutant in comparison with the wild type chitinase of about 1.3 and 3 fold, respectively. Based on structural prediction, it was speculated that this replacement shortened an important loop concomitant with the extension of adjacent β sheets. Accordingly, a higher thermostability of G191 V up to 90 °C supporting the decreased flexibility of unfolded state was also indicated. Finally, a practical proof of kinetic and thermal stabilization of chitinase was provided through decreased flexibility and entropic stabilization of its surface loops.

Identification and characterization of a novel alkalistable and salt-tolerant esterase from the deep-sea hydrothermal vent of the East Pacific Rise

A novel esterase gene selected from metagenomic sequences of deep-sea hydrothermal vents was successfully expressed in Escherichia coli. The recombinant protein (est-OKK), which belongs to the lipolytic enzyme family V, exhibited high activity toward pNP-esters with short acyl chains and especially p-nitrophenyl butyrate. Site-mutagenesis results confirmed that est-OKK contains the nonclassical catalytic tetrad predicted by alignment and computational modeling. The est-OKK protein is a moderately thermophilic enzyme that is relatively thermostable, and highly salt-tolerant, which remained stable in 3 mol/L NaCl for 6 hr. The est-OKK protein showed the considerable alkalistability, displayed optimal activity at pH 9.0 and maintained approximately 70% of its residual activity after incubation at pH 10 for 4 hr. Furthermore, the est-OKK activity was strongly resistant to a variety of metal ions such as Co²⁺ , Zn²⁺ , Fe²⁺ , Na⁺ , and K⁺ ; nonionic detergents such as Tween-20, Tween-80; and organic solvents such as acetone and isopropanol. Taken together, the novel esterase with unique characteristics may give us a new insight into the family V of lipolytic enzymes, and could be a highly valuable candidate for biotechnological applications such as organic synthesis reactions or food and pharmaceutical industries.

Antimicrobial and Anti-Proliferative Effects of Skin Mucus Derived from Dasyatis pastinaca (Linnaeus, 1758)

Resistance to chemotherapy occurs in various diseases (i.e., cancer and infection), and for this reason, both are very difficult to treat. Therefore, novel antimicrobial and chemotherapic drugs are needed for effective antibiotic therapy. The aim of the present study was to assess the antimicrobial and anti-proliferative effects of skin mucus derived from Dasyatis pastinaca (Linnaeus, 1758). Our results showed that skin mucus exhibited a significant and specific antibacterial activity against Gram-negative bacteria but not against Gram-positive bacteria. Furthermore, we also observed a significant antifungal activity against some strains of Candida spp. Concerning anti-proliferative activity, we showed that fish mucus was specifically toxic for acute leukemia cells (HL60) with an inhibition of proliferation in a dose dependent manner (about 52% at 1000 μg/mL of fish skin mucous, FSM). Moreover, we did not observe effects in healthy cells, in neuroblastoma cells (SH-SY5Y), and multiple myeloma cell lines (MM1, U266). Finally, it exhibited strong expression and activity of chitinase which may be responsible, at least in part, for the aforementioned results.