PHENOTYPIC AND GENETIC DIVERSITY OF PAENIBACILLUS AZOTOFIXANS STRAINSISOLATED FROM THE RHIZOPLANE OR RHIZOSPHERE SOIL OF DIFFERENT GRASSES

Fifty-three strains identified as Paenibacillus azotofixans were isola ted from the rhizoplane and rhizosphere of different grasses and from soil. To study the diversity within this species, four approaches were used: assessment of homology with a nifKDH probe in hydridization exp eriments; use of a selected 20-mer primer to produce RAPD profiles and of BOX-PCR to generate genomic ginferprintings; and phenotypic tests using the API50CH system. The API tests performed with the 53 P. azoto fixans strains showed that all strains produced acid from 15 carbohydr ates; using six other carbohydrates (sorbitol, dulcitol, tagatose, sta rch, glycogen and D-arabitol), the strains could be divided in five gr oups of related strains. All strains tested showed homology to Klebsie lla pneumoniae nifKDH genes, resulting in 14 different hybridization p atterns with this probe, Using RAPD-fingerprinting with one appropriat e primer, 23 different amplification patterns were observed. The BOS-P CR approach confirmed the grouping suggested by the RAPD fingerprintin g, A comparison of the 53 strains by similarity mat ris analysis using the data obtained in all approaches resulted in a phenogram, grouping them into five broad groups at 74% similarity and into 27 subgroups a t 94% similarity. At 100% similarity, 31 groups of strains could be fo rmed, indicating a high degree of diversity among the strains tested. Overall, the diversity was independent from the origin of strains, sin ce a variety of different groups was isolated from each plant studied. However, some clusters were dominant in wheat and sugarcane samples. The results indicated that the methods used here are sensitive indicat ors of diversity among the strains studied and can be applied as effic ient and reliable means for further ecological and biogeographical stu dies.