Role of the intraspecific competition in the regulation of Agrobacterium tumefaciens transconjugant population level in soil experiments

Abstract In microcosms of sterilized soil simultaneously inoculated with Pseudomonas aeruginosa carrying the plasmid R68-45 and the plasmid-free Agrobacterium tumefaciens , transconjugants were detectable after two days of incubation and their number remained constant thereafter. The growth of a transconjugant strain was monitored in sterile soil. When mixed together with the parental strains at high inoculum or when the soil was previously colonized by the donor, the transconjugant was able to grow. If the recipient was the first soil colonizer, the challenging population of transconjugant remained stable at its initial level. We demonstrated the possible role of intraspecific competition in the limitation of transconjugant numbers.