Phenotypic Characterization of a Mutant of Burkholderia cepacia MRT11 Defective in Rhizosphere Competence

Abstract

A mutant (RCD1) defective in rhizosphere competence of Burkholderia cepacia MRT11, an effective root colonizer of radish, was isolated by successive single colony transfers. The ability of RCD1 to colonize radish root was reduced to about one % of that of the wild type strain MRT11. The properties considered to be involved in the colonization of the roots were compared between the two strains. There were no significant differences between the two strains in motility, chemotactic response to root exudates, cell surface hydrophobicity, adherence to roots, and in vitro antibiosis to fungal pathogens. There were also not significant differences in the growth of most media used in this study, such as nutrient broth, minimum medium with glucose, galactose, or casamino acids as the sole carbon source. However, the growth of MRT11 in radish root exudate was greater than that of RCD1, suggesting that the ability to utilize root exudates might be responsible for part of the rhizosphere competence of B. cepacia MRT11. The properties that were impaired in RCD1 are further discussed in relation to the utilization of root exudate.