AIM: To screen mobile genetic elements (MGE) in the bacterium which caused decay of field-grown onion
bulb and to study an integron and gene cassettes associated. METHODS: Polymerase chain reaction (PCR)
and PCR products sequencing were used for both the bacterium and MGE identification. Terminally-labeled
Restriction Fragment Length Polymorphism (TRFLP) analysis was performed for detection of any bacterium
in the onion bulb tissue. RESULTS: The bacterium, which caused field-grown onion decay, was identified
by nucleotide sequence analysis of the 16S rRNA genes to be S. marcescens known as phytopathogen.
However, this isolate did not respond to specific primers designed for pathogenic strains. Inoculation of
onion (Allium cepa L.), Arabidopsis thaliana (L.) Heyhn, and lettuce (Lactuca sativa) seeds resulted in
biomass promotion of symptomless plants. PCR revealed the presence of a class 1 integron in S. marcescens
IMBG291 which represents the first isolation of this integron in phytopathogenic Serratia species. The gene
cassettes harbored by the integron have been represented with the promoterless genes encoded formiminoglutamate
deiminase and ascorbate-specific phosphotransferase system enzyme IIC, and with additional
three senseless sequences flanked by a 59-bp element. CONCLUSION: S. marcescens IMBG291 exhibited plant
growth promotion or pathogenicity, depending on the environmental situation, due to horizontally acquired
new gene cassettes located in the integron.