SOLAR-RADIATION IS SHOWN TO SELECT FOR PIGMENTED BACTERIA IN THE AMBIENT OUTDOOR ATMOSPHERE

The percentage of pigmented to total bacteria in the outdoor atmospher ic population was studied in the field and in controled laboratory exp eriments to evaluate the effects of solar radiation (SR) on bacterial survival, The field experiments showed that the percentage of pigmente d bacteria positively correlated with SR activity during clear summer days, The percentage was lowest during darkness before dawn and around midnight (ca 33%) and as the SR increased during the day, gradually i ncreased to a maximum of ca 50-60% at noontime to early afternoon and decreased thereafter. In the laboratory the ambient outdoor atmospheri c bacteria impacted on culture plates were exposed to simulated SR and a germicidal light, With increased exposure, more nonpigmented bacter ia were killed and the percentage of pigmented bacteria gradually incr eased, These observations suggest an inverse relationship between the atmospheric bacterial survival and the percentage of pigmented bacteri a contained therein, thus supporting the notion that pigmentation migh t provide protection for outdoor atmospