The nutrition of phytopathogenic bacteria; the genus Agrobacterium.

The nutritional requirements of the tumor-inducing phytopathogenic bacteria and soil saprophytes which Conn (1942) has placed in the genus Agrobacterium have received somewhat more attention than have the requirements of most of the other groups of plant-disease bacteria. It is clear from the literature (Sagen, Riker, and Baldwin, 1934; Riker, Lyneis, and Locke, 1941; Hofer, 1941) that the crown-gall bacterium, Agrobacterium tumefaciens, and the common soil saprophyte, Agrobacterium radiobacter, grow well in solutions containing only ammonium or nitrate nitrogen and any of a number of carbon sources. On the other hand, the remaining two species at present in this genus, the hairy-root organism, Agrobacterium rhizogenes, and the cane-gall bacterium, Agrobacterium rubi, are reported to have somewhat more complex nutritive requirements. For example, Sagen, Riker, and Baldwin (1934) summarize their study of A. rhizogenes by stating that it "seems to lack the ability of P. tumefaciens and B. radiobacter to utilize the simpler nitrogenous compounds." Similar observations are recorded for A. rubi by Pinckard (1935) and Hildebrand (1940). Inasmuch as knowledge of the exact nutrition of this group may be useful in interpretations of the systematics and general physiology of the genus, as well as provide source material for eventual evaluation on the possible interrelationship of microbial nutrition and virulence (McNew, 1938; Van Lanen, Baldwin, and Biker, 1940), a study of the four Agrobacterium species was undertaken. At the same time some observations were made on the nutritive requirements of Bacterium pseudotsWae and Agrobacterium gypsophilae, two species which have been placed in an Appendix to Agrobacterium in the forthcoming sixth edition of Bergey's Manual of Determinative Bacteriology. In general, the objective was prompt, moderate growth in simple solutions of known composition, rather than development as rapid and luxuriant as possible in complex media.