High-level production of chitinase by multi-strategy combination optimization in Bacillus licheniformis

In view of the extensive potential applications of chitinase (ChiA) in various fields such as agriculture, environmental protection, medicine, and biotechnology, the development of a high-yielding strain capable of producing chitinase with enhanced activity holds significant importance. The objective of this study was to utilize the extracellular chitinase from Bacillus thuringiensis as the target, and Bacillus licheniformis as the expression host to achieve heterologous expression of ChiA with enhanced activity. Initially, through structural analysis and molecular dynamics simulation, we identified key amino acids to improve the enzymatic performance of chitinase, and the specific activity of chitinase mutant D116N/E118N was 48% higher than that of the natural enzyme, with concomitant enhancements in thermostability and pH stability. Subsequently, the expression elements of ChiA(D116N/E118N) were screened and modified in Bacillus licheniformis, resulting in extracellular ChiA activity reached 89.31 U/mL. Further efforts involved the successful knockout of extracellular protease genes aprE, bprA and epr, along with the gene clusters involved in the synthesis of by-products such as bacitracin and lichenin from Bacillus licheniformis. This led to the development of a recombinant strain, DW2△abelA, which exhibited a remarkable improvement in chitinase activity, reaching 145.56 U/mL. To further improve chitinase activity, a chitinase expression frame was integrated into the genome of DW2△abelA, resulting in a significant increas to 180.26 U/mL. Optimization of fermentation conditions and medium components further boosted shake flask enzyme activity shake flask enzyme activity, achieving 200.28 U/mL, while scale-up fermentation experiments yielded an impressive enzyme activity of 338.79 U/mL. Through host genetic modification, expression optimization and fermentation optimization, a high-yielding ChiA strain was successfully constructed, which will provide a solid foundation for the extracellular production of ChiA.

TipB, a novel cell wall hydrolase, is required for efficient conjugative transfer of pXO16 from Bacillus thuringiensis sv. israelensis

pXO16, a large plasmid from Bacillus thuringiensis serovar israelensis, exhibits unique features. Not only is pXO16 able to transfer at high frequencies within few minutes, but it is also able to transfer among virtually all members of the Bacillus cereus group. Among the proteins encoded in the tip transfer locus of pXO16, TipB displays an atypical organization compared to known conjugative cell wall hydrolases with the large central soluble lytic transglycosylase (SLT) domain missing from the protein. We constructed a tipB deletion mutant which led to significant reduction in transfer efficiencies in both liquid and filter mating. The initial transfer frequencies could be restored when complementing tipB in trans thus showing the TipB implication in pXO16 conjugative transfer. Additionally, truncated versions of TipB were expressed in Escherichia coli to assess the protein lytic activity. When applied exogenously, TipB-2TM, in which the two N-terminal TM domains were removed, yielded a decrease of ca. 40% in optical density of B. thuringiensis sv. israelensis, a lytic activity that could partially be explained by the C-terminal CHAP-like domain. These results confirm TipB conjugative hydrolase function and provide new insights into pXO16 unique conjugative apparatus.

Bisphenol A degradation pathway and associated metabolic networks in Escherichia coli harboring the gene encoding CYP450

Although bisphenol A (BPA) can be transformed by CYP450, the metabolic networks involved in regulating the transformation processes are not clear. In this study, Escherichia coli harboring the gene encoding CYP450 was used as a model to elucidate the BPA degradation pathway and the associated metabolic network using a proteomic approach. The results showed that CYP450 promotes the transformation of BPA, generating 1,2-bis(4-hydroxyphenyl)-2-propanol and 2,2-bis(4-hydroxyphenyl)-1-propanol, with hydroquinone and 4-(2-hydroxypropan-2-yl)phenol formed in another pathway. The DNA adducts formed by 1,4-benzoquinone were reduced, and CYP450 played a positive role in cellular homeostasis by promoting the transformation of BPA and mismatch repair. An increase in the synthesis of cell membrane lipids was observed after dislodging BPA. BPA disturbed folate metabolism by decreasing the abundance of dihydrofolate reductase, which inhibited microbial metabolism in the absence of CYP450. The findings of this study revealed the molecular mechanism associated with the metabolic network responsible for pollutant tolerance and degradation.

A Genome-Centric Approach Reveals a Novel Glycosyltransferase from the GA A07 Strain of Bacillus thuringiensis Responsible for Catalyzing 15-O-Glycosylation of Ganoderic Acid A

Strain GA A07 was identified as an intestinal Bacillus bacterium of zebrafish, which has high efficiency to biotransform the triterpenoid, ganoderic acid A (GAA), into GAA-15-O-β-glucoside. To date, only two known enzymes (BsUGT398 and BsUGT489) of Bacillus subtilis ATCC 6633 strain can biotransform GAA. It is thus worthwhile to identify the responsible genes of strain GA A07 by whole genome sequencing. A complete genome of strain GA A07 was successfully assembled. A phylogenomic analysis revealed the species of the GA A07 strain to be Bacillus thuringiensis. Forty glycosyltransferase (GT) family genes were identified from the complete genome, among which three genes (FQZ25_16345, FQZ25_19840, and FQZ25_19010) were closely related to BsUGT398 and BsUGT489. Two of the three candidate genes, FQZ25_16345 and FQZ25_19010, were successfully cloned and expressed in a soluble form in Escherichia coli, and the corresponding proteins, BtGT_16345 and BtGT_19010, were purified for a biotransformation activity assay. An ultra-performance liquid chromatographic analysis further confirmed that only the purified BtGT_16345 had the key biotransformation activity of catalyzing GAA into GAA-15-O-β-glucoside. The suitable conditions for this enzyme activity were pH 7.5, 10 mM of magnesium ions, and 30 °C. In addition, BtGT_16345 showed glycosylation activity toward seven flavonoids (apigenein, quercetein, naringenein, resveratrol, genistein, daidzein, and 8-hydroxydaidzein) and two triterpenoids (GAA and antcin K). A kinetic study showed that the catalytic efficiency (kcat/KM) of BtGT_16345 was not significantly different compared with either BsUGT398 or BsUGT489. In short, this study identified BtGT_16345 from B. thuringiensis GA A07 is the catalytic enzyme responsible for the 15-O-glycosylation of GAA and it was also regioselective toward triterpenoid substrates.

Benzo(a)pyrene degradation by cytochrome P450 hydroxylase and the functional metabolism network of Bacillus thuringiensis

The relationship between benzo(a)pyrene biodegradation and certain target biomolecules has been investigated. To regulate the degradation process, the associated metabolism network must be clarified. To this end, benzo(a)pyrene degradation, carbon substrate metabolism and exometabolomic mechanism of Bacillus thuringiensis were analyzed. Benzo(a)pyrene was degraded through hydroxylation catalyzed by cytochrome P450 hydroxylase. After the treatment of 0.5 mg L^-1 of benzo(a)pyrene by 0.2 g L^-1 of cells for 9 d, biosorption and degradation efficiencies were measured at approximately 90% and 80%, respectively. During this process, phospholipid synthesis, glycogen, asparagine, arginine, itaconate and xylose metabolism were significantly downregulated, while glycolysis, pentose phosphate pathway, citrate cycle, amino sugar and nucleotide sugar metabolism were significantly upregulated. These findings offer insight into the biotransformation regulation of polycyclic aromatic hydrocarbons.

