Growth of nopaline-utilizing Agrobacterium and Pseudomonas in extracts of crown-gall tumors

Abstract

Two nopaline-utilizing bacteria isolated from the same crown-gall tumor, and identified previously as Agrobacterium tumefaciens and Pseudomonas aureofaciens, were grown in pure or dual culture in various types of media. These included minimal medium with nopaline as the sole carbon and nitrogen source, and intercellular fluid extracted from sunflower or apple. The size of inoculum was similar for the two bacteria, and the ratio of the maximal cell population for P. aureofaciens over that for A. tumefaciens was calculated. This ratio was highest for dual culture in minimal medium, and under these conditions P. aureofaciens utilized most of the nopaline supply. This advantage of Pseudomonas in terms of maximal cell population was reduced for dual cultures in extracts prepared either from uninoculated stems or from tumors that had been induced by the A. tumefaciens isolate. For the two plants studied, the difference between maximal populations of P. aureofaciens and A. tumefaciens was smaller in tumor than in stem extract. The time of disappearance of opines from the tumor extracts was considered in relation with the growth of the two bacteria. Similar analysis was made on cultures involving A. tumefaciens and a mutant pseudomonad deficient in nopaline utilization. These experiments indicated that the differential response of dual cultures of A. tumefaciens and P. aureofaciens to stem or tumor extracts was not due to the presence of opine of the nopaline family in the extracts from crown-gall tumors.