Production of a Thermostable and Alkaline Chitinase by Bacillus thuringiensis subsp. kurstaki Strain HBK-51

Purification and characterization of Stenotrophomonas maltophilia chitinase with antifungal and insecticidal properties

This study aimed to determine the ability of bacteria to produce the chitinase enzyme, purify, and characterize the enzyme from the isolate with the best activity, and determine the use of this purified enzyme as a biocontrol agent. The chitinolytic bacterium was identified as Stenotrophomonas maltophilia. The chitinase enzyme was purified 1.4 times at a 30% ammonium sulfate concentration with a yield of 40.7%. Following partial purification, the enzyme was purified by ion-exchange chromatography using HiPrep Q XL 16/10 column and HiPrep™ 26/10 desalting column with 25.34% and 18.12% yields, respectively. It was calculated that the purified enzyme had a molecular weight of 52 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The optimum activity of the enzyme was determined at 50 °C and pH 7.0. Enzyme activity was most induced by Fe²⁺, while it was most inhibited by Zn²⁺ at 5 mM concentration. K_m and V_max values of the enzyme for colloidal chitin were calculated as 1.6419 mg/mL and 16.129 U/mg, respectively. The purified chitinase was used as a biocontrol agent against the fungus Fusarium oxysporum and potato beetle Leptinotarsa decemlineata. The enzyme was shown to be effective in reducing the growth of fungus and causing disruption of the chitin structure of potato beetle.

A novel thermophilic chitinase directly mined from the marine metagenome using the deep learning tool Preoptem

Chitin is abundant in nature and its degradation products are highly valuable for numerous applications. Thermophilic chitinases are increasingly appreciated for their capacity to biodegrade chitin at high temperatures and prolonged enzyme stability. Here, using deep learning approaches, we developed a prediction tool, Preoptem, to screen thermophilic proteins. A novel thermophilic chitinase, Chi304, was mined directly from the marine metagenome. Chi304 showed maximum activity at 85 ℃, its Tm reached 89.65 ± 0.22℃, and exhibited excellent thermal stability at 80 and 90 °C. Chi304 had both endo- and exo-chitinase activities, and the (GlcNAc)2 was the main hydrolysis product of chitin-related substrates. The product yields of colloidal chitin degradation reached 97% within 80 min, and 20% over 4 days of reaction with crude chitin powder. This study thus provides a method to mine the novel thermophilic chitinase for efficient chitin biodegradation.

A Contemporary Appraisal on Impending Industrial and Agricultural Applications of Thermophilic-Recombinant Chitinolytic Enzymes from Microbial Sources

The ability of chitinases to degrade the second most abundant polymer, chitin, into potentially useful chitooligomers and chitin derivatives has not only rendered them fit for chitinous waste management but has also made them important from industrial point of view. At the same time, they have also been recognized to have an imperative role as promising biocontrol agents for controlling plant diseases. As thermostability is an important property for an industrially important enzyme, various bacterial and fungal sources are being exploited to obtain such stable enzymes. These stable enzymes can also play a role in agriculture by maintaining their stability under adverse environmental conditions for longer time duration when used as biocontrol agent. Biotechnology has also played its role in the development of recombinant chitinases with enhanced activity, thermostability, fungicidal and insecticidal activity via recombinant DNA techniques. Furthermore, a relatively new approach of generating pathogen-resistant transgenic plants has opened new ways for sustainable agriculture by minimizing the yield loss of valuable crops and plants. This review focuses on the potential applications of thermostable and recombinant microbial chitinases in industry and agriculture.

Glycoside Hydrolases and Glycosyltransferases from Hyperthermophilic Archaea: Insights on Their Characteristics and Applications in Biotechnology

Hyperthermophilic Archaea colonizing unnatural habitats of extremes conditions such as volcanoes and deep-sea hydrothermal vents represent an unmeasurable bioresource for enzymes used in various industrial applications. Their enzymes show distinct structural and functional properties and are resistant to extreme conditions of temperature and pressure where their mesophilic homologs fail. In this review, we will outline carbohydrate-active enzymes (CAZymes) from hyperthermophilic Archaea with specific focus on the two largest families, glycoside hydrolases (GHs) and glycosyltransferases (GTs). We will present the latest advances on these enzymes particularly in the light of novel accumulating data from genomics and metagenomics sequencing technologies. We will discuss the contribution of these enzymes from hyperthermophilic Archaea to industrial applications and put the emphasis on newly identifed enzymes. We will highlight their common biochemical and distinct features. Finally, we will overview the areas that remain to be explored to identify novel promising hyperthermozymes.