Growth medium-dependent antimicrobial activity of early stage MEP pathway inhibitors

The in vivo microenvironment of bacterial pathogens is often characterized by nutrient limitation. Consequently, conventional rich in vitro culture conditions used widely to evaluate antibacterial agents are often poorly predictive of in vivo activity, especially for agents targeting metabolic pathways. In one such pathway, the methylerythritol phosphate (MEP) pathway, which is essential for production of isoprenoids in bacterial pathogens, relatively little is known about the influence of growth environment on antibacterial properties of inhibitors targeting enzymes in this pathway. The early steps of the MEP pathway are catalyzed by 1-deoxy-d-xylulose 5-phosphate (DXP) synthase and reductoisomerase (IspC). The in vitro antibacterial efficacy of the DXP synthase inhibitor butylacetylphosphonate (BAP) was recently reported to be strongly dependent upon growth medium, with high potency observed under nutrient limitation and exceedingly weak activity in nutrient-rich conditions. In contrast, the well-known IspC inhibitor fosmidomycin has potent antibacterial activity in nutrient-rich conditions, but to date, its efficacy had not been explored under more relevant nutrient-limited conditions. The goal of this work was to thoroughly characterize the effects of BAP and fosmidomycin on bacterial cells under varied growth conditions. In this work, we show that activities of both inhibitors, alone and in combination, are strongly dependent upon growth medium, with differences in cellular uptake contributing to variance in potency of both agents. Fosmidomycin is dissimilar to BAP in that it displays relatively weaker activity in nutrient-limited compared to nutrient-rich conditions. Interestingly, while it has been generally accepted that fosmidomycin activity depends upon expression of the GlpT transporter, our results indicate for the first time that fosmidomycin can enter cells by an alternative mechanism under nutrient limitation. Finally, we show that the potency and relationship of the BAP-fosmidomycin combination also depends upon the growth medium, revealing a striking loss of BAP-fosmidomycin synergy under nutrient limitation. This change in BAP-fosmidomycin relationship suggests a shift in the metabolic and/or regulatory networks surrounding DXP accompanying the change in growth medium, the understanding of which could significantly impact targeting strategies against this pathway. More generally, our findings emphasize the importance of considering physiologically relevant growth conditions for predicting the antibacterial potential MEP pathway inhibitors and for studies of their intracellular targets.

Isolation and purification of Bacillus thuringiensis var. israelensis IМV В-7465 peptidase with specificity toward elastin and collagen

Peptidase of Bacillus thuringiensis var. israelensis IМV В-7465 was isolated from culture supernatant using consecutive fractionations by an ammonium sulphate (60% saturation), ion-exchange chromatography and gel-filtration on the TSK-gels Toyoperl HW-55 and DEAE 650(M). Specific elastase (442 U∙mg of protein-1) and collagenase (212.7 U∙mg of protein-1) activities of the purified enzyme preparation were 8.0- and 6.1-fold, respectively higher than ones of the culture supernatant. Peptidase yields were 33.5% for elastase activity and 30.1% for collagenase activity. It was established that the enzyme is serine metal-dependent alkaline peptidase with Mr about 37 kDa. Maximal hydrolysis of elastin and collagen occurs at the optimum pH 8.0 and t° – 40 and 50 °С, respectively. The purified preparation has high stability at pH in the range of 7.0 to 10.0 and 40-50 °С.

Bacillus thuringiensis peptidoglycan hydrolase SleB171 involved in daughter cell separation during cell division

Whole-genome analyses have revealed a putative cell wall hydrolase gene (sleB171) that constitutes an operon with two other genes (ypeBandyhcN) of unknown function inBacillus thuringiensisBMB171. The putative SleB171 protein consists of 259 amino acids and has a molecular weight of 28.3 kDa. Gene disruption ofsleB171in the BMB171 genome causes the formation of long cell chains during the vegetative growth phase and delays spore formation and spore release, although it has no significant effect on cell growth and the ultimate release of the spores. The inseparable vegetative cells were nearly restored through the complementation ofsleB171expression. Real-time quantitative polymerase chain reaction analysis revealed thatsleB171is mainly active in the vegetative growth phase, with a maximum activity at the early stationary growth phase. Western blot analysis also confirmed thatsleB171is preferentially expressed during the vegetative growth phase. These results demonstrated that SleB171 plays an essential role in the daughter cell separation during cell division.

Down-regulation of a novel ABC transporter gene (Pxwhite) is associated with Cry1Ac resistance in the diamondback moth, Plutella xylostella (L.)

Biopesticides or transgenic crops based on Cry toxins from the soil bacterium Bacillus thuringiensis (Bt) effectively control agricultural insect pests. The sustainable use of Bt biopesticides and Bt crops is threatened, however, by the development of Cry resistance in the target pests. The diamondback moth, Plutella xylostella (L.), is the first pest that developed resistance to a Bt biopesticide in the field, and a recent study has shown that the resistance of P. xylostella to Cry1Ac is caused by a mutation in an ATP-binding cassette (ABC) transporter gene (ABCC2). In this study, we report that down-regulation of a novel ABC transporter gene from ABCG subfamily (Pxwhite) is associated with Cry1Ac resistance in P. xylostella. The full-length cDNA sequence of Pxwhite was cloned and analyzed. Spatial-temporal expression detection revealed that Pxwhite was expressed in all tissues and developmental stages, and highest expressed in Malpighian tubule tissue and in egg stage. Sequence variation analysis of Pxwhite indicated the absence of constant non-synonymous mutations between susceptible and resistant strains, whereas midgut transcript analysis showed that Pxwhite was remarkably reduced in all resistant strains and further reduced when larvae of the moderately resistant SZ-R strain were subjected to selection with Cry1Ac toxin. Furthermore, RNA interference (RNAi)-mediated suppression of Pxwhite gene expression significantly reduced larval susceptibility to Cry1Ac toxin, and genetic linkage analysis confirmed that down-regulation of Pxwhite gene is tightly linked to Cry1Ac resistance in P. xylostella. To our knowledge, this is the first report indicating that Pxwhite gene is involved in Cry1Ac resistance in P. xylostella.

Characterization of regulatory regions involved in the inducible expression of chiB in Bacillus thuringiensis

Expression of the chiB gene from Bacillus thuringiensis Bti75 was defined as inducible by the use of transcriptional fusions with the bgaB reporter gene. The transcription start site of the chiB gene was identified as the C base located 132 base pairs upstream of the start codon. Analysis of 5' and 3' deletions of the chiB promoter region revealed that the sequence from position -192 to +36 with respect to the transcription start site was necessary for wild-type levels of inducible expression of the chiB gene. The minimal promoter region for the expression of chiB gene was identified as the sequence from position -100 to +12. Furthermore, a 16-bp sequence (designated dre) downstream of the minimal promoter region of chiB was shown to be required for chitin induction. To confirm the function of this 16-bp sequence, 25 base substitutions were introduced into the dre site. Most of the mutations resulted in constitutive expression, or the efficiency of induction decreased. All mutations identified the dre sequence as a critical site for the inducible expression of chiB. In addition, the dre site was shown to interact with a sequence-specific DNA binding factor of strain Bti75 cultured in the absence of the inducer.

[Influence of coordination compounds of germanium (IV) and stannum (IV) on activity of some microbial enzymes with glycolytic and proteolytic action]

Influence of coordinative compounds of germanium (IV) and stanum (IV) (complexes of germanium (IV) with nicotinamide (Nad) [GeCl2(Nad)4]Cl2 (1) and complexes of stanum (IV) with 2-hydroxybenzoilhydrazone 4-dimetylaminobenzaldehide (2-OH-HBdb) [SnCl4(2-OH-Bdb-H)] (2), 3-hydroxy-2-naphtoilhydrazone 2-hydroxynaphtaldehide (3-OH-H2Lnf) [SnCl3(3-OH-HLnf)] (3) and izonicotinoilhydrazone 2-hydroxyibenzaldehide [SnCl3 (Is·H)] (4) on activity of peptidases 1 and 2 Bacillus thuringiensis, α-L-rhamnosidase Cryptococcus albidus, Eupenicillium erubescens and α-amylase Aspergillus flavus var. oryzae. Results testify that all studied compounds differ on their influence on activity of the enzymes tested: significantly don't change elastolytic activity of peptidases 1 and 2 B. thuringiensis, completely inhibit A. flavus var. oryzae amylase, activate or oppress of α-L-rhamnosidase C. albidus and E. erubescens. Considerable differences in compounds (3, 4) on activity observed in case of the last. It's possible that peculiarity of influence (1) in compare with (2-4) is connected with existence of different central atoms of complexants: germanium (IV) (1) and stanum (IV) (2-4). A certain analogy in oppression of C. albidus α-L-rhamnosidase by compounds (1) and (4) can explain with presence of a pyridinic ring at molecules of their ligands. The less activsty displayed compound (2) with coordinative knot {SnCl4ON}. Nature of compounds (3, 4) activity was absolutely different: essential increase of activity of C. albidus α-L-rhamnosidase and full oppression of E. erubescens α-L-rhamnosidase by compound (3), while the action of compound (4) was feed back. Taking into account identical coordination knot {SnCl3O2N} the major role in this case play change of a hydrazide fragment in molecules of their ligands.

