Metabolic aspects of plant interaction with commensal methylotrophs

Abstract

Pink-pigmented, facultatively methylotrophic bacteria (PPFM’s) are normally associated with seeds and leaves of soybean and all other plants we have examined. We became aware of PPFM’s as covert colonizers of callus cultures. PPFM’s produce a constitutive urease which appears to contribute to the ‘background’ urease of callus cultures and unifoliate leaves of a mutant defective in the structural gene (Eu4) for the plant-encoded ubiquitous urease isozyme (Polacco et al., 1989; Holland and Polacco, 1992). A second class (class II) of soybean mutants, which have pleiotropically lost the activities of both the ubiquitous urease and the embryo-specific ureases (Meyer-Bothling et al., 1987) harbors PPFM’s which are deficient in urease and hydrogenase activities in planta. The bacteria are transiently urease- and hydrogenase-negative when cultured away from the plant, and re-acquisition of these activities is accelerated by supplemental nickel (Holland and Polacco, 1992).