Recombinant production and characterisation of two chitinases from Rasamsonia emersonii, and assessment of their potential industrial applicability

Rasamsonia emersonii (previously Talaromyces emersonii) is a thermophilic filamentous fungus displaying optimum growth at 45 °C. It has a history of use in commercial food enzyme production. Its unfractionated chitinolytic secretome was partially characterised in the early 1990s; however, no individual chitinase from this source has been described in literature previously. This study describes two GH18 chitinases originating from the R. emersonii genome, expressed in the methylotrophic yeast P. pastoris. Chit1 comprises of a GH18 catalytic domain and Chit2 comprises of a GH18 catalytic domain and a chitin-binding motif at the C-terminal. The chitinases were expressed as glycoproteins. The apparent molecular weight of Chit1 was 35.8-42.1 kDa with a smearing tail associated with glyco-sidechains visible up to 72.2 kDa. This became two bands of 30.8 and 29.0 kDa upon de-glycosylation. The apparent molecular weight of Chit2 was 50.4 kDa, reducing to 48.2 kDa upon de-glycosylation. Both chitinases displayed endo-chitinase and chitobiosidase activity, temperature optima of 50-55 °C and low pH optima (pH 4.5 or lower); Chit1 displayed a pH optimum of 3.5, retaining > 60% maximum activity at pH 2.2, a pH range lower than most enzymes of fungal origin. Chit2 displayed the highest chitin-degrading ability at 3456 µmol/mg on 4-NP-triacetylchitotriose, but lost activity faster than Chit1, which displayed 403 µmol/mg on the same substrate. The predicted D values (time required to reduce the enzyme activity to 10% of its original value at 50 °C) were 19.2 and 2.3 days for Chit1 and Chit2, respectively. Thus, Chit1 can be considered one of few hyperthermostable chitinase enzymes described in literature to date. Their physicochemical properties render these chitinases likely suitable for shrimp chitin processing including one-step chitin hydrolysis and alternative sustainable protein processing and the attractive emerging application of mushroom food waste valorisation.Key points• Two GH18 chitinases originating from the industrially relevant thermophilic fungus R. emersonii were cloned and expressed in P. pastoris.• The purified recombinant chitinases showed low pH and high temperature optima and appreciable thermostability at industrially relevant temperatures.• The chitinases displayed characteristics that indicate their likely suitability to several industrial applications including sustainable alternative protein processing, food waste valorisation of commercial mushroom production and one-step shrimp chitin processing.

Extracellular Antifungal Activity of Chitinase-Producing Bacteria Isolated From Guano of Insectivorous Bats

A reduction in the use of agrochemicals requires the development of either alternatives or complementary control methods in order to limit their dangerousness. An alternative is the biological control of fungi by bacteria. The fungal cell wall is a unique structure of the fungi, composed of glucan, chitin, and glycoproteins. Therefore, bacteria producing mycolytic enzymes, like chitinases, are of great interest to degrade fungal cell-wall components. The objectives of this work were to isolate chitinolytic bacteria from the guano of insectivorous bats (Tadarida brasiliensis) and to verify the presence of antifungal activities against phytopathogenic fungi. From the guano samples, 28 bacterial isolates were obtained, 70% of which presented chitinolytic activity. Four isolates were selected since they showed the highest values of chitinase activity, and they were characterized as belonging to Bacillus genus, by analyzing the 16S ribosomal RNA gene sequence. Cell-free supernatants of bacterial cultures were used in inhibition tests on 16 fungi: Alternaria and Colletotrichum acutatum were the most affected. Chitinase and antifungal activities were observed in the cell-free supernatant regardless of the culture medium used. Both activities were stable to heat and proteinase K treatments. Finally, when the culture medium was supplemented with 1 ml of cell-free supernatants (0.33%) and incubated for 120 h, the inhibition of hyphae formation and germination spores of reporter fungus were observed under light microscopy. These results suggest the feasibility of using cell-free supernatants as eco-friendly fungicides. The use of them may contribute to reducing the dose of toxic chemicals.