Enzymatic hydrolysis of molecules associated with bacterial quorum sensing using an acyl homoserine lactonase from a novel Bacillus thuringiensis strain

N-acyl homoserine lactones are key components of quorum sensing, the bacterial communication system. This communication mechanism regulates the expression of genes, including those involved in virulence and biofilm formation. This system can be interrupted by the action of enzymes that hydrolyze the signaling molecules. In this work, we studied the enzymatic properties of a recombinant AHL-lactonase from Bacillus thuringiensis strain 147-11516, using substrates with acyl chains of different length (C4-HSL, C6-HSL, C7-HSL, C8-HSL and C10-HSL), we also investigated the effect of pH (5.0–9.0), temperature (20–70 °C), concentration of monovalent, divalent and trivalent metals ions (0.2 and 2.0 mM) and EDTA. The results showed that the recombinant AHL-lactonase had biological activity in alkaline pH conditions (8.0) and high temperature (47 % of hydrolyzed substrate at 60 °C). The recombinant AHL-lactonase has activity on substrates with different acyl chain length. However, the activity of the recombinant enzyme was decreased in the two concentrations of all metal ions evaluated but was not inhibited by EDTA. The affinity of the enzyme for all substrates tested and its performance, in the evaluated conditions, suggest that the AHL-lactonase from B. thuringiensis strain 147-11516 could be used as a strategy for disruption of the Gram-negative bacteria communication system under normal and challenging conditions.

[Characterization of recombinant L-isoleucine-4-hydroxylase from Bacillus thuringiensis and its application in 4hydroxyisoleucine biosynthesis]

OBJECTIVE

L-isoleucine-4-hydroxylase (IDO) encoding gene ido from Bacillus thuringiensis TCCC 11826 was cloned and expressed, followed by enzyme characterization. In addition, recombinant strain was tested for its 4-Hydroxyisoleucine (4-HIL) biotransformation.

METHODS

Ido gene was amplified from B. thuringiensis TCCC 11826 genomic DNA and expressed in BL-IDO. Recombinant IDO was extracted, purified and characterized. Recombinant strain used for biotransformation of 4-HIL was constructed.

RESULTS

Composed of 723 nucleotides encoding 240 amino acids (sharing 97.47% and 97.91% identities with that of B. thuringiensis 2-e-2), ido gene was cloned from B. thuringiensis TCCC 11826. The recombinant IDO contained a His1-X-Asp/Glu-Xn-His2 motif that is specific for Fe(II)/alpha-ketoglutarate-dependent hydroxylases and catalyzed L-isoleucine to 4-HIL. Normal hyperbolic kinetics was observed with L-Ile in the reaction by recombinant IDO. Lineweaver-Burk treatment of the data yielded apparent Km and the Vmax was 0.18 mmol/L and 2.10 micromol/min/mg, respectively. The optimum temperature and pH for the recombinant IDO was 35 degrees C and 7.0 respectively; moreover, the relative activity of the enzyme remain 85.10% after 5 h incubation at 35 degrees C. In all, recombinant strain harboring ido transformed 89.28% of L-isoleucine to 4-HIL.

CONCLUSION

In this study, an ido (Accession No. KC884243) with novel sequence was isolated and enzymatic characteristics of recombinant IDO was systematically analyzed. In addition, we successfully achieved the biotransformation of 4-HIL from L-isoleucine. This work will lay theoretical foundation and practical basis on the microbial manufacture technology of 4-HIL and other amino acid derivatives. This work will lay theoretical foundation and practical basis on the microbial manufacture technology of 4-HIL and other amino acid derivatives.

[Enhancement of enzyme activity and thermostability of N-acylhomoserine lactonase by site-directed mutagenesis]

OBJECTIVE

To enhance enzymatic activity and thermostability of N-acylhomoserine lactonase (AiiA).

METHODS

We performed site-directed mutagenesis based on AiiA homologous 3-D protein structure, and analyzed enzymatic activity and thermostability of both wild type and mutated AiiA.

RESULTS

The wild type AiiA lost its N-acylhomoserine lactone (AHL) degrading activity after being incubated at 45 degrees C for 30 min or after being stored at 4 degrees C for 5 days. By comparison, the AHL-degrading activities of three types of mutated AiiA (N65K, T195R, and A206E) were enhanced, and their storage periods at 4 degrees C were extended to 7 days. In addition, the N65K mutant acquired higher temperature tolerance with remain of more than 45% of its enzymatic activity after being incubated at 45 degrees C and 5.0% enzymatic activity after being incubated at 55 degrees C as compared to the wild type.

CONCLUSION

Molecular modulation by site-directed mutagenesis could significantly improve enzymatic activity and thermostability of AiiA.

[Complexes of cobalt (II, III) with derivatives of dithiocarbamic acid--effectors of peptidases of Bacillus thuringiensis and alpha-L-rhamnozidase of Eupenicillium erubescens and Cryptococcus albidus]

The influence of cobalt (II, III) coordinative compounds with derivatives of dithiocarbamic acid on Bacillus thuringiensis IMV B-7324 peptidases with elastase and fibrinolytic activity and Eupenicillium erubescens and Cryptococcus albidus alpha-L-rhamnosidases have been studied. Tested coordinative compounds of cobalt (II, III) on the basis of their composition and structure are presented by 6 groups: 1) tetrachlorocobaltates (II) of 3,6-di(R,R')-iminio-1,2,4,5-tetratiane--(RR')2Ditt[CoCl4]; 2) tetrabromocobaltates (II) of 3,6-di(R,R')-iminio-1,2,4,5-tetratiane--(RR')2Ditt[CoBr4]; 3) isothiocyanates of tetra((R,R')-dithiocarbamatoisothiocyanate)cobalt (II)--[Co(RR'Ditc)4](NCS)2]; 4) dithiocarbamates of cobalt (II)--[Co(S2CNRR')2]; 5) dithiocarbamates of cobalt (III)--[Co(S2CNRR')3]; 6) molecular complexes of dithiocarbamates of cobalt (III) with iodine--[Co(S2CNRR')3] x 2I(2). These groups (1-6) are combined by the presence of the same complexing agent (cobalt) and a fragment S2CNRR' in their molecules. Investigated complexes differ by a charge of intrinsic coordination sphere: anionic (1-2), cationic (3) and neutral (4-6). The nature of substituents at nitrogen atoms varies in each group of complexes. It is stated that the studied coordination compounds render both activating and inhibiting effect on enzyme activity, depending on composition, structure, charge of complex, coordination number of complex former and also on the enzyme and strain producer. Maximum effect is achieved by activating of peptidases B. thuringiensis IMV B-7324 with elastase and fibrinolytic activity. So, in order to improve the catalytic properties of peptidase 1, depending on the type of exhibited activity, it is possible to recommend the following compounds: for elastase--coordinately nonsaturated complexes of cobalt (II) (1-4) containing short aliphatic or alicyclic substituents at atoms of nitrogen and increasing activity by 17-100% at an average; for fibrinolytic--neutral dithiocarbamates of cobalt (II, III) (4-5) (by 29-199%). For increasing the fibrinolytic activity of peptidase it is better to use dibenzyl- or ethylphenyldithiocarbamates of cobalt (III), which increase activity by 15-40% at an average. The same complexes, and also compound {(CH2)6}2Ditt[CoCl4] make an activating impact on alpha-L-rhamnosidase C. albidus (by 10-20%).

Purification and characterization of keratinase from feather degrading bacterium useful for mosquito control--a new report

Every day, food processing industries release wastes, which are environmental menance. Chicken feathers have been discarded in bulk as waste from poultry industries, globally. Degrading these wastes, as unused disposals, without acquiring any additional benefits has led to an idea to develop a new technology. We have reported earlier that Bacillus thuringiensis serovar israelensis (Bti) can be used for biodegradation of feather waste for biopesticide production. In the present study, purification and characterization of keratinase from feather degrading bacterium (Bti) is reported. Protein precipitate obtained at Ammonium sulphate saturation at 60% level and Sephacryl S-200 column chromatography resulted in 2.3 and 11.68 fold purification of the enzyme respectively. The purity was revealed in SDS-PAGE by a single band of molecular weight of 40 kDa and it was characterized. The optimum pH of the enzyme shifted to a more neutral range (6.0-8.0) with the highest activity (7.0). The optimum temperature of the reaction was determined to be 30ºC. The keratinase enzyme retained 51% residual activity (303 U/mg protein) at 70ºC (60 min) and the half-lives of the enzyme were 130 minutes at 40ºC, 90 min at 50ºC and of 60 min at 70ºC, respectively. Keratinase activity was enhanced by calcium and magnesium ions while EDTA, PMSF, β- mercaptoethanol and manganese inhibited the activity. This is the first report investigating the keratinase from Bti degraded chicken feathers for the bio-synthesis of mosquitocidal toxins.

