Biological activity and colonization pattern of the bioluminescence-labeled plant growth-promoting bacterium Kluyvera ascorbata SUD165/26

Kluyvera ascorbata SUD165/26 is a spontaneous siderophore-overproducing mutant of K. ascorbata SUD165, which was previously isolated from nickel-contaminated soil and shown to significantly enhance plant growth in soil contaminated with high levels of heavy metals. To develop a better understanding of the functioning of K. ascorbata SUD165/26 in the environment, and to trace its distribution in the rhizosphere, isolates of this bacterium were labeled with either green fluorescent protein or luciferase. When the plant growth-promoting activities of the labeled strains were assayed and compared with the activities of the unlabeled strain, none of the monitored parameters had changed to any significant extent. When the spatial colonization patterns of the labeled bacteria on canola roots were determined after seed application, it was observed that the bacterium was tightly attached to the surface of both roots and seeds, and formed aggregates. The majority of the bacterial population inhabited the upper two thirds of the roots, with no bacteria detected around the root tips.