Biotechnological Eminence of Chitinases: A Focus on Thermophilic Enzyme Sources, Production Strategies and Prominent Applications

BACKGROUND

Chitin, the second most abundant polysaccharide in nature, is a constantly valuable and renewable raw material after cellulose. Due to advancement in technology, industrial interest has grown to take advantage of the chitin.

OBJECTIVE

Now, biomass is being treated with diverse microbial enzymes or cells for the production of desired products under best industrial conditions. Glycosidic bonds in chitin structure are degraded by chitinase enzymes, which are characterized into number of glycoside hydrolase (GHs) families.

METHODS

Thermophilic microorganisms are remarkable sources of industrially important thermostable enzymes, having ability to survive harsh industrial processing conditions. Thermostable chitinases have an edge over mesophilic chitinases as they can hydrolyse the substrate at relatively high temperatures and exhibit decreased viscosity, significantly reduced contamination risk, thermal and chemical stability and increased solubility. Various methods are employed to purify the enzyme and increase its yield by optimizing various parameters such as temperature, pH, agitation, and by investigating the effect of different chemicals and metal ions etc. Results: Thermostable chitinase enzymes show high specific activity at elevated temperature which distinguish them from mesophiles. Genetic engineering can be used for further improvement of natural chitinases, and unlimited potential for the production of thermophilic chitinases has been highlighted due to advancement in synthetic biological techniques. Thermostable chitinases are then used in different fields such as bioremediation, medicine, agriculture and pharmaceuticals.

CONCLUSION

This review will provide information about chitinases, biotechnological potential of thermostable enzyme and the methods by which they are being produced and optimized for several industrial applications. Some of the applications of thermostable chitinases have also been briefly described.

2,4-Di-Tert-Butylphenol Isolated From an Endophytic Fungus, Daldinia eschscholtzii, Reduces Virulence and Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa is among the top three gram-negative bacteria according to the WHO’s critical priority list of pathogens against which newer antibiotics are urgently needed and considered a global threat due to multiple drug resistance. This situation demands unconventional antimicrobial strategies such as the inhibition of quorum sensing to alleviate the manifestation of classical resistance mechanisms. Here, we report that 2,4-di-tert-butylphenol (2,4-DBP), isolated from an endophytic fungus, Daldinia eschscholtzii, inhibits the quorum-sensing properties of P. aeruginosa. We have found that treating P. aeruginosa with 2,4-DBP substantially reduced the secretion of virulence factors as well as biofilm, and its associated factors that are controlled by quorum sensing, in a dose-dependent manner. Concomitantly, 2,4-DBP also significantly reduced the expression of quorum sensing-related genes, i.e., lasI, lasR, rhlI, and rhlR significantly. Importantly, 2,4-DBP restricted the adhesion and invasion of P. aeruginosa to the A549 lung alveolar carcinoma cells. In addition, bactericidal assay with 2,4-DBP exhibited synergism with ampicillin to kill P. aeruginosa. Furthermore, our computational studies predicted that 2,4-DBP could bind to the P. aeruginosa quorum-sensing receptors LasR and RhlR. Collectively, these data suggest that 2,4-DBP can be exploited as a standalone drug or in combination with antibiotic(s) as an anti-virulence and anti-biofilm agent to combat the multidrug resistant P. aeruginosa infection.

Biochemical and molecular characterization of an acido-thermostable endo-chitinase from Bacillus altitudinis KA15 for industrial degradation of chitinous waste