The glycosyltransferase involved in thurandacin biosynthesis catalyzes both O- and S-glycosylation

The S-glycosyltransferase SunS is a recently discovered enzyme that selectively catalyzes the conjugation of carbohydrates to the cysteine thiol of proteins. This study reports the discovery of a second S-glycosyltransferase, ThuS, and shows that ThuS catalyzes both S-glycosylation of the thiol of cysteine and O-glycosylation of the hydroxyl group of serine in peptide substrates. ThuS-catalyzed S-glycosylation is more efficient than O-glycosylation, and the enzyme demonstrates high tolerance with respect to both nucleotide sugars and peptide substrates. The biosynthesis of the putative products of the thuS gene cluster was reconstituted in vitro, and the resulting S-glycosylated peptides thurandacin A and B exhibit highly selective antimicrobial activity toward Bacillus thuringiensis.

New insights into the binding and catalytic mechanisms of Bacillus thuringiensis lactonase: insights into B. thuringiensis AiiA mechanism

The lactonase enzyme (AiiA) produced by Bacillus thuringiensis serves to degrade autoinducer-1 (AI-1) signaling molecules in what is an evolved mechanism by which to compete with other bacteria. Bioassays have been previously performed to determine whether the AI-1 aliphatic tail lengths have any effect on AiiA's bioactivity, however, data to date are conflicting. Additionally, specific residue contributions to the catalytic activity of AiiA provide for some interesting questions. For example, it has been proposed that Y194 serves to provide an oxyanion hole to AI-1 which is curious given the fact the substrate spans two Zn(2+) ions. These ions might conceivably provide enough charge to promote both ligand stability and the carbonyl activation necessary to drive a nucleophilic attack. To investigate these questions, multiple molecular dynamics simulations were performed across a family of seven acylated homoserine lactones (AHL) along with their associated intermediate and product states. Distance analyses and interaction energy analyses were performed to investigate current bioassay data. Our simulations are consistent with experimental studies showing that AiiA degrades AHLs in a tail length independent manner. However, the presence of the tail is required for activity. Also, the putative oxyanion hole function of Y194 toward the substrate is not observed in any of the reactant or product state simulation trajectories, but does seem to show efficacy in stabilizing the intermediate state. Last, we argue through ionization state analyses, that the proton shuttling necessary for catalytic activity might be mediated by both water and substrate-based intra-molecular proton transfer. Based on this argument, an alternate catalytic mechanism is proposed.

[Physico-chemical properties of Bacillus thuringiensis IMV B-7324 fibrinolytic peptidase]

Investigations of physico-chemical properties of the Bacillus thuringiensis IMV B-7324 fibrinolytic peptidase showed that optimal activity of enzyme displayed at pH 10.0 and temperature 60 degrees C. Stability of peptidase retained in the range of pH from 6.0 to 11.0 and temperature from 20 to 50 degrees C over 1 h. Inhibition of fibrinolytic peptidase activity by ethylene glycol tetraacetic acid (EGTA) and tetrasodium salt of ethylenediaminetetraacetic acid (trilon B) indicates the belonging of this enzyme to the group of metallopeptidases. It was established that cations Ag+, Mg2+ and Ba2+ increased the fibrinolytic activity by 40 %, 25 % and 30 %, respectively, but Ca2+, Zn2+, Cu2+, Pb2+ and Hg2+ reduced it by 30-60%. Several of studied anions (F-, Br-, SO2-, S2O(2-)3, AsO(3-)4, NO-(3) and NO2(-) inhibit the activity of B. thuringiensis IMV B-7324 fibrinolytic peptidase by 25-100%.

[Effect of clpP disruption on alkaline sensitivity of Bacillus thuringiensis]

OBJECTIVE

We compared alkaline tolerance between Bacillus thuringiensis (Bt) and B. subtilis (Bs) and to determine the effect on growth when the clpP gene encoding caseinolytic protease is disrupted after alkaline shock.

METHODS

B. thuringiensis HD73 mutant with the deletion of clpP gene was constructed by homologous recombination. The effects of clpP deletion on the growth after alkaline shock, sporulation and germination were analyzed.

RESULTS

Bt can recover growth from alkaline shock when the medium pH was between 8.9 and 9.1 whereas that was between 8.2 and 8.4 for Bs. Bt tolerated alkaline more than Bs, leading Bt to adapt in alkaline environment of the midgut as a pathogen of insect. Deletion of clpP gene had no influence on sporulation and germination. The clpP mutant grew slower than Bt HD73 in the LB medium in addition to NaOH of 30 mmol/L. It indicates that the ClpP plays an important role in the alkaline tolerance of Bt strain.

[Purification and physicochemical properties of Bacillus thuringiensis IMB B-7324 peptidase with elastolytic and fibrinolytic activity]

The scheme of isolation and purification of Bacillus thuringiensis IMV B-7324 peptidase has been developed. This scheme includes ammonium sulfate precipitation and chromatography on neutral and charged TSK-gels. It was found that the enzyme hydrolyzes elastin and fibrin. The molecular weight is 26 kDa. It was shown that the enzyme is an alkaline serine peptidase. The optimal pH of hydrolysis of elastin and fibrin were 9.0 and 10.0, respectively. The optimal temperature of elastin and fibrin hydrolysis are 40 and 50 degrees C, respectively. The high stability of the purified preparation in the studied range of pH and temperature was shown. The stabilizing effect of zinc at a concentration of 1 mM on the elastase activity, and the inhibitory effect of other divalent cations under study have been established. The investigated chloride and acetate anions reduced activity by 20%, while phosphate anions increased activity by 15-30%.

Anti-fungi activities of Bacillus thuringiensis H3 chitinase and immobilized chitinase particles and their effects to rice seedling defensive enzymes

The chitinase producing bacterium H3 strain was screened from nature with the selective medium and was identified as Bacillus thuringiensis. The purpose of this investigation is to study the antifungi activity of Bacillus thuringiensis H3 chitinase and its immobilized particles, and the effects on growth of rice seedlings and activities of defensive enzymes. The rice seedlings qualities and several defense enzymes activity were measured after rice seedlings were treated by free chitinase and immobilized chitinase particles. The results show that the height and dry weight of the rice considerably increased in comparison with the control. Bacillus thuringiensis H3 chitinase and it's immobilized particles significantly inhibit several pathogenic fungi, and the anti-fungi rates of immobilized chitinase particles on Pyricularia grisea, Thantephorus cucumris, Fusarium vasinfectum, Fusarium gramineum, Fusarium oxysporum are 72.2%, 62.6%, 44.6%, 50.0%, 55.8%, respectively. Phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities of the rice seedling were significantly increased when it was treated by free chitinase and immobilized chitinase particles. From the results it could be concluded that Bacillus thuringiensis H3 free chitinase and immobilized chitinase particles can inhibit several pathogenic fungi and induce rice seedlings defense enzymes activity changes.

[Isolation of Bacillus thuringiensis IMV B-7324 fibrinolytic peptidase]

Fibrinolytic peptidase of Bacillus thuringiensis IMV B-7324 was isolated by ammonium sulfate fractionation, gel-filtration and ion exchange chromatography on TSK-gels--Toyopearl HW-55 and DEAE 650 (M). Fibrinolytic activity of the purified enzyme was 87.9 U/mg of protein that was 19.9 times higher compared with the supernatant cultural liquid, the yield on its activity reached 31%. The gel-filtration on Sepharose 6B and by SDS-PAGE electrophoresis demonstrated the homogeneity of the purified fibrinolytic peptidase, which molecular weight was approximately 24 kDa.

