Bacterial contamination of fresh tomato
fruits is of great concern. From naturally infected
tomato fruits showing dark brown irregularly shaped
spots, 36 bacterial isolates were recovered and
identified on phenotypic characteristics and sequences
of the gene encoding the 16S rRNA. Five isolates
showing spots on tomato fruits in the pathogenicity
test with healthy tomato fruits belong to the genus
Serratia on the basis of phenotypic characteristics.
One representative isolate of these has been further
identified as a Serratia rubidaea by sequencing of the
16S rRNA gene. This is the first evidence showing
that a S. rubidaea strain can cause spots on tomato
fruits. Virulence of the S. rubidaea was also confirmed
by the production and secretion of a large
variety of enzymes capable of degrading the complex
polysaccharides of the plant cell wall and membrane
constituents. Nineteen bacterial isolates of the 36 did
not induce any spot symptoms in a pathogenicity test
on artificially infected tomato fruits although these are
known as phytopathogenic bacteria. Five of these 19
bacterial isolates were identified as Ralstonia species
on the basis of biochemical tests. Sequencing of the
16S ribosomal gene of one representative isolate
revealed that the isolate is closely related to Ralstonia
solanacearum. Six isolates of the 19 were related to
Xanthomonas vesicatoria on the basis of biochemical
tests and eight were related to the Enterobacteriaceae.
One representative isolate of the Enterobacteriaceae
could be identified by the 16S rRNA gene as
Enterobacter cloacae subsp. dissolvens. The 12 other
strains were related to Proteus mirabilis based on the
16S RNA gene sequence of one representative isolate.
The isolates related to P. mirabilis did not produce
any symptoms on artificially infected tomato fruits.
The nucleotide sequences of S. rubidaea strain E9, E.
cloacae strain E23, P. mirabilis strain E11, and R.
solanacearum strain E15 have been deposited in the
GenBank nucleotide sequence database under accession
numbers HM585373 to HM585376.