This paper reports the isolation and identification of an acido-thermostable chitinase (ChiA-Ba43) which was purified, from the culture liquid of Bacillus altitudinis strain KA15, and characterized. Purification of ChiA-Ba43 produced a 69.6-fold increase in the specific activity (120,000 U/mg) of the chitinase, with a yield of 51% using colloidal chitin as substrate. ChiA-Ba43 was found to be a monomeric protein with a molecular mass of 43,190.05 Da as determined by MALDI-TOF/MS. N-terminal sequence of the first 27 amino-acids (aa) of ChiA-Ba43 displayed homology to chitinases from other Bacillus species. Interestingly, ChiA-Ba43 exhibited optimum pH and temperature of 4-5.5 and 85 °C, respectively. Thin-layer chromatography (TLC) showed that the final hydrolyzed products of the enzyme from chitin-oligosaccharides and colloidal chitin are a mixture of (GlcNAc)₂, (GlcNAc)₃, (GlcNAc)₄, and (GlcNAc)₅, which indicates that ChiA-Ba43 possesses an endo-acting function. More interestingly, compared to ChiA-Mt45, ChiA-Hh59, Chitodextrinase®, N-acetyl-β-glucosaminidase®, and ChiA-65, ChiA-Ba43 demonstrated a high level of catalytic efficiency and outstanding tolerance towards various organic solvents. The chiA-Ba43 gene (1332 bp) encoding ChiA-Ba43 (409 aa) was cloned, sequenced, and expressed in Escherichia coli strain HB101. The biochemical properties of the recombinant chitinase (rChiA-Ba43) were equivalent to those of the natively expressed enzyme. These properties make ChiA-Ba43 an ideal candidate for industrial bioconversion of chitinous waste.

Nocardia farcinica as a cause of chronic meningitis - case report

Background

Nocardiosis is an uncommon disease caused by aerobic gram-positive bacteria Nocardia spp. Although it is usually an opportunistic infection affecting immunocompromised patients, even one third of cases occur in immunocompetent persons. The aim of the study was to describe the course of chronic meningitis due to Nocardia infection.

Case presentation

A 52-year-old patient, chalk miner, suffered from a chronic meningitis caused by an extremely rare pathogen. The patient’s history was complicated and diagnostic process covered multiple examinations and consultations. Initially Kocuria rosea was cultured, yet after molecular examination the result was verified to Nocardia farcinica. Targeted antibiotic treatment was implemented, which resulted in gradual improvement of patients condition. A full recovery was achieved after one year antibiotic therapy.

Conclusions

Nocardia farcinica is an uncommon but possible cause of chronic meningitis.

In the case of a chronic meningitis of unknown origin multiple cerebrospinal fluid cultures should be performed as the identification of pathogen may be crucial for patient’s recovery.

In case of unusual culture, such as Kocuria spp. PCR should be performed.

2,4-Di-Tert-Butylphenol Isolated From an Endophytic Fungus, Daldinia eschscholtzii, Reduces Virulence and Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa is among the top three gram-negative bacteria according to the WHO's critical priority list of pathogens against which newer antibiotics are urgently needed and considered a global threat due to multiple drug resistance. This situation demands unconventional antimicrobial strategies such as the inhibition of quorum sensing to alleviate the manifestation of classical resistance mechanisms. Here, we report that 2,4-di-tert-butylphenol (2,4-DBP), isolated from an endophytic fungus, Daldinia eschscholtzii, inhibits the quorum-sensing properties of P. aeruginosa. We have found that treating P. aeruginosa with 2,4-DBP substantially reduced the secretion of virulence factors as well as biofilm, and its associated factors that are controlled by quorum sensing, in a dose-dependent manner. Concomitantly, 2,4-DBP also significantly reduced the expression of quorum sensing-related genes, i.e., lasI, lasR, rhlI, and rhlR significantly. Importantly, 2,4-DBP restricted the adhesion and invasion of P. aeruginosa to the A549 lung alveolar carcinoma cells. In addition, bactericidal assay with 2,4-DBP exhibited synergism with ampicillin to kill P. aeruginosa. Furthermore, our computational studies predicted that 2,4-DBP could bind to the P. aeruginosa quorum-sensing receptors LasR and RhlR. Collectively, these data suggest that 2,4-DBP can be exploited as a standalone drug or in combination with antibiotic(s) as an anti-virulence and anti-biofilm agent to combat the multidrug resistant P. aeruginosa infection.