Impact of transgenic cotton varieties on activity of enzymes in their rhizosphere

The impact of five Bacillus thuringiensis (Bt) cotton varieties and their respective isogenic non-Bt(NBt) isolines (ANKUR-2534, MECH-6304, RCH-317, ANKUR-651 and MECH-6301) was assessed on the key soil enzymes i.e., dehydrogenase, alkaline phosphatase and urease in their rhizosphere at four growth stages of the crop, namely vegetative, flowering, bolling and harvesting. These varieties were grown on farmer's field in villages 22 miles and 24 miles of Ganganagar District of Rajasthan State in India. Results showed that dehydrogenase, alkaline phosphatase and urease activities were higher in rhizosphere of Bt isolines as compared to NBt isolines of all the varieties. Except phosphatase, differences in dehydrogenase and urease activities in rhizosphere of Bt and NBt isolines of all five varieties were significant (P < 0.05). Maximum enhancement in the three enzymes activities was observed in MECH-6304 Bt isoline rhizosphere. Maximum and minimum activities of dehydrogenase and urease were observed in MECH-6304 and RCH-317 Bt isolines, respectively, whereas phosphatase activity was maximum and minimum in MECH-6304 and ANKUR-651 Bt isolines, respectively. Maximum dehydrogenase and urease activities were observed at boll formation and minimum at flowering and harvesting stage, respectively, while maximum phosphatase activity was observed at vegetative stage and minimum at harvesting stage. In conclusion, all the studied Bt isolines of cotton varieties showed no adverse effect on dehydrogenase, alkaline phosphatase and urease activities in the rhizosphere.

The direct repeat sequence upstream of Bacillus chitinase genes is cis-acting elements that negatively regulate heterologous expression in E. coli

To explore the influence of the direct repeat sequence (DRS) in Bacillus chitinase genes on heterogonous expression in Escherichia coli, we cloned and sequenced the entire open reading frame (ORF) and upstream sequences of the chitinase B (chiB) and chitinase MY75 (chiMY75) from Bacillus thuringiensis and Bacillus licheniformis. A pair of 8-bp DRS was found upstream of each chi gene. Chi ORFs with a series of truncated DRS were cloned and transformed into E. coli XL-Blue. The activity of the transformants without the DRS were significantly higher in chitinase assays than transformants containing the DRS. SDS-PAGE showed that part and full deletion of the DRS increased chi gene expression by approximately 1.7 and 3.8-fold, respectively. Northern blotting revealed deletion of the DRS regions increased chiB and chiMY75 mRNA expression. Specific binding of DNA-binding factors in the E. coli cell lyaste was observed to both the chiB and chiMY75 promoter regions and DRS elements. This is the first investigation to demonstrate that heterologous expression of Bacillus chi genes in E. coli is negatively regulated by their upstream DRS regions, which act as cis-acting elements.

Large crystal toxin formation in chromosomally engineered Bacillus thuringiensis subsp. aizawai due to σE accumulation

Seven distinct Bacillus thuringiensis subsp. aizawai integrants were constructed that carried the chitinase (chiBlA) gene from B. licheniformis under the control of the cry11Aa promoter and terminator with and without p19 and p20 genes. The toxicity of B. thuringiensis subsp. aizawai integrants against second-instar Spodoptera litura larvae was increased 1.8- to 4.6-fold compared to that of the wild-type strain (BTA1). Surprisingly, the enhanced toxicity in some strains of B. thuringiensis subsp. aizawai integrants (BtaP19CS, BtaP19CSter, and BtaCAT) correlated with an increase in toxin formation. To investigate the role of these genes in toxin production, the expression profiles of the toxin genes, cry1Aa and chiBlA, as well as their transcriptional regulators (sigK and sigE), were analyzed by quantitative real-time RT-PCR (qPCR) from BTA1, BtaP19CS, and BtaCAT. Expression levels of cry1Aa in these two integrants increased about 2- to 3-fold compared to those of BTA1. The expression of the transcription factor sigK also was prolonged in the integrants compared to that of the wild type; however, sigE expression was unchanged. Western blot analysis of σ(E) and σ(K) showed the prolonged accumulation of σ(E) in the integrants compared to that of BTA1, resulting in the increased synthesis of pro-σ(K) up to T(17) after the onset of sporulation in both BtaP19CS and BtaCAT compared to that of T(13) in BTA1. The results from qPCR indicate clearly that the cry1Aa promoter activity was influenced most strongly by σ(E), whereas cry11Aa depended mostly on σ(K). These results on large-crystal toxin formation with enhanced toxicity should provide useful information for the generation of strains with improved insecticidal activity.

Heterologous overexpression, purification, and in vitro characterization of AHL lactonases

Quorum-quenching enzymes are useful as biochemical tools and possible therapeutic proteins. One of the best-characterized families of these catalysts is the N-acyl-L-homoserine lactone (AHL) lactonases, which rely on a dinuclear metal ion active site to hydrolytically cleave the autoinducer's lactone bond and inactivate signaling. A detailed understanding of how this enzyme works can help in the design of more selective and efficient reagents. To facilitate these studies, we describe a methodology to heterologously express, purify, and conduct in vitro characterization of several metalloforms of the AHL lactonase from Bacillus thuringiensis (AiiA). These procedures should be applicable to similar enzymes and will facilitate the production of more useful quorum-quenching reagents for biochemical studies and possible therapeutic applications.

[Essential expression and inducible synthesis polymorphism of chitinase in Bacillus thuringiensis]

Chitinases were produced by a lot of microorganisms. Chitinase gene expression in most of the chitinase producing bacteria was inducible by chitin. Low levels of chitinase were observed in the presence of glucose. To date, however, the regulation of such chitinase gene in Bacillus thuringiensis had not been well studied. In this paper, all 77 Bacillus thuringiensis strains were grown in the medium with or without chitin. We measured quantitatively the chitinase activity of the cultures. Moreover, we investigated the suppressive effect of glucose on chitinase of 4 strains. Also we studied the relationship between chitin induction and glucose suppression on chitinase. This investigation demonstrated that all tested B. thuringiensis strains could produce chitinase without chitin. After induction, the chitinolytic activity of 31 tested strains had no obvious response to the inducer, whereas 44 stains increased in different degree. Among these strains, most of them did not markedly increase the levels of chitinase, and many stains simultaneously displayed the expression mode of inducible and constitutive. The glucose inhibited the inductive effect of chitin, but it could not inhibit the basal expression of chitinase. Two strains No. 38 and No. 75 belonged to different expression types. But we just found several different bases in the regulatory region of chitinase genes chiA and chiB from them.

Metal displacement and stoichiometry of protein-metal complexes under native conditions using capillary electrophoresis/mass spectrometry

Increases in the study of protein-metal complexes, as well as in metal displacement in protein-metal complexes under native conditions for optimum catalytic properties in drug research and catalyst design, demands a separation/detection technology that can accurately measure metal displacement and stoichiometry in protein-metal complexes. Both nuclear magnetic resonance (NMR) and X-ray diffraction techniques have been used for this purpose; however, these techniques lack sensitivity. Electrospray ionization mass spectrometry (ESI-MS) using direct infusion offers higher sensitivity than the former techniques and provides molecular distribution of various protein-metal complexes. However, since protein-metal complexes under native conditions usually are dissolved in salt solutions, their direct ESI-MS analysis requires off-line sample clean-up prior to MS analysis to avoid sample suppression during ESI. Moreover, direct infusion of the salty solution promotes non-specific salt adduct formation by the protein-metal complexes under ESI-MS, which complicates the identification and stoichiometry measurements of the protein-metal complexes. Because of the high mass of protein-metal complexes and lack of sufficient resolution by most mass spectrometers to separate non-specific from specific metal-protein complexes, accurate protein-metal stoichiometry measurements require some form of sample clean up prior to ESI-MS analysis. In this study, we demonstrate that capillary electrophoresis/electrospray ionization in conjunction with a medium-resolution (approximately 10,000) mass spectrometer is an efficient and fast method for the measurement of the stoichiometry of the protein-metal complexes under physiological conditions (pH approximately 7). The metal displacement of Co(2+) to Cd(2+), two metal ions necessary for activation in the monomeric AHL lactonase produced by B. thuringiensis, has been used as a proof of concept.

[Heterogeneous expression of chitinase gene from Bcillus licheniformis MY75 and the characterization of expressed ChiMY]

OBJECTIVE

To heterogeneously express the chitinase gene of Bacillus licheniformis strain MY75 in E. coli, and to characterize the recombinant chitinase ChiMY.

