PHYSIOLOGICAL CHARACTERIZATION OF Bacillus spp. STRAINS FROM POTATO (Solanum tuberosum) RHIZOSPHERE

Bacillus is an abundant genus in the rhizosphere of many crops due to its spore formation capacity that gives it an advantage to survive in the rhizosphere. In the present study we worked with 43 Bacillus spp. previously isolated from potato rhizosphere of two highland zones in Peru. We described the morphological characteristic of their colonies and tested them for their physiological and biochemical characterization. Almost all Bacillus strains belong to the "Bacillus subtilis" group. Also acid pH test plate (4 and 5.5) and low temperature plate test (4 degrees C, 10 degrees C, 15 degrees C and 20 degrees C) were done. Of the 43 tested strains only one grew at 4 degrees C; therefore, 99% grew at 10 degrees C, 100% grew at 15 degrees C and 20 degrees C. On the other hand, 100% of the strains grew at pH 4 and 5.5, which indicates an adaptation to acid pH. The evaluation of the growth levels at low pH and low temperature in time reveals a two-phase pattern that could be explained by small lag periods in stress conditions. Due to the differences in the physiological adaptation among strains of the same species; the occurrence of a great intraspecific diversity of Bacillus isolated from potato crop rhizosphere can be suggested. We also found correlations between low temperatures in the isolations zones and a better growth level at 20 degrees C in the plates tested.