Anti-quorum sensing and antibiofilm potential of Alternaria alternata, a foliar endophyte of Carica papaya, evidenced by QS assays and in-silico analysis

In the present study, secondary metabolites from an endophytic fungus, Alternaria alternata, colonizing Carica papaya, demonstrated antiquorum sensing properties against Pseudomonas aeruginosa. This study reports the antagonistic effects of fungal crude extract of A. alternata against the various quorum sensing (QS) associated virulent factors such as percentage decrease in production of pyocyanin, alginate, chitinase and rhamnolipid; significant decrease in proteases activity such as LasA protease activity, staphylolytic activity, Las B elastase; and a marked decrease in biofilm formation and associated factors such as exopolysaccharide (EPS) production and cell surface hydrophobicity (CSH). Further, motility pattern i.e., swimming and swarming was also found to be inhibited. This down regulation of QS and associated factors are further supported by in-silico analysis of interaction between QS receptor LasR and bioactive molecules viz., sulfurous acid, 2-propyl tridecyl ester and 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester present in fungal crude extract, found based on GCMS analysis, sketches the modulating ability of QS expression. This is the first report on an endophytic fungus of C. papaya having a role in QS inhibition against P. aeruginosa and lays a platform to explore further the endophytes for potent therapeutic agents in QS.

Towards a sustainable biobased industry - Highlighting the impact of extremophiles

The transition of the oil-based economy towards a sustainable economy completely relying on biomass as renewable feedstock requires the concerted action of academia, industry, politics and civil society. An interdisciplinary approach of various fields such as microbiology, molecular biology, chemistry, genetics, chemical engineering and agriculture in addition to cross-sectional technologies such as economy, logistics and digitalization is necessary to meet the future global challenges. The genomic era has contributed significantly to the exploitation of naturés biodiversity also from extreme habitats. By applying modern technologies it is now feasible to deliver robust enzymes (extremozymes) and robust microbial systems that are active at temperatures up to 120°C, at pH 0 and 12 and at 1000bar. In the post-genomic era, different sophisticated "omics" analyses will allow the identification of countless novel enzymes regardless of the lack of cultivability of most microorganisms. Furthermore, elaborate protein-engineering methods are clearing the way towards tailor-made robust biocatalysts. Applying environmentally friendly and efficient biological processes, terrestrial and marine biomass can be converted to high value products e.g. chemicals, building blocks, biomaterials, pharmaceuticals, food, feed and biofuels. Thus, further application of extremophiles has the potential to improve sustainability of existing biotechnological processes towards a greener biobased industry.

Enhancement of Exochitinase Production by Bacillus licheniformis AT6 Strain and Improvement of N-Acetylglucosamine Production

A strain producing chitinase, isolated from potato stem tissue, was identified as Bacillus licheniformis by biochemical properties and 16S RNA sequence analysis. Statistical experimental designs were used to optimize nine independent variables for chitinase production by B. licheniformis AT6 strain in submerged fermentation. Using Plackett-Burman design, (NH₄)₂SO₄, MgSO₄.7H₂O, colloidal chitin, MnCl₂ 2H₂O, and temperature were found to influence chitinase production significantly. According to Box-Behnken response surface methodology, the optimal fermentation conditions allowing maximum chitinase production were (in gram per liter): (NH₄)₂SO₄, 7; K₂HPO₄, 1; NaCl, 1; MgSO₄.7H₂O, 0.1; yeast extract, 0.5; colloidal chitin, 7.5; MnCl₂.2H₂O, 0.2; temperature 35 °C; pH medium 7. The optimization strategy led to a 10-fold increase in chitinase activity (505.26 ± 22.223 mU/mL versus 50.35 ± 19.62 mU/mL for control basal medium). A major protein band with a molecular weight of 61.9 kDa corresponding to chitinase activity was clearly detected under optimized conditions. Chitinase activity produced in optimized medium mainly releases N-acetyl glucosamine (GlcNAc) monomer from colloidal chitin. This enzyme also acts as an exochitinase with β-N-acetylglucosaminidase. These results suggest that B. licheniformis AT6 secreting exochitinase is highly efficient in GlcNAc production which could in turn be envisaged as a therapeutic agent or as a conservator against the alteration of several ailments.