METHODS

The extracelluar crude protein from B. licheniformis MY75 was analyzed by zymogram analysis. The partial amino acid sequence of the protein owned chitinase activity was given by time-of-flight mass spectrometry (TOF-MS). Then the corresponding chitinase gene chiMY was cloned and heterogeneously expressed in E. coli. The optimum temperature and pH of the ChiMY, and the effect of various metal ions on chitinase activity were studied. The antifungal activity and the synergistic effect on insecticidal activity were demonstrated by bioassays.

RESULTS

A 55 kDa extracelluar protein produced by B. licheniformis MY75 exhibited chitinase activity in zymogram analysis. The chiMY gene was 1797 bp long and encoded a 599 amino acid protein. The molecular weight of the recombinant protein ChiMY over-expressed in E. coli was 67 kDa. The amino acid sequence of the 55 kDa extracelluar protein was proved identical to the 67 kDa ChiMY by the TOF-MS. The optimum temperature and pH were 50 degrees C and 7.0, respectively. The enzyme activity was improved by Li+, Na+ and Mg2+ and inhibited by Mn2+, Cr3+, Zn2+, and Ag+. Cu2+ and Fe3+ can inactivate the enzyme. The bioassays demonstrated the heterogeneously expressed ChiMY could inhibit the sporangia germination of G. saubinetii and A. niger, and reduce the LC50 (50% lethal concentration) of the crystal protein of Bacillus thuringiensis against S. exigua by approximately 27%.

CONCLUSIONS

The B. licheniformis MY75 could produce a 55 kDa chitinase. The corresponding chitinase gene was over-expressed in E. coli. The molecular weight of heterogeneously expressed ChiMY showed significant different to the wild-type chitinase protein. This implicated the the protein processing of chitinase in the B. licheniformis MY75. The ChiMY also owned the antifungal activity and could improve the insecticidal activity of the Bacillus thuringiensis crystal protein against S. exigua. This is the first report about the chitinase from B. licheniformis in China.

[Spectrophometric analysis of volatile compounds in microorganisms]

A simple modification of a spectrophometric method was proposed for the rapid detection of microorganisms based on their ability either to excrete or to absorb volatile compounds. The method provides the possibility of contactless control for bacterial growth at a concentration above 10(7) cells/ml. In addition, the method allows discriminating mutants of the fungus Neurospora crassa defective in the nitrogen metabolism from the wild type strains. It is likely that nitrite reductase and nitrate reductase enzymes regulated by the nit-2 and nit-6 genes are involved in formation of the water soluble volatile compounds of this organism.

Transgenic Amorphophallus konjac expressing synthesized acyl-homoserine lactonase (aiiA) gene exhibit enhanced resistance to soft rot disease

Amorphophallus konjac is an important economic crop widely used in health products and biomaterials. However, this monocotyledonous plant's production is seriously restricted by soft rot disease. Some Bacillus thuringiensis strains generate an endocellular acyl homoserine lactonase (AiiA), which has inhibitory effect on soft rot pathogen through disrupting the signal molecules (N-acylhomoserine lactones, AHL) of their Quorum Sensing system. The aim of our study is to obtain transgenic A. konjac expressing AiiA protein and exhibiting resistance to soft rot. But till now, there is not any report about exogenous gene transformation in A. konjac. In this research, an Agrobacterium-mediated genetic transformation system was constructed. An aiiA gene was synthesized according to the codon usage in A. konjac. Embryogenic callus was infected with the A. tumefaciens strain EHA105 harboring the plant transformation plasmid pU1301 plus synthesized aiiA gene. After antibiotics screening, 34 plants were obtained. PCR analysis showed that positive amplified fragments were present in 21 out of these 34 lines. Southern blot analysis indicated that aiiA gene had integrated into the genome of A. konjac. Western blotting demonstrated that the target protein of interest was reactive with the antibody against AiiA. Further disease resistance detection revealed that all of the tested transgenic A. konjac lines exhibited high resistance to soft rot bacteria Erwinia carotovora subsp. Carotovora (Ecc) SCG1. The protocol is useful for the quality improvement of A. konjac through genetic transformation.

Binding affinity and larvicidal activity of a novel vegetative insecticidal protein Vip3V

Bacillus thuringiensis (Bt) is a well-known entomo-pathogen. Strains of Bt. that are toxic to a variety of insects belonging to various orders such as Lepidoptera, Diptera and Coleoptra have been identified, their larvicidal proteins isolated, characterized and used extensively in agriculture for protecting the economically important crops against these pests. Recently a novel group of vegetative insecticidal genes, vip3S and vip3V coding for 789-amino acid (88.5 kDa) protein in Bacillus thuringiensis was cloned and expressed in Escherichia coli and found to be highly sensitive to most of the agricultural pests and even towards the resistant insects. The binding affinity of these toxins to the receptors of these insect pests and relation between the affinity and larvicidal activity were carried out. Labeling of the toxin proteins with radioactive 125I and preparation of the Brush border membrane vesicles of the receptors were carried out. Analysis of saturation kinetics (Kd) and binding constants (Bmax) by competition assays revealed direct correlation between the binding affinity of the toxin to the receptor and insect mortality.

A novel l-isoleucine hydroxylating enzyme, l-isoleucine dioxygenase from Bacillus thuringiensis, produces (2S,3R,4S)-4-hydroxyisoleucine

The unique function of 4-hydroxyisoleucine (4-HIL) is to stimulate glucose-induced insulin secretion in a glucose-dependent manner. 4-HIL is distributed only in certain kinds of plants and mushrooms, but the biosynthetic mechanism of 4-HIL has not been elucidated. Moreover, 4-HIL-producing microorganisms have not been reported. l-isoleucine (l-Ile) hydroxylating activity producing 4-HIL was detected in a cell lysate of Bacillus thuringiensis strain 2e2 AKU 0251 obtained from the mid-late exponential phase of growth. Properties of the purified hydroxylase demonstrated that it is a alpha-ketoglutaric acid (alpha-KG) dependent l-Ile dioxygenase (IDO) and requires alpha-KG, ferric ion, and ascorbic acid for its maximum activity. IDO showed high stereoselectivity in l-Ile hydroxylation producing only (2S,3R,4S)-4-HIL. The N-terminal 22 amino acids sequence revealed high homology to a hypothetical protein (GenBank ID: RBTH_06809) in B. thuringiensis serovar israelensis ATCC 35646. The histidine motif, which is conserved in alpha-KG dependent dioxygenases, is found in RBTH_06809.

Entomotoxicity, protease and chitinase activity of Bacillus thuringiensis fermented wastewater sludge with a high solids content

This study investigated the production of biopesticides, protease and chitinase activity by Bacillus thuringiensis grown in raw wastewater sludge at high solids concentration (30 g/L). The rheology of wastewater sludge was modified with addition of Tween-80 (0.2% v/v). This addition resulted in 1.6 and 1.3-fold increase in cell and spore count, respectively. The maximum specific growth rate (micro(max)) augmented from 0.17 to 0.22 h(-1) and entomotoxicity (Tx) increased by 29.7%. Meanwhile, volumetric mass transfer coefficient (k(L)a) showed marked variations during fermentation, and oxygen uptake rate (OUR) increased 2-fold. The proteolytic activity increased while chitinase decreased for Tween amended wastewater sludge, but the entomotoxicity increased. The specific entomotoxicity followed power law when plotted against spore concentration and the relation between Tx and protease activity was linear. The viscosity varied and volume percent of particles increased in Tween-80 amended wastewater sludge and particle size (D(50)) decreased at the end of fermentation. Thus, there was an increase in entomotoxicity at higher suspended solids (30 g/L) as Tween addition improved rheology (viscosity, particle size, surface tension); enhanced maximum growth rate and OUR.

[Chitinase B from Bacillus thuringiensis enhancing potential and its antagonism and insecticidal]

OBJECTIVE

We studied the characteristics of chitinase B (ChiB) from Bacillus thuringiensis subsp. colmeri 15A3 (Bt 15A3) and evaluated its antagonism and insecticidal potential.

METHODS

ChiB was expressed in Escherichia coli. Expression product was purified by ammonium sulfate precipitation, dialysis and Sephadex G-200 gel filtration chromatography. The molecular mass of ChiB was directly estimated by zymogram after sodium dodecyl sulfate-polyacryamide gel electroresis (SDS-PAGE). The proteins with different molecular weight were identified by mass spectrum (MS) and analyzed through bioinformatics. We studied some metal ions' impacts on chitinase activity; optimal temperature, pH and its stability at different temperature and pH. We also studied the inhibition effects on sporangia germination of fungi and the synergistic effects of ChiB on larvicidal activity.

