Resumo

Plant growth promoting rhizobacteria (PGPR) are able to increase health and vigor of a host plant by displaying phenotypic traits that help plant thrive in the environment. This natural interaction between plant and bacteria is already used at industry, but there are many unknown factors that act on the occurrence and interaction of plant growth promoting (PGP) traits that may affect bacterial inoculation efficiency in the field. On this study, independent datasets of bacteria isolated from several plants and soils were compiled in a single, comprehensive analysis about the occurrence of PGP traits. Using Categorical Principal Component Analysis, a collection of 2,212 diazotrophic isolates was analyzed. This allowed simultaneous plotting of 13,272 data entries concerning soil nutrients, bacterial niche colonization, bacterial genera (identified by 16S rRNA partial gene sequencing), indolic compounds production, phosphate solubilization, and siderohphore production. Chemical soil characteristics (P, K, clay content, organic matter, and pH) were used to classify soils by overall richness, with a Principal Component Analysis. Association between the different levels of PGP traits with other PGP traits, soil richness, niche, and bacterial genera were tested with the chi-square statistic and adjusted residual analysis. We show that indolic compounds production increases as soil richness increases, while phosphate solubilization and siderophore production increases as soil richness decreases. The generated plot allows us to divide the bacteria in three functional clusters: Nutrient solubilizers, phytohormone producers, and other PGPRs. These other PGPRs are expected to be related to PGP traits that were not analyzed, such as nitrogen fixation and antibiotic activity. We also show that some of the 39 genera analyzed are significantly associated to PGP traits, but these associations can be affected by niche colonization or soil richness. Bacteria from Burhkolderia genus acted as very good nutrient solubilizers, while isolates from the Enterobaceae family were good indolic compound producers, with the genus Klebsiella presenting great phenotypic plasticity according to environmental conditions. Individual analysis of variation inside each genus is currently under way. These results could be applied for directed PGPR bioprospection and application.