Morphophysiological characterization of bacteria native to Cerrado soils, isolated from cowpea nodules

Characteristics such as tolerance to pH, temperature, salinity and high aluminum concentration can be verified in rhizobia native to tropical soils. These particularities are relevant to biological nitrogen fixation studies, such as those about Vigna unguiculata L. Walp. (cowpea), which is of great economic importance to family farmers in different parts of Brazil, especially the North and Northeast regions. The objective of this study was to morphologically and physiologically characterize the native bacteria from Cerrado soils in eastern Maranhão, using the cowpea as plant bait. The study was conducted in Caxias (MA) between 2014 and 2015. The isolates were derived from cowpea nodules sampled from three different areas of soil, especially forest composed of babassu and cultivated Manihot esculenta (cassava) and Desmanthus virgatus L. (jureminha). They were morphologically characterized based on their colonies and the following physiological tests: tolerance to high temperatures, acidity, aluminum and high salinity. The isolates showed significant morphological diversity. The physiological tests showed that most of them are resistant to high temperatures, acidity and aluminum toxicity, but only a few are resistant to high salinity.