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.
Systems Microbiology Research Center, KRIBB, Daejeon 305-806, Korea.
Su-Jin
SJ
Park
Sun-Yang
SY
Park
Choong-Min
CM
Ryu
Seung-Hwan
SH
Park
Jung-Kee
JK
Lee
D001413:Bacillus thuringiensis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002212:Capsicum / Q000382:microbiology*; D003001:Cloning, Molecular; D015169:Colony Count, Microbial; D008025:Ligases / Q000378:metabolism; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D016973:Pectobacterium carotovorum / Q000254:growth & development / Q000472:pathogenicity; D010935:Plant Diseases / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D053038:Quorum Sensing / Q000235:genetics
D001426:Bacterial Proteins; C406735:AiiA protein, Bacillus; D008666:Metalloendopeptidases; D008025:Ligases; C449816:N-acylhomoserine lactone synthase