The Role of Nutrition in the Host-Parasite Relationship

Abstract

Seven biochemical mutants of E. aroideae. a bacterial plant pathogen, each requiring 1 or 2 amino acids, were tested for their virulence on the following host spp.: cucumber, potato, turnip, radish, and carrot. Specific mutants were avirulent for certain host spp. Virulent mutants gave a positive growth response when blocks of tissue from the attacked hosts were added as auxanographic supplements; avirulent mutants yielded no response when blocks of tissues from resistant hosts were added as auxanographic supplements. Tissue homogenates from resistant hosts provided the required nutrilites when added as auxanographic supplements to the avirulent mutants. Biochemical mutants of Klebsiella pneumoniae with nutritional requirements comparable to those of the avirulent mutants of E. aroideae gave a positive growth response when tissue blocks from resistant hosts were added as auxanographic supplements. Four biochemical mutants each of E. aroideae and K. pneumoniae with comparable requirements were tested for their relative response to a series of concns. of radish homogenate and solns. of the specific amino acid. The mutants of K. pneumoniae responded better than comparable mutants of E. aroideae to both types of supplementation. The avirulence of specific biochemical mutants for certain host spp. was related to the inability of these mutants to utilize the available concn. of the required nutrilite at the cut surface of the host. The role of nutrition in the host-parasite relationship is discussed.