ISOLATION AND SEQUENCE-ANALYSIS OF THE PSEUDOMONAS-SYRINGAE PV TOMATOGENE ENCODING A 2,3-DIPHOSPHOGLYCERATE-INDEPENDENT PHOSPHOGLYCEROMUTASE

Pseudomonas syringae pv. tomato DC3481, a Tn5-induced mutant of the to mato pathogen DC3000, cannot grow and elicit disease symptoms on tomat o seedlings. It also cannot grow on minimal medium containing malate, citrate, or succinate, three of the major organic acids found in tomat oes. We report here that this mutant also cannot use, as a sole carbon and/or energy source, a wide variety of hexoses and intermediates of hexose catabolism. Uptake studies have shown that DC3481 is not defici ent in transport. A 3.8-kb EcoRI fragment of DC3000 DNA, which complem ents the Tn5 mutation, has been cloned and sequenced. The deduced amin o acid sequences of two of the three open reading frames (ORFs) presen t on this fragment, ORF2 and ORF3, had no significant homology with se quences in the GenBank databases. However, the 510-amino-acid sequence of ORF1, the site of the Tn5 insertion, strongly resembled the deduce d amino acid sequences of the Bacillus subtilis and Zea mays genes enc oding 2,3-diphosphoglycerate (DPG)-independent phosphoglycero-mutase ( PGM) (52% identity and 72% similarity and 37% identity and 57% similar ity, respectively). PGMs not requiring the cofactor DPG are usually fo und in plants and algae. Enzyme assays confirmed that P. syringae PGM activity required an intact ORF1. Not only is DC3481 the first PGM-def icient pseudomonad mutant to be described, but the P. syringae pgm gen e is the first gram-negative bacterial gene identified that appears to code for a DPG-independent PGM. PGM activity appears essential for th e growth and pathogenicity of P. syringae pv. tomato on its best plant .