Restraining Erwinia virulence by expression of N-acyl homoserine lactonase gene pro3A-aiiA in Bacillus thuringiensis subsp leesis

Quorum sensing inhibitors as antipathogens: biotechnological applications

The mechanisms through which microbes communicate using signal molecules has inspired a great deal of research. Microbes use this exchange of information, known as quorum sensing (QS), to initiate and perpetuate infectious diseases in eukaryotic organisms, evading the eukaryotic defense system by multiplying and expressing their pathogenicity through QS regulation. The major issue to arise from such networks is increased bacterial resistance to antibiotics, resulting from QS-dependent mediation of the formation of biofilm, the induction of efflux pumps, and the production of antibiotics. QS inhibitors (QSIs) of diverse origins have been shown to act as potential antipathogens. In this review, we focus on the use of QSIs to counter diseases in humans as well as plants and animals of economic importance. We also discuss the challenges encountered in the potential applications of QSIs.

Evidence-based validation of quorum quenching from Lysinibacillus sphaericus and Geobacillus sp. in bioremediation of oil sludge

Many studies on quorum quenching focus on the discovery and characterization of novel acyl-homoserine lactonases (AHL-lactonases) because these enzymes could be used in the control of diseases caused by Gram-negative bacteria. The effects of quorum quenching are also remarkable in the performance of bacterial consortia in applications such as bioremediation. In the current work, we demonstrated the presence of a potential novel AHL-lactonase-encoding locus (Bsph_3377) from Lysinibacillus sphaericus and Geobacillus sp. The deduced amino acid sequences for this enzyme possess the characteristic domains and motifs involved in Zn-binding from AHL lactonases and were grouped into 1 clade within the phylogeny of the lactonases from firmicutes, showing 70% of identity with the lactonase AhlS from Solibacillus silvestris. We demonstrated the locus transcription by RT-qPCR and its relationship with the suppression of the pathogenicity of Pectobacterium carotovorum. Additionally, we analyzed the interaction of these bacilli with a commercial consortium in the bioremediation of a hydrocarbon-contaminated soil, showing inhibitory effects on its establishment. These results represent a new contribution in the understanding of the potential biotechnological applications of L. sphaericus and Geobacillus sp. as well as in the research on antibacterial techniques based on quorum-sensing disruption.

Exploiting quorum sensing to confuse bacterial pathogens

Cell-cell communication, or quorum sensing, is a widespread phenomenon in bacteria that is used to coordinate gene expression among local populations. Its use by bacterial pathogens to regulate genes that promote invasion, defense, and spread has been particularly well documented. With the ongoing emergence of antibiotic-resistant pathogens, there is a current need for development of alternative therapeutic strategies. An antivirulence approach by which quorum sensing is impeded has caught on as a viable means to manipulate bacterial processes, especially pathogenic traits that are harmful to human and animal health and agricultural productivity. The identification and development of chemical compounds and enzymes that facilitate quorum-sensing inhibition (QSI) by targeting signaling molecules, signal biogenesis, or signal detection are reviewed here. Overall, the evidence suggests that QSI therapy may be efficacious against some, but not necessarily all, bacterial pathogens, and several failures and ongoing concerns that may steer future studies in productive directions are discussed. Nevertheless, various QSI successes have rightfully perpetuated excitement surrounding new potential therapies, and this review highlights promising QSI leads in disrupting pathogenesis in both plants and animals.

A novel metagenomic short-chain dehydrogenase/reductase attenuates Pseudomonas aeruginosa biofilm formation and virulence on Caenorhabditis elegans

In Pseudomonas aeruginosa, the expression of a number of virulence factors, as well as biofilm formation, are controlled by quorum sensing (QS). N-Acylhomoserine lactones (AHLs) are an important class of signaling molecules involved in bacterial QS and in many pathogenic bacteria infection and host colonization are AHL-dependent. The AHL signaling molecules are subject to inactivation mainly by hydrolases (Enzyme Commission class number EC 3) (i.e. N-acyl-homoserine lactonases and N-acyl-homoserine-lactone acylases). Only little is known on quorum quenching mechanisms of oxidoreductases (EC 1). Here we report on the identification and structural characterization of the first NADP-dependent short-chain dehydrogenase/reductase (SDR) involved in inactivation of N-(3-oxo-dodecanoyl)-L-homoserine lactone (3-oxo-C(12)-HSL) and derived from a metagenome library. The corresponding gene was isolated from a soil metagenome and designated bpiB09. Heterologous expression and crystallographic studies established BpiB09 as an NADP-dependent reductase. Although AHLs are probably not the native substrate of this metagenome-derived enzyme, its expression in P. aeruginosa PAO1 resulted in significantly reduced pyocyanin production, decreased motility, poor biofilm formation and absent paralysis of Caenorhabditis elegans. Furthermore, a genome-wide transcriptome study suggested that the level of lasI and rhlI transcription together with 36 well known QS regulated genes was significantly (≥10-fold) affected in P. aeruginosa strains expressing the bpiB09 gene in pBBR1MCS-5. Thus AHL oxidoreductases could be considered as potent tools for the development of quorum quenching strategies.

