Computational prediction of active sites and ligands in different AHL quorum quenching lactonases and acylases

Rice tungro is a serious viral disease of rice resulting from infection by two viruses, Rice tungro bacilliformvirus and Rice tungro spherical virus. To gain molecular insights into the global gene expression changes inrice during tungro, a comparative whole genome transcriptome study was performed on healthy and tungroaffected rice plants using Illumina Hiseq 2500. About 10 GB of sequenced data comprising about 50 millionpaired end reads per sample were then aligned on to the rice genome. Gene expression analysis revealedaround 959 transcripts, related to various cellular pathways concerning stress response and hormonal homeostasis to be differentially expressed. The data was validated through qRT-PCR. Gene ontology and pathwayanalyses revealed enrichment of transcripts and processes similar to the differentially expressed genes categories. In short, the present study is a comprehensive coverage of the differential gene expression landscapeand provides molecular insights into the infection dynamics of the rice-tungro virus system

AidE encodes an N-acyl homoserine lactonase in Acinetobacter / 生物工程学报

Quorum sensing (QS) is a cell-cell communication mechanism that allows bacterial populations to coordinate gene expression in response to cell density. N-acylhomoserine lactones (AHL) are used as quorum-sensing signal molecules by many Gram negative bacteria. Acinetobacter sp. 77, an AHL-degrading bacterium, was isolated in our previous work. The gene aidE for AHL inactivation was cloned in this study by screening a genomic DNA library. The deduced protein AidE is 268 amino acids in length and shares a high identity (95%) with the beta-lactamase family protein in Acinetobacter gyllenbergii CIP110306, but low identities with known AHL-degrading enzymes. HPLC analysis of the AidE-degraded C6-HSL products revealed that AidE functioned as an AHL lactonase. Sequences alignment suggested that the aidE gene is not conserved in Acinetobacter species, flanking sequences of aidE and their arrangement are specific in Acinetobacter sp. 77 genome, and some IS insertion sequences were found downstream of the aidE gene. These evidences indicated that the aidE gene might be foreign DNA taken up via horizontal gene transferring or had changed its relative location due to the genome rear-arrangement. Expression of the aidE gene in Pectobacterium carotovorum subsp. carotovorum Z3-3 significantly reduced its AHL production as well as the pathogenicity on host plants, indicating that AidE was able to effectively quench quorum sensing-dependent functions in bacteria. In conclusion, aidE is a newfound AHL-lactonase with a potential for suppression of bacterial infections.

AHL-lactonase characteristics of Bacillus thuringiensis SGT3g and its effectiveness in inhibiting pathogenicity of Dickeya dadantii

ABSTRACT Aims: Dickeya dadantii is a pathogenic bacterium causing bacterial soft rot disease in plants. The bacterium uses a homoserine lactone signal in its quorum sensing process to express the virulence factor genes. Anti-quorum sensing is a new approach to control plant pathogenic bacteria. The aims of this study are to characterize AHL-lactonase enzyme produced by Bacillus thuringiensis SGT3g and to determine its effectiveness in inhibiting virulence of D. dadantii. Methodology and results: Activity of AHL-lactonase was determined using Chromobacterium violaceum as a bacterial biosensor. The crude extract enzymes of AHL-lactonase on both as extracellular and intracellular enzymes were analyzed their enzyme activity of protein precipitation and dialysis products. The optimum activity of AHL-lactonase was found at 30 °C and pH 5-8. Bacillus thuringiensis SGT3g was capable to reduce soft rot symptom disease caused by D. dadantii on Phalaenopsis orchid leaves after 24 h of incubation. Conclusion, significance and impact study: Bacillus thuringiensis SGT3g was capable to degrade AHL signal of C. violaceum and D. dadantii. The activity AHL-lactonase of B. thuringiensis SGT3g had a wide range of pH and temperature. The lactonase could reduce soft rot symptom disease caused by D. dadantii without any growth inhibition of D. dadantii on orchid leaves. Bacillus thuringiensis SGT3g can be used as an alternative biopesticide to control phytopathogenic bacteria due to its capability to suppress bacterial pathogenic virulence.

