Enhancing Effect Of AHL Lactonase On ZwA's Suppression Against Soft Rot Disease In Bacillus Cereus

Zwittermicin A(ZwA) is a broad spectrum, novel antibiotic produced by Bacillusthuringiensis and Bacillus cereus. ZwA shows diverse inhibitory activity against a broadtarget of plant pathogens, including highly activity against algal protists and a wide rangeof plant pathogenic fungi, and moderate activity against diverse Gram-negative bacteriaand certain Gram-postive bacteria.N-acyl-homoserine Lactones(AHLs), widely-spreaded signal molecules inQuorum-Sensing systems of many Gram-negative bacteria, can contribute to theinducement of the expression of many virulence genes. And Acyl-homoserineLactonase(AHL lactonase) can suppress certain plant diseases by degrading AHLs, whichcan shuttle in and out of cells.In order to increase disease suppression by combining the two different diseasesuppression mechanisms of ZwA and AHL lactonase, AHL lactonase gene was introducedinto ZwA~+ Bacillus cereus strains. In this study, two ways of enhacing the activity of AHLlactonase were adopted: on one hand, the expression of AHL gene(aiiA) was increased byconstructing a fusion gene pro3A-aiiA including aliA gene and a strong promoter ofinsecticidal crystal protein coding gene cry3Aa of Bacillus thuringiensis, and the fusiongene pro3A-aiiA was placed in pBMB686. On the other hand, in order to degrade AHLsout of the cells directly, AHL lactonase was displayed on the cell surface by constructinga fusion gene slh-aiiA including aiia gene and SLH motif of S-layer protein from Bacillusthruringiensis, and the fusion gene slh-aiiA was carried by pBMB3439. PlasmidspBMB686 and pBMB3439 were transformed into Bacillus cereus separately, and thedisease suppression of the two difference recombinants was compared.The results indicated that both pro3A-aiiA and slh-aiiA genes could be expressed inrecombinant strains, without affecting the expression level of ZwA. Furthermore, therecombinant stains exhibited stronger ability of AHLs inactivation and higher restraint tothe potato rot disease caused by Erwinia carotovora than their parental stains. Thus, it wasindicated it was feasible to increase disease suppression by combining the biologicalfunctions of ZwA and AHL lactonase.