MULTILOCUS ISOENZYME DIVERSITY AMONG STRAINS OF PSEUDOMONAS-CEPACIA ISOLATED FROM DECAYED ONIONS, SOILS, AND CLINICAL SOURCES

A collection of 59 strains of Pseudomonas cepacia, isolated from a var iety of clinical sources, from decayed onions, and from soils were cha racterized by multilocus isoenzyme electrophoresis and by pathogenic a bility on onion. Fifty-three of the strains were found to be electroph oretically unique accessions (D(T) = 0.981). An overall estimate of ge netic diversity, H(T), of 0.620 was calculated, which is consistent wi th other published reports of diversity for the species. Less than two percent of the observed genetic diversity could be attributed to diff erences between clinical and environmental subpopulations, less than o ne percent to differences between phytopathogenic and nonphytopathogen ic strains. Phytopathogens were absent from the clinical subpopulation . The extreme levels of observed within-group diversity combined with the behavioral differences between clinical and phytopathogenic strain s suggest that isoenzymes are sufficient to function as strain identif iers, and that the present species concept of P. cepacia is too broad.