Method for purification of bacterial endospores from soils: UV resistance of natural Sonoran desert soil populations of Bacillus spp. with reference to B-subtilis strain 168

Endospores of Bacillus spp. were purified from three Sonoran desert soil sa mples by Chelex extraction and NaBr density gradient centrifugation and the ir UV resistances compared with that of B. subtilis strain 168. Natural spo re populations exhibited tight adherence to soil particles which was not re adily overcome by the extraction and purification procedure. It was observe d that spores purified from soil exhibited 2-3 fold higher resistance to UV las measured by the 90% lethal dose, LD90) than did B. subtilis strain 168 grown on NSM, a standard laboratory sporulation medium, and purified by th e same extraction procedure. Cultivation of spore-forming bacteria isolated from soil on NSM resulted in production of spores with essentially identic al UV resistance as strain 168, suggesting that spore UV resistance is infl uenced by the environment in which spores are produced. (C) 1999 Elsevier S cience B.V. All rights reserved.