Electrophysiological membrane characteristics of the salt tolerant Plantago maritima and the salt sensitive Plantago media

Plasmid pUCD607 was mobilized into the biocontrol agent Enterobacter cloacae strain E6 by conjugation and the resultant strain, E6(pUCD607), was bioluminescent. Biocontrol of Pythium ultimum by E6(pUCD607) was similar to that of the parent strain, E6. The location of E6(pUCD607) in the soil and in the rhizosphere of lettuce was readily determined by pressing agar medium against plant roots in a root box, allowing the bacteria to grow overnight on the medium, and detecting the presence of bioluminescence by autophotography. There was a positive, linear correlation between population sizes determined by dilution plating and the quantity of light emitted due to bioluminescence. However, both the intercept and slope of this line varied among experiments possibly due to the differing physiological states of cells recovered from soils. The amount of light emitted by the bioluminescent strain E6(pUCD607) was not quantitative. This technique is useful for qualitative determinations of populations and for photographically locating bacteria.