RESULTS

The molecular mass of ChiB was estimated as 70 kDa by zymogram. The protein with 64 kDa was the product of C-terminal degradation of ChiB in E. coli. Chitinase activity was improved by Fe3+ and inhibited by Zn2+ and Ag2+. The optimal temperature for ChiB was 60 C and the optimal pH was 5.0. The enzyme was quite stable at temperature below 60 degrees C and pH between 4.0 and 8.0. ChiB inhibited sporangia germination and the IC50 (50% inhibited concentration) was about 4 microg/mL. Moreover, the bioassays showed that ChiB could reduce the LC50 (50% lethal concentration) of the crystal protein of Bt. against Spodoptera exigua and Helicoverpa armigera larvae by approximately 26% and 30%.

CONCLUSION

ChiB was not only stable, but also with good antagonism and insecticidal activity.

The role of AiiA, a quorum-quenching enzyme from Bacillus thuringiensis, on the rhizosphere competence

Bacteria sense their population density and coordinate the expression of target genes, including virulence factors in Gram-negative bacteria, by the N-acylhomoserine lactones (AHLs)-dependent quorum-sensing (QS) mechanism. In contrast, several soil bacteria are able to interfere with QS by enzymatic degradation of AHLs, referred to as quorum quenching. A potent AHL-degrading enzyme, AiiA, of Bacillus thuringiensis has been reported to effectively attenuate the virulence of bacteria by quorum quenching. However, little is known about the role of AiiA in B. thuringiensis itself. In the present study, an aiiA-defective mutant was generated to investigate the role of AiiA in rhizosphere competence in the root system of pepper. The aiiA mutant showed no detectable AHL-degrading activity and was less effective for suppression of soft-rot symptom caused by Erwinia carotovora on the potato slice. On the pepper root, the survival rate of the aiiA mutant significantly decreased over time compared with that of wild type. Interestingly, viable cell count analysis revealed that the bacterial number and composition of E. carotovora were not different between treatments of wild type and the aiiA mutant, although root application of the aiiA mutant in pepper failed to protect the plant from root rot. These results provide evidence that AiiA can play an important role in rhizosphere competentce of B. thuringiensis and bacterial quorum quenching to Gram-negative bacteria without changing bacterial number or composition.

[Prediction, overexpression and activity confirmation of adenylation domain in Zwittermicin A biosynthesis gene cluster]

OBJECTIVE

The adenylation domain is required for the substrate activation of non-ribosomal peptide synthesis. The objective of this research was to prove that 2, 3-diaminopropionate is one of the presume precursors of Zwittermicin A biosynthesis.

METHODS

We cloned the adenylation domain in the Zwittermicin A synthesis cluster of Bacillus thuringiensis strain YBT-1520 with PCR amplification. After a series of enzyme digestions and subclonings, new expression vectors pBMB1312 was obtained. In order to detect the proper condition for overexpression, we tried different Isopropyl beta-D-1-thiogalactopyranoside (IPTG) concentration and temperature during overepression.

RESULTS

The overexpression protein of this domain could be purified under 20 degrees C, 0.1 mmol/L Isopropyl beta-D-1-thiogalactopyranoside (IPTG), BL21 codon plus RP (DE3) as the host strain. Then, PPi release assay indicated that 2, 3-diaminopropionate, the presume precursor of Zwittermicin A, could be adenylated by the adenylation domain.

CONCLUSION

This research confirmed that 2, 3-diaminopropionate is one of the presume precursors of Zwittermicin A biosynthesis.

Mechanism of the quorum-quenching lactonase (AiiA) from Bacillus thuringiensis. 1. Product-bound structures

Enzymes capable of hydrolyzing N-acyl- l-homoserine lactones (AHLs) used in some bacterial quorum-sensing pathways are of considerable interest for their ability to block undesirable phenotypes. Most known AHL hydrolases that catalyze ring opening (AHL lactonases) are members of the metallo-beta-lactamase enzyme superfamily and rely on a dinuclear zinc site for catalysis and stability. Here we report the three-dimensional structures of three product complexes formed with the AHL lactonase from Bacillus thuringiensis. Structures of the lactonase bound with two different concentrations of the ring-opened product of N-hexanoyl- l-homoserine lactone are determined at 0.95 and 1.4 A resolution and exhibit different product configurations. A structure of the ring-opened product of the non-natural N-hexanoyl- l-homocysteine thiolactone at 1.3 A resolution is also determined. On the basis of these product-bound structures, a substrate-binding model is presented that differs from previous proposals. Additionally, the proximity of the product to active-site residues and observed changes in protein conformation and metal coordination provide insight into the catalytic mechanism of this quorum-quenching metalloenzyme.

Improving the insecticidal activity by expression of a recombinant cry1Ac gene with chitinase-encoding gene in acrystalliferous Bacillus thuringiensis

In order to improve the insecticidal activity, the chitinase gene from tobacco (Nicotiana tabacum) endochitinase and the cry1Ac gene from Bacillus thuringiensis were cloned into the vector pHT315 and designated as pHUAccB5 plasmid. The constructed transcriptional fusion was attempted under the control of the native cry1Ac promoter. Plasmid pHUAccB5 was introduced into B. thuringiensis acrystalliferous by electroporation. Analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot, the transformant XBU-HUAccB5 produced 130-kDa Cry1Ac protein and 30-kDa chitinase protein. During the chitinase active analysis, the transformant, XBU-HUAccB5 chitinase active, reached 7.5 U/mL at 72 h, and was 5 times higher than the HTX-42 and 6 times higher than the parent strains. When the insecticidal activity of the transformant was evaluated against Helicoverpa armigera Hubner, the XBU-HUAccB5 toxicity was 11.30 times higher than the transformant HTX-42 expressed single cry1Ac at 48 h and was 18.76 times higher at 72 h.

A nonribosomal peptide synthetase gene tzw1 is involved in zwittermicin A biosynthesis in Bacillus thuringiensis G03

A 4.20-kb SspI fragment from Bacillus thuringiensis G03 was cloned and sequenced. Sequencing analysis revealed two complete open reading frames (ORF; tzw1 and tzw2), and one incomplete ORF (tzw3) (GenBank accession no. EU293887). Tzw1 encodes a putative nonribosomal peptide synthetase with thiolation and condensation domains localized at the C-termini, whereas tzw2 and tzw3 encode acyl carrier protein and Acyl-CoA dehydrogenase, respectively. To investigate the function of tzw1 in zwittermicin A (ZA) biosynthesis, an in-frame deletion of 1,461 bp within tzw1 was constructed. The mutant abolished ZA production. Complementation of the mutant with cloned tzw1 restored ZA productivity. These results revealed that tzw1 is required for ZA biosynthesis in B. thuringiensis G03.

Identification and expression of GH-8 family chitosanases from several Bacillus thuringiensis subspecies

The Gram-positive spore-forming bacterium, Bacillus thuringiensis, a member of the Bacillus cereus group, produces chitosanases that catalyze the hydrolysis of chitosan to chitosan-oligosaccharides (COS). Although fungal and bacterial chitosanases belonging to other glycoside hydrolase (GH) families have been characterized in a variety of microorganisms, knowledge on the genetics and phylogeny of the GH-8 chitosanases remains limited. Nine genes encoding chitosanases were cloned from 29 different serovar strains of B. thuringiensis and they were expressed in Escherichia coli. The ORFs of the chitosanases contained 1,359 nucleotides and the protein products had high levels of sequence identity (>96%) to other Bacillus species GH-8 chitosanases. Thin-layer chromatography and HPLC analyses demonstrated that these enzymes hydrolyzed chitosan to a chitosan-trimer and a chitosan-tetramer as major products, and this could be useful in the production of COS. In addition, a simple plate assay was developed, involving a soluble chitosan, for high-throughput screening of chitosanases. This system allowed screening for mutant enzymes with higher enzyme activity generated by error-prone PCR, indicating that it can be used for directed chitosanase evolution.

