Representatives ofBacillusamyloliquefaciens were shown to possess biocontrol activity against fire blight,
a serious disease of orchard trees caused byErwinia amylovora. Genome analysis of B. amyloliquefaciens
FZB42 identified gene clusters responsible for synthesis of several polyketide compounds with antibacterial action. We show here that the antibacterial polyketides difficidin and to a minor extent bacillaene
act efficiently againstE. amylovora. Surprisingly, a mutant strain blocked in the production of difficidin
(CH8dfn) inhibited growth ofE. amylovoraand suppressed fire blight disease nearly in the same range
as the wild type. In addition, asfpmutant (CH3sfp) unable to synthesize non-ribosomally lipopeptides
and polyketides did still suppress growth ofE. amylovora,suggesting that besides action of polyketides
another antagonistic principle exist. A double mutant (RS06sfpbac) devoid in polyketide and bacilysin
synthesis was unable to suppress growth ofE. amylovoraindicating that the additional inhibitory effect
is due to production of bacilysin, a dipeptide whose synthesis does not depend on Sfp. We propose to
useB. amyloliquefaciensstrains with enhanced synthesis of difficidin and/or bacilysin for development of
biocontrol agents efficient against fire blight disease.