Oligotrophic bacteria in a soil of the Caldenal region

This work investigates both the presence and the effect of burning on oligotrophic soil bacteria in a soil of the Caldenal. Two-hundred eighty three oligotrophic bacteria were isolated before and after burning the soil and their morphological and physiological characteristics examined. Moreover, the resistance to five antibiotics, six heavy metals and three stains in two concentrations was determined. Fire did not reduce the number of oligotrophic bacteria/g soil and neither affected the types of bacteria that colonized the soil surface (0-5 cm). A high proportion of the isolates were Gram negative non spore forming bacteria (65 %). All the bacteria were sensitive to brilliant green stain and resistant to cefuroxime, penicillin G and rifampicin in the highest dosis essayed (20 mu g/ml). Cd and Cu were the most inhibiting heavy metals. Based on the results obtained the oligotrophic soil bacteria were classified in eight different collections. The results show that oligotrophic bacteria are dominant organisms in the biotic structure of the Caldenal soil.