Purification and identification of a novel leucine aminopeptidase from Bacillus thuringiensis israelensis

A novel leucine aminopeptidase was purified from a Bacillus thuringiensis israelensis (Bti) culture. The purification stages included heating the concentrated supernatant to 65 degrees C for 90 min, anion-exchange chromatography by DEAE cellulose, and hydrophobic chromatography by phenyl Sepharose. The specific activity of leucine aminopeptidase after the hydrophobic chromatography increased by 215.5-fold and the yield was 16%. The molecular weight of the active enzyme was 59 kDa. Mass spectrometry analysis of the 59-kDa leucine aminopeptidase revealed that this protein has at least 41% homology with the cytosol leucine aminopeptidase produced by Bacillus cereus. Maximal leucine aminopeptidase activity occurred at 65 degrees C, pH 10 toward leucine as the amino acid terminus. The enzyme was strongly inhibited by bestatin, dithiothreitol, and 1,10-phenanthroline, indicating that the enzyme might be considered as a metallo-aminopeptidase that has disulfide bonds at the catalytic site or at a region that influences its configuration. Examination of the purified leucine aminopeptidase's effect on the activation of the protoxin Cyt1Aa from Bti revealed that when it acts synergistically with Bti endogenous proteases, it has only a minor role in the processing of Cyt1Aa into an active toxin.

Effect of the chitin binding domain deletion from Bacillus thuringiensis subsp. kurstaki chitinase Chi255 on its stability in Escherichia coli

Bacillus thuringiensis subsp. kurstaki BUPM255 secretes a chitobiosidase Chi255 having an expected molecular weight of 70.665 kDa. When the corresponding gene, chi255, was expressed in E. coli, the active form, extracted from the periplasmic fraction of E. coli/pBADchi255, was of about 54 kDa, which suggested that Chi255 was excessively degraded by the action of E. coli proteases. Therefore, in vitro progressive C-terminal Chi255 deleted derivatives were constructed in order to study their stability and their activity in E. coli. Interestingly, when the chitin binding domain (CBD) was deleted from Chi255, an active form (Chi2555Delta5) of expected size of about 60 kDa was extracted from the E. coli periplasmic fraction, without the observation of any proteolytic degradation. Compared to Chi255, Chi255Delta5 exhibited a higher chitinase activity on colloidal chitin. Both of the enzymes exhibit activities at broad pH and temperature ranges with maximal enzyme activities at pH 5 and pH 6 and at temperatures 50 degrees C and 40 degrees C, respectively for Chi255 and Chi255Delta5. Thus, it was concluded that the C-terminal deletion of Chi255 CBD might be a nice tool for avoiding the excessive chitinase degradation, observed in the native chitinase, and for improving its activity.

Cloning and identification of a gene encoding spore cortex-lytic enzyme in Bacillus thuringiensis

Spore cortex-lytic enzymes are essential for germination in Bacilli. A gene-encoding spore cortex-lytic enzyme designated sleB was cloned from Bacillus thuringiensis. Disruption of sleB did not affect vegetative growth of B. thuringiensis, but the fall in optical density at 600 nm in the mutant spores was much slower than in the wild type strain during spore germination induced by L-alanine. Moreover, the mutant spores did not become completely dark, as compared with the wild type strain. These showed that sleB is required for normal spore germination in B. thuringiensis. Reverse transcription polymerase chain reaction analysis indicated that sleB is transcribed during sporulation. Western blot experiment also proved that SleB accumulated in sporulating cells as a precursor protein, and in spores as a mature processed form.

Interference of quorum sensing and virulence of the rice pathogen Burkholderia glumae by an engineered endophytic bacterium

Many bacterial species are known to thrive within plants. Among these bacteria, a group referred to as endophytes provide beneficial effects to the host plants by the promotion of plant growth and the suppression of plant pathogens. Among 44 putative endophytic isolates isolated from surface-sterilized rice roots, Burkholderia sp. KJ006 was selected for further study because of a lack of pathogenicity to rice, a broad spectrum of antifungal properties, and the presence of the nifH gene, which is an indicator for nitrogen fixation. In an attempt to control Burkholderia glumae, a casual pathogen of seedling rot and grain rot of rice, an N-acyl-homoserine lactonase (aiiA) gene from Bacillus thuringiensis was introduced into Burkholderia sp. KJ006 given that the major virulence factor of Burkholderia glumae is controlled in a population-dependent manner (quorum sensing). The engineered strain KJ006 (pKPE-aiiA) inhibited production of quorum-sensing signals by Burkholderia glumae in vitro and reduced the disease incidence of rice seedling rot caused by Burkholderia glumae in situ. Our results indicate the possibility that a bacterial endophyte transformed with the aiiA gene can be used as a novel biological control agent against pathogenic Burkholderia glumae that are known to occupy the same ecological niche.

Identification and characterization of a polysaccharide deacetylase gene from Bacillus thuringiensis

One polysaccharide deacetylase gene was cloned from Bacillus thuringiensis and designated pdaA. Disruption of pdaA did not affect vegetative growth and sporulation but obviously affected spore germination. When L-alanine was added into the spore suspension, the spores of the pdaA disruption mutant showed a slow and partial reduction in absorbance at OD600 and became phase pale gray compared with phase dark of the wild-type strain. In contrast with the outgrowing of wild-type spores after germination, the pdaA mutant spores were blocked at the stage of spore germination. Transmission electron micrographs revealed a significant difference between the pdaA mutant and the wild-type strain in the spore cortex. Introduction of the pdaA gene into the pdaA disruption mutant complemented the germination-negative phenotype. Reverse transcription--polymerase chain reaction showed that pdaA was transcribed after incubation for 10 h in CCY medium.

A fundamental dual regulatory role of citrate on the biosyntheses of thuringiensin and poly-β-hydroxybutyrate in Bacillus thuringiensis YBT-032

The production of alpha-ketoglutarate, adenine, thuringiensin production rate and thuringiensin yield on glucose consumed increased by 22%, 36%, 40% and 40%, respectively, in presence of 2 g citrate/l. However, citrate decreased pyruvate production, poly-beta-hydroxybutyrate (PHB) production rate and PHB yield by 62%, 31% and 45%, respectively. The activities of pyruvate kinase and glucose-6-phosphate dehydrogenase were 36%-45% lower and 50%-120% higher than those of the control, respectively. The results suggest that citrate regulated the carbon flux to synthesis of adenine present in thuringiensin with a higher efficiency of utilization of glucose by decreasing PHB synthesis.

Differentiation between Bacillus thuringiensis strains by gyrB PCR-Sau3Al fingerprinting

gyrB DNA fragments of seven Bacillus thuringiensis local collection family representatives were amplified by PCR and sequenced. Several differences in their corresponding sequences were evidenced. Both in silico and in vitro restriction maps of gyrB sequences and fragments respectively confirmed that EcoRI and Sau3AI could be used to differentiate between B. thuringiensis strains. However, the phylogeny analysis showed that only the gyrB PCR-Sau3AI allows a strains classification that correlates very well with that obtained on the basis of the sequences analysis. Thus, these finds show that gyrB PCR- Sau3AI digestion could be considered as an efficient, rapid, and easy method to make a distinction, not only between strains belonging to the Bacillus cereus group, but also between those belonging to B. thuringiensis.

Fusion of the genes for AHL-lactonase and S-layer protein in Bacillus thuringiensis increases its ability to inhibit soft rot caused by Erwinia carotovora

Two genes, ctc and ctc2, responsible for surface layer (S-layer) protein synthesis in Bacillus thuringiensis CTC, were mutated and resulted in B. thuringiensis Tr5. To synthesize and express the N-acyl-homoserine lactonase (AHL-lactonase) in the extracellular space of B. thuringiensis, the aiiA ( 4Q7 ) gene (an AHL-lactonase gene from B. thuringiensis 4Q7), which confers the ability to inhibit plant soft rot disease in B. thuringiensis 4Q7, was fused with the upstream sequence of the ctc gene, which in turn is essential for S-layer protein secretion and anchoring on the cell surface. The resulting fusion gene, slh-aiiA, was expressed in B. thuringiensis Tr5 to avoid competition for the extracellular space with the native S-layer protein. Our results indicate that B. thuringiensis Tr5 containing the fusion gene slh-aiiA displayed high extracellular AHL-degrading activity. When compared with wild-type B. thuringiensis strains, the ability of the constructed strain to inhibit soft rot disease caused by Erwinia carotovora SCG1 was markedly increased. These findings provide evidence for a significant advance in our ability to inhibit soft rot disease caused by E. carotovora.