Isolation and characterization of bacteriophage SBX-1 and its bacterial host, both endemic in soybeans.

A phage, SBX-1, and its bacterial host, Xanthomonas sp. 1, were isolated consistently from roots, internal portions of stems, and leaves of soybean plants. Phage titer in leaves was highly variable. It was very low in seedlings, reached a maximum of 10(4) PFU/ml of sap after 11 weeks of plant growth and again dropped to very low levels. We isolated SBX-1 from plants of all 45 varieties studied, but not consistently from some. Plants of some varieties also carried Xanthomonas sp. 2, which was resistant to infection by SBX-1. The SBX-1 particle has a polyhedral head containing DNA of density 1.709. It has an edge-to-edge diameter of 80 nm and a tail length of 112 nm. The tail has a base plate and spikes. This is the first report of the extensive and continuous occurrence of a phage and its host bacterium in plants.