Burkholderia glumae causes rice seedling rot
and grain rot disease. It is genetically unstable in its pathogenicity,
and colony morphological mutants (CMMs) also
frequently emerge during subculture. In this study, three
types of CMM were isolated during subculture, and we
characterized virulence factors such as phytotoxin, oxalic
acid, and N-acylhomoserine lactone (AHL) productivity
and motility. The CMMs had various phenotypes and loss
of pathogenicity or reduction of virulence on seedlings and
spikelets. Quorum sensing system (QSS) plays a central role
in the virulence of B. glumae. Although the phytotoxin
production and motility were lost or reduced in CMMs,
AHLs were produced normally by 16 h after incubation,
and no mutations were associated with genes for QSS such
as tofI, tofR and qsmR. Thus, QSS in the CMMs seemed to
function normally, with virulence reduced by another
unknown mechanism. Furthermore, culture pH values
decreased in the wild-type strain but increased in the CMMs
at 30 C in Luria–Bertani medium. Since many bacteria
have been known to increase pH values in LB medium,
culture acidification in LB medium may be a specific