In the past two decades emerging and re-emerging plant pathogens have caused new threats to the
production of several economically important crops, one among them is P. syringae pv. actinidiae
(PSA) which causes canker or leaf spot on kiwifruit plants. PSA enters plant through wounds and
remains dormant in cortex tissue of the branches, and spreads in the tissue to cause severe
symptoms from winter to early spring. The disease can be visualized by brown discoloration of
buds, dark brown angular spots surrounded by yellow haloes on leaves, cankers with white to
reddish (oxydation) exudate on twigs and trunks, fruit collapse, wilting and eventually plant
mortality. Current control methods have their own significance in disease control, however there
is considerable lack of clear understanding of PSA pathogenicity. Virulence of plant pathogens
often relies on the synchronized/coordinated expression of pathogenicity factors via quorum
sensing (QS). Therefore, investigations on QS in PSA may lead to develop novel disease control
strategies and reliable methods to curb the disease. It is currently unknown whether PSA produces
a QS signal molecule thus the aim of this thesis is to investigate whether PSA possesses a QS
system. As genome mining did not reveal the presence of any currently known QS system, this
study initially by metabolomics was aimed at identifying potentially low molecular weight
secondary metabolite QS molecules produced by PSA. Azelaic acid was discovered to be produced
by PSA, this is the first report of azelaic acid production by bacteria. The characterization and
possible role of azelaic acid in QS is presented. Since azelaic acid is ubiquitous in nature, in
addition to determining its biological role, the catabolism of azelaic acid in bacteria using the
efficient degrader Pseudomonas nitroreducens DSM 9128 was also studied