Modulation of a thermoregulated type VI secretion system by AHL-dependent quorum sensing in Yersinia pseudotuberculosis

The type VI secretion system (T6SS) is a novel secretion system found in many Gram-negative bacterial pathogens, which appears to be tightly regulated by different regulatory mechanisms. In the present study, we identified 4 T6SS clusters in Yersinia pseudotuberculosis and demonstrated that they were differentially thermoregulated. Among them, T6SS4 was preferentially expressed at 26°C, and its expression was growth phase dependent and subject to quorum sensing regulation. Both YpsI and YtbI AHL synthases contributed to the positive regulation of T6SS4, whereas YpsI synthase played the major role as T6SS4 expression was reduced strongly in the ypsI mutant strain but weakly in the ytbI mutant strain. Moreover, we provided evidence that exogenous addition of different synthetic AHLs complemented T6SS4 expression in different efficiencies in an ypsIytbI double mutant strain, suggesting C6-HSL had an antagonistic effect on T6SS4 expression. This is the first study demonstrating that the expression of T6SS is precisely regulated by temperature, growth phase, and AHL-dependent quorum sensing systems in Y. pseudotuberculosis.

The acylase PvdQ has a conserved function among fluorescent Pseudomonas spp

Pyoverdine biosynthesis in fluorescent Pseudomonas spp. and especially in the opportunistic human pathogen Pseudomonas aeruginosa has been extensively studied. The acylase PvdQ is required for a maturation step in pyoverdine biosynthesis but also has been proven to be effective in degrading long-chain N-acyl homoserine lactones (AHLs). These molecules are used as quorum-sensing molecules by Gram-negative bacteria such as Pseudomonads themselves. Interestingly, the pvdQ gene is part of a pyoverdine cluster in P. aeruginosa and P. syringae but not in other fluorescent Pseudomonas spp. In this study we have compared the activities of PvdQ orthologues from various species and provide evidence for conserved functions in Pseudomonas fluorescens PfO-1, P. putida KT2440 and P. aeruginosa PA14. Despite large differences in genomic organization, expression of each of these pvdQ orthologues is regulated by iron availability. Moreover, PvdQ and its orthologues have conserved substrate specificity for AHLs and play a role in pyoverdine production in all tested Pseudomonas species. These data strongly suggest that the role of PvdQ in pyoverdine biosynthesis is conserved among Pseudomonas spp., while the control that PvdQ exerts in P. aeruginosa over its own quorum-sensing signals seems to be unique to this bacterium.

Enhancing Cry1Ac toxicity by expression of the Helicoverpa armigera cadherin fragment in Bacillus thuringiensis

Insect cadherin proteins localized in the midgut epithelium were identified as receptors for Bacillus thuringiensis insecticidal crystal proteins (Cry toxins). These cadherins facilitated toxin monomer oligomerization and mediated oligomer binding to secondary receptors. It has been reported that Manduca sexta, Helicoverpa armigera, Anopheles gambiae and Diabrotica virgifera cadherin toxin binding regions function as synergists for Cry1A, Cry4Ba and Cry3A toxicity against target insects. In the present study, the toxin binding region fragment of the H. armigera cadherin (hacad1) gene was cloned and fused with the promoter of the cry3Aa gene. The fusion gene pro3Aa-hacad1 and the cry1Ac gene were inserted into shuttle vector pHT304 and introduced into B. thuringiensis acrystalliferous strain BMB171 for coexpression (resulting in recombinant strain BMB1073). SDS-PAGE and mass spectrum analysis showed that BMB1073 could express HaCad1 and Cry1Ac proteins together. Bioassay results demonstrated that insecticidal activities against H. armigera and Spodoptera exigua could be increased 5.1-fold and 6.5-fold, respectively, by BMB1073 compared with the strain which can only express the Cry1Ac protein. Our discovery showed that coexpression of HaCad1 and Cry1Ac toxin in B. thuringiensis enhanced the insecticidal activity of Cry1Ac toward Lepidoptera insects. This finding also revealed a novel strategy for engineering strains and transgenic plants with higher insecticidal activity.

