Pk. Chakrabarty et al., PLASMID-BORNE DETERMINANTS OF PIGMENTATION, EXOPOLYSACCHARIDE PRODUCTION, AND VIRULENCE IN XANTHOMONAS-CAMPESTRIS PV MALVACEARUM, Canadian journal of microbiology, 41(8), 1995, pp. 740-745
Three plasmids of 55.0, 31.2, and 7.4 kb, designated as pXCM18-I, pXCM
18-II, and pXCM18-III, respectively, were identified and isolated from
strain HR13B/2 of Xanthomonas campestris is pv. malvacearum. The bact
erium was cured of all three plasmids in high frequency (3.1%) with he
at (42 degrees C). The cured strains were nonmucoid and light yellow a
nd were greatly impaired in exopolysaccharide production and virulence
. Transformation of a cured strain using a mixture of purified plasmid
DNA from HR13B/2 resulted in colonies carrying all six possible combi
nations of the three plasmids. Of the transformants, two morphological
ly distinct colony types were observed. The first type of transformant
s were mucoid and deep yellow, not distinguished from wild-type coloni
es in morphology, and fully complemented for exopolysaccharide product
ion. These transformants invariably carried pXCM18-II. The second type
of transformants were not distinguished from the untransformed strain
in morphology but were found to be transformed after screening for pl
asmid content. These transformants carried either pXCM18-I, pXCM18-III
, or both, but never pXCM18-II. In pathogenicity tests, each of the th
ree plasmids restored virulence significantly, and additively, with pl
asmid pXCM18-I playing a predominant role.