Screening & profiling of quorum sensing signal molecules in Pseudomonas aeruginosa isolates from catheterized urinary tract infection patients.

Background & objectives: Catheter associated urinary tract infections are the second most common nosocomial infections and Pseudomonas aeruginosa is the third most common organism responsible for these infections. In this study P. aeruginosa isolates from catheterized urinary tract infection patients were screened and profiled for the presence of different type of quorum sensing (QS) signal molecules. Methods: Screening and quantitation of AHLs was done by using cross feeding assay and by determining β-galactosidase activity respectively using Escherichia coli MG4 as reporter strain. Further, AHL profiles were determined by separating AHLs on TLC coupled with their detection using Chromobacterium violaceum CV026 and Agrobacterium tumifaciens A136 biosensor strains. Results: All uroisolates from catheterized patients having urinary tract infections were found to be producers of QS signal molecules. There were differences in amounts and type of AHL produced amongst uroisolates of P. aeruginosa. Several AHLs belonging to C4-HSL, C6-HSL, oxo-C6-HSL, C8-HSL, C10-HSL and C12-HSL were determined in these strains. Interpretation & conclusions: Simultaneous use of more than one reporter strain and assay method proved useful in determining the AHLs profile in uroisolates of P. aeruginosa. Observed differences in the amounts and types of AHLs may reflect differences in virulence potential of P. aeruginosa to cause UTIs which can be further confirmed by employing animal model system. The present study speculates that production of QS signal molecules may act as a new virulence marker of P. aeruginosa responsible for causing catheter associated UTIs and can be considered as futuristic potential drug targets towards treatment of UTIs.

Quorum sensing (QS) as etiological phenomenon: the bacterial paradigm.

Signaling mechanisms that govern physiological and morphological responses to change the cell density are common in bacteria. Quorum sensing is signal transduction processes which involves the production and release of and response to hormone-like molecules (auto-inducers) that accumulate in the external environment as the cell population grows. Quorum sensing is found in a wide variety of bacteria, both Gram-positive and Gram-negative and the spectrum of physiological functions that can be regulated is impressive. Variation in the nature of the extra-cellular signal in the signal detection machinery and in the mechanisms of signal transmission demonstrates the evolutionary adaptability of quorum sensing systems for multiple uses.

Study of the Correction between the Age Related Hearing Loss and the Cytoactivity Factors of the Cochlear Hair Cell in C57BL/6J Mice / 听力学及言语疾病杂志

Objective To establish the mice model of AHL, to investigate the relationship between AHL and the cytoactive factors of the cochlear hair cells in C57BL/6J mice, and to classify the presbycusis models of the C57BL/6J mice. Methods C57BL/6J mice were divided into 6 experimental groups by age (A: 3 months old(m), B: 8 m, C: 9 m, D: 10 m, F: 17 m, G: 18 m) . The auditory functions mice were measured by auditory brainstem response (ABR) with the stimulus click and toneburst at 6 kHz and 8 kHz. 3 months later, Groups C , G, E and H were tested again for ABR. After ABR testing, the cytoactive of the hair cells was detected by succinate dehydrogenase staining and surface preparation technique(two mice from each group except groups C and G). Results The ABR thresholds elevated with age, and the marked change of the cochlea was the degeneration of the cytoactive of the cochlear hair cells, especially those of the outer hair cells. In the beginning, the basement of the basal membrane suffered from the mitochondrion degeneration in the outer hair cells, then it spread to the top region. Subsequently, the inner hair cells were involved. Conclusion C57BL/6J mouse was a typical animal model for the AHL,and the main change of the cochlea was the degeneration of the hair cells, especially the outer hair cells. Thus, C57BL/6J mice can be used as a suitable animal model for the study of presbycusis.