Helicoverpa armigera cadherin fragment enhances Cry1Ac insecticidal activity by facilitating toxin-oligomer formation

The interaction between Bacillus thuringiensis insecticidal crystal protein Cry1A and cadherin receptors in lepidopteran insects induces toxin oligomerization, which is essential for membrane insertion and mediates Cry1A toxicity. It has been reported that Manduca sexta cadherin fragment CR12-MPED and Anopheles gambiae cadherin fragment CR11-MPED enhance the insecticidal activity of Cry1Ab and Cry4Ba to certain lepidopteran and dipteran larvae species, respectively. This study reports that a Helicoverpa armigera cadherin fragment (HaCad1) containing its toxin binding region, expressed in Escherichia coli, enhanced Cry1Ac activity against H. armigera larvae. A binding assay showed that HaCad1 was able to bind to Cry1Ac in vitro and that this event did not block toxin binding to the brush border membrane microvilli prepared from H. armigera. When the residues (1423)GVLSLNFQ(1430) were deleted from the fragment, the subsequent mutation peptide lost its ability to bind Cry1Ac and the toxicity enhancement was also significantly reduced. Oligomerization tests showed that HaCad1 facilitates the formation of a 250-kDa oligomer of Cry1Ac-activated toxin in the midgut fluid environment. Oligomer formation was dependent upon the toxin binding to HaCad1, which was also necessary for the HaCad1-mediated enhancement effect. Our discovery reveals a novel strategy to enhance insecticidal activity or to overcome the resistance of insects to B. thuringiensis toxin-based biopesticides and transgenic crops.

Elaboration of an electroporation protocol for large plasmids and wild-type strains of Bacillus thuringiensis

AIMS

To elaborate an effective electroporation protocol for large plasmids and wild type strains of Bacillus thuringiensis.

METHODS AND RESULTS

The effect of DNA desalting, wall-weakening agency, cell growth conditions, electroporation solutions, and electric fields on electroporation efficiency was evaluated to optimize electroporation conditions for B. thuringiensis. By using this improved method, the greatest efficiency was reached 2 x 10(10 )CFU microg(-1) with pHT304, which is 10(4) times higher than previously reported. Four large plasmids (29.1, 44.9, 58 and 60 kb) were successfully transferred into the acrystalliferous B. thuringiensis strain BMB171; these results have not been achieved with previous protocols. Three wild type B. thuringiensis strains which could not be transformed previously were also transferred successfully.

CONCLUSIONS

This improved method is more efficient for small plasmids; it is also appropriate for large plasmids and wild type B. thuringiensis strains which were not transformed by previous procedures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study established an effective electroporation protocol for large plasmids and wild type strains of B. thuringiensis. This method is well suited for the cloning and expression of huge DNA fragments such as gene clusters in B. thuringiensis. It also can be used as a reference method for other Bacillus strains that are refractory to electroporate.

N-Acyl homoserine lactonase promotes prevention of Erwinia virulence with zwittermicin A-producing strain Bacillus cereus

Zwittermicin A (ZwA), a hybrid polyketide- peptide antibiotic, and N-acyl -homoserine-lactonase (AHL-lactonase), a kind of quorum-quenching enzyme, have the potential to prevent the virulence of Erwinia carotovora, which is a major pathogen of soft rot. The purpose of this study was to combine the two agents in one host to improve their prevention efficacy. AHL-lactonase was over-expressed in the ZwA-producing strain Bacillus cereus and derivates were identified to create genetically modified (GM) strains. The comparative results showed that neither ZwA nor AHL-lactonase impacted the yield of the other; the increased yield of ZwA could promote the prevention efficacy of GM strains; Coexistence of ZwA and AHL-lactonase in the GM strains had better prevention efficacy than either has separately. It is a potential therapy to provide more effective prevention and withstand gradually increasing pesticide-resistance by combining the two antibacterial agents.