An image analysis method for determination of spatial colonization patterns of bacteria in plant rhizosphere

A method that allows the rapid visualization of bacterial spatial colonizat ion patterns on roots for the determination of general colonization trends was developed. This method, which analyzes images of roots, and bioluminesc ence-enhanced images of bacterial colonization patterns on these roots, was used to study the colonization patterns of seed-applied Enterobacter clonc ae strain E6 on 3-day-old cucumber plants. Conventional dilution-plating me thods indicated that E6 colonized cucumber tap roots in high populations an d that these populations significantly decreased as the distance from the s eed increased. In addition to confirming these observations, image analysis indicated that colonization by E6 significantly decreased on lateral roots as the distance increased horizontally away from the tap root, and that th is bacterium did not evenly cover the most densely colonized regions of the cucumber root system. Results from these experiments indicate that the maj ority of E6 populations on cucumber roots after seed application are limite d to the upper regions of the tap root and that E6 does not effectively col onize other regions of the root system.