SOLAR-RADIATION HAS A LETHAL EFFECT ON NATURAL-POPULATIONS OF CULTURABLE OUTDOOR ATMOSPHERIC BACTERIA

Ambient heterogenic atmospheric bacteria were collected by impaction d irectly onto nutrient agar surfaces on clear sunny and cloudy days and at night. Samples were then exposed to summer noontime solar radiatio n (SR) for increasing periods of time. Bacterial survival was the leas t for the organisms collected at nighttime and the greatest for those collected during clear sunny days. This result may be due to the inact ivation of SR-sensitive bacterial populations by the ambient SR on cle ar days, and to a lesser extent on cloudy days, leaving only the relat ively resistant populations. This does not occur at night when the SR- sensitive populations have not been reduced. The mixed bacterial speci es populations in the atmosphere do not appear to follow the Bunsen-Ro scoe reciprocity law but integration of pure bacterial components of t he mixed population that do follow the law, could explain the findings . The populations collected in this investigation exhibited SR surviva l functions usable in developing survival and dispersion models of out door atmospheric bacteria and microbial pesticides. Copyright (C) 1996 Elsevier Science Ltd