Endophytic bacteria in cacti native to a Brazilian semi-arid region

Aim To identify endophytic bacteria in Brazilian cacti, and to evaluate the effects of those bacteria on the growth of Cereus jamacaru seedlings and phosphate solubilization in vitro. Methods Samples of roots and stems of C. jamacaru and Melocactus zehntneri were collected from the Aiuaba ecological Station in Brazilian semi-arid region. Bacterial isolates were cultured in semi-solid N-free media and growth in Pikoskaya's and GL media phosphate solubilizing. In seedling assays, strains of Rhizobium (CAC 01), Enterobacter (CAC 02 and CAC 11), Pseudomonas (CAC 03) and Burkholderia (CAC 07 and CAC 10) were tested. Results Culturable endophytic bacteria were observed in all samples from cacti, but the populations were low. Representatives of eight groups were identified based on partial sequences of 16S rDNA and were related to Rhizobium, Burkholderia, Enterobacter, Pseudomonas, and Pantoea species. The colonization of seedlings with endophytic bacteria was observed, but biomass accumulation did not show a significant increase. All strains were able to grow on solid Pikoskaya's medium. Conclusions The bacterial strains didn't increase significantly the cactus biomass during 6 months of cultivation, but showing potential phosphate solubilizing activity.