COMPARISON OF PAENIBACILLUS-AZOTOFIXANS STRAINS ISOLATED FROM RHIZOPLANE, RHIZOSPHERE, AND NON-ROOT-ASSOCIATED SOIL FROM MAIZE PLANTED IN 2DIFFERENT BRAZILIAN SOILS

Paenibacillus azotofixans is a nitrogen-fixing bacterium often found i n soil and in the rhizospheres of different grasses. In this study, tw o Brazilian clay soils were planted with cross-hybrid maize (BR-201) a nd four stages of plant growth were analyzed to characterize the P. az otofixans populations present in the rhizoplanes, rhizospheres, and no n-root-associated soils (herein called nonrhizospheres). A total of 10 6 strains were isolated and identified as P. azotofixans with an API 5 0CH kit, by classical biochemical tests, and via the use of specific p rimers based on the 16S rRNA gene in PCRs. To compare the isolated str ains, phenotypic characteristics were determined and three different p robes were used in hybridization experiments: two nif probes and one p robe comprising a 0.58-kb fragment cloned from the P. azotofixans C3L4 genome, These results were used to construct a dendrogram, in which t wo main clusters could be observed. One cluster contained exclusively strains from Varzea soil, and the other contained the majority of stra ins from Cerrado soil. The 60 strains from Varzea soil and the 46 stra ins from Cerrado soil were further analyzed with REP and BOX primers, respectively. Based on the patterns obtained, it,vas possible to ident ify 21 different groups among strains from Varzea soil and 4 different groups among strains from Cerrado soil. These different patterns were tested by multivariate analysis of variance, and differences in the p opulations of P. azotofixans during the four stages of plant growth we re demonstrated. Moreover, strains isolated from the rhizoplanes, rhiz ospheres, and nonrhizospheres of maize planted in Cerrado and Varzea s oils were shown to be statistically different; the diversity of P. azo tofixans strains was affected by the soil type.