Thermostable chitinase from Cohnella sp. A01: isolation and product optimization

Twelve bacterial strains isolated from shrimp farming ponds were screened for their growth activity on chitin as the sole carbon source. The highly chitinolytic bacterial strain was detected by qualitative cup plate assay and tentatively identified to be Cohnella sp. A01 based on 16S rDNA sequencing and by matching the key morphological, physiological, and biochemical characteristics. The cultivation of Cohnella sp. A01 in the suitable liquid medium resulted in the production of high levels of enzyme. The colloidal chitin, peptone, and K₂HPO₄ represented the best carbon, nitrogen, and phosphorus sources, respectively. Enzyme production by Cohnella sp. A01 was optimized by the Taguchi method. Our results demonstrated that inoculation amount and temperature of incubation were the most significant factors influencing chitinase production. From the tested values, the best pH/temperature was obtained at pH 5 and 70°C, with K_m and V_max values of chitinase to be 5.6mg/mL and 0.87μmol/min, respectively. Ag⁺, Co²⁺, iodoacetamide, and iodoacetic acid inhibited the enzyme activity, whereas Mn²⁺, Cu²⁺, Tweens (20 and 80), Triton X-100, and EDTA increased the same. In addition, the study of the morphological alteration of chitin treated by enzyme by SEM revealed cracks and pores on the chitin surface, indicating a potential application of this enzyme in several industries.

Molecular docking and site-directed mutagenesis of a Bacillus thuringiensis chitinase to improve chitinolytic, synergistic lepidopteran-larvicidal and nematicidal activities

Bacterial chitinases are useful in the biocontrol of agriculturally important pests and fungal pathogens. However, the utility of naturally occurring bacterial chitinases is often limited by their low enzyme activity. In this study, we constructed mutants of a Bacillus thuringiensis chitinase with enhanced activity based on homology modeling, molecular docking, and the site-directed mutagenesis of target residues to modify spatial positions, steric hindrances, or hydrophilicity/hydrophobicity. We first identified a gene from B. thuringiensis YBT-9602 that encodes a chitinase (Chi9602) belonging to glycosyl hydrolase family 18 with conserved substrate-binding and substrate-catalytic motifs. We constructed a structural model of a truncated version of Chi9602 (Chi9602_35-459) containing the substrate-binding domain using the homologous 1ITX protein of Bacillus circulans as the template. We performed molecular docking analysis of Chi9602_35-459 using di-N-acetyl-D-glucosamine as the ligand. We then selected 10 residues of interest from the docking area for the site-directed mutagenesis experiments and expression in Escherichia coli. Assays of the chitinolytic activity of the purified chitinases revealed that the three mutants exhibited increased chitinolytic activity. The ChiW50A mutant exhibited a greater than 60 % increase in chitinolytic activity, with similar pH, temperature and metal ion requirements, compared to wild-type Chi9602. Furthermore, ChiW50A exhibited pest-controlling activity and antifungal activity. Remarkable synergistic effects of this mutant with B. thuringiensis spore-crystal preparations against Helicoverpa armigera and Caenorhabditis elegans larvae and obvious activity against several plant-pathogenic fungi were observed.

Extremozymes--biocatalysts with unique properties from extremophilic microorganisms

Extremozymes are enzymes derived from extremophilic microorganisms that are able to withstand harsh conditions in industrial processes that were long thought to be destructive to proteins. Heat-stable and solvent-tolerant biocatalysts are valuable tools for processes in which for example hardly decomposable polymers need to be liquefied and degraded, while cold-active enzymes are of relevance for food and detergent industries. Extremophilic microorganisms are a rich source of naturally tailored enzymes, which are more superior over their mesophilic counterparts for applications at extreme conditions. Especially lignocellulolytic, amylolytic, and other biomass processing extremozymes with unique properties are widely distributed in thermophilic prokaryotes and are of high potential for versatile industrial processes.

Draft Genome Sequence of Bacillus thuringiensis Strain BrMgv02-JM63, a Chitinolytic Bacterium Isolated from Oil-Contaminated Mangrove Soil in Brazil

Here, we report the draft genome sequence and the automatic annotation of Bacillus thuringiensis strain BrMgv02-JM63. This genome comprises a set of genes involved in the metabolism of chitin and N-acetylglucosamine utilization, thus suggesting the possible role of this strain in the cycling of organic matter in mangrove soils.

Bacillus thuringiensis subsp. kurstaki HD1 as a factory to synthesize alkali-labile ChiA74∆sp chitinase inclusions, Cry crystals and spores for applied use

Background

The endochitinase ChiA74 is a soluble secreted enzyme produced by Bacillus thuringiensis that synergizes the entomotoxigenecity of Cry proteins that accumulate as intracellular crystalline inclusion during sporulation. The purpose of this study was to produce alkaline-soluble ChiA74∆sp inclusions in B. thuringiensis, and to determine its effect on Cry crystal production, sporulation and toxicity to an important agronomical insect, Manduca sexta. To this end we deleted the secretion signal peptide-coding sequence of chiA74 (i.e. chiA74∆sp) and expressed it under its native promoter (pEHchiA74∆sp) or strong chimeric sporulation-dependent cytA-p/STAB-SD promoter (pEBchiA74∆sp) in Escherichia coli, acrystalliferous B. thuringiensis (4Q7) and B. thuringiensis HD1.

Results

Based on mRNA analyses, up to ~9-fold increase in expression of chiA74∆sp was observed using the cytA-p/STAB-SD promoter. ChiA74∆sp (~70 kDa) formed intracellular inclusions that frequently accumulated at the poles of cells. ChiA74∆sp inclusions were dissolved in alkali and reducing conditions, similar to Cry crystals, and retained its activity in a wide range of pH (5 to 9), but showed a drastic reduction (~70%) at pH 10. Chitinase activity of E. coli-pEHchiA74∆sp was ~150 mU/mL, and in E. coli-pEBchiA74∆sp, 250 mU/mL. 4Q7-pEBchiA74∆sp and 4Q7-pEHchiA74∆sp had activities of ~127 mU/mL and ~41 mU/mL, respectively. The endochitinase activity in HD1-pEBchiA74∆sp increased 42x when compared to parental HD1 strain. HD1-pEBchiA74∆sp and HD1 harbored typical bipyramidal Cry inclusions, but crystals in the recombinant were ~30% smaller. Additionally, a 3x increase in the number of viable spores was observed in cultures of the recombinant strain when compared to HD1. Bioassays against first instar larvae of M. sexta with spore-crystals of HD1 or spore-crystal-ChiA74∆sp inclusions of HD1-pEBchiA74∆sp showed LC₅₀s of 67.30 ng/cm² and 41.45 ng/cm², respectively.

Conclusions

Alkali-labile ChiA74∆sp inclusion bodies can be synthesized in E. coli and B. thuringiensis strains. We demonstrated for the first time the applied utility of synthesis of ChiA74∆sp inclusions, Cry crystals and spores in the same sporangium of HD1, a strain used successfully worldwide to control economically significant lepidopteran pests of agriculture. Our findings will allow to us develop strategies to modify expression of ChiA74∆sp while maximizing Cry crystal synthesis in commercial strains of B. thuringiensis.

Isolation and characterization of Burkholderia rinojensis sp. nov., a non-Burkholderia cepacia complex soil bacterium with insecticidal and miticidal activities

Isolate A396, a bacterium isolated from a Japanese soil sample demonstrated strong insecticidal and miticidal activities in laboratory bioassays. The isolate was characterized through biochemical methods, fatty acid methyl ester (FAME) analysis, sequencing of 16S rRNA, multilocus sequence typing and analysis, and DNA-DNA hybridization. FAME analysis matched A396 to Burkholderia cenocepacia, but this result was not confirmed by 16S rRNA or DNA-DNA hybridization. 16S rRNA sequencing indicated closest matches with B. glumae and B. plantarii. DNA-DNA hybridization experiments with B. plantarii, B. glumae, B. multivorans, and B. cenocepacia confirmed the low genetic similarity (11.5 to 37.4%) with known members of the genus. PCR-based screening showed that A396 lacks markers associated with members of the B. cepacia complex. Bioassay results indicated two mechanisms of action: through ingestion and contact. The isolate effectively controlled beet armyworms (Spodoptera exigua; BAW) and two-spotted spider mites (Tetranychus urticae; TSSM). In diet overlay bioassays with BAW, 1% to 4% (vol/vol) dilution of the whole-cell broth caused 97% to 100% mortality 4 days postexposure, and leaf disc treatment bioassays attained 75% ± 22% mortality 3 days postexposure. Contact bioassays led to 50% larval mortality, as well as discoloration, stunting, and failure to molt. TSSM mortality reached 93% in treated leaf discs. Activity was maintained in cell-free supernatants and after heat treatment (60°C for 2 h), indicating that a secondary metabolite or excreted thermostable enzyme might be responsible for the activity. Based on these results, we describe the novel species Burkholderia rinojensis, a good candidate for the development of a biocontrol product against insect and mite pests.