BIOLOGICAL PROPERTIES OF SOME NITROGEN-FIXING ASSOCIATIVE ENTEROBACTERIA

Enterobacteria isolates from potato tubers were able to fix nitrogen, to protect plants against phytopathogens and to produce phytohormones thus increasing the plant yield. These isolates were previously phenot ypically identified as Erwinia carotovora; however, they differed from typical E. carotovora in a number of biological characteristics and w ere found to be nonphytopathogenic (avirulent) due to the lack of pect ate lyase activity. A data matrix, containing 31 strains and 105 biolo gical characteristics was used for computer cluster analysis. The avir ulent strains formed a separate cluster more closely related to Klebsi ella spp. strains (with a 0.67 level of similarity) than to typical ph ytopathogenic bacteria of the E. carotovora group (with a 0.48 level o f similarity). A phylogenetic analysis based on restriction polymorphi sms of an amplified ribosomal DNA spacer region revealed that the avir ulent strains studied here were different from all Erwinia, Klebsiella and other enterobacteria species strains. The AP PCR/hybridization te chnique showed cross homology of amplified DNA of these avirulent stra ins and a lack of such homology with the DNA from strains of other spe cies. Numerical taxonomy data, rDNA analysis and AP PCR/hybridization assays confirmed that these avirulent bacteria may be regarded as an i ndependent group of enterobacteria.