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Title: ANALYSIS OF MUTANT DERIVATIVES OF BURKHOLDERIA AMBIFARIA AND B. MULTIMORANS ALTERED WITH RESPECT TO FORMATION OF N-ACYL HOMOSERINE LACTONES

Author
item YAO, F - UNIV MA, MICROBIOL.
item ZHOU, H - UNIV MA, MICROBIOL.
item Roberts, Daniel
item LESSIE, T - UNIV MA, MICROBIOL.

Submitted to: Proceedings of the International B. cepacia Working Group
Publication Type: Abstract Only
Publication Acceptance Date: 4/5/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: B. ambifaria BcF forms higher levels of AHL in vitro than most members of the B. cepacia complex, whereas B. multivorans forms essentially no AHLs, despite the fact that it possesses genes related to quorum sensing. We isolated mutant derivatives of B. multivorans, ATCC 17616 which produce high levels of AHL. We expected that they might have alterations in the the genes encoding AHL synthase (BmuI) and/or AHL-binding transcriptional activator (BmuR). As in the case of the cepI and cepR genes of the genomovar III isolate, strain K56-2, the bmuI and bmuR genes of B. multivorans 17616 were divergently oriented and separated by ca 700 nt. There was a lux box-like sequence and 70-like promoter immediately upstream of the bmuI gene. No promoter was detected in the region immediately upstream of the bmuR gene. There was a 396-nt open reading frame which terminated 134-nt upstream of bmuR. This ORF was preceded by a 70-like promoter. We speculate that this putative promoter might direct transcription of both the ORF and bmuR gene. Comparison of the bmuIR loci of AHL-overproducing derivatives of strain 17616 and their wild type parent failed to reveal differences in nucleotide sequence that might explain the increased formation of AHLs. Presumably the alterations in the mutant strains lie outside of the bmuIR locus in other genes governing quorum sensing. We speculate that these might be global regulatory genes whose activity depends upon whether or not the bacteria are host-associated. We also have isolated AHL-deficient mutants of the maize rhizosphere isolate B. ambifaria BcF which exhibit reduced antifungal activity against Saccharomyes cerevisiae, Pythium ultimum, Rhizoctonia solani, and Fusarium oxysporum f. sp. lycoperisici. In certain of the mutants genes related to quorum sensing were absent, suggesting that the bafIR locus is a hot spot for deletion. In both B. ambifaria and B. multivorans, which each contain three chromosomes, genes related to quorum sensing were located on the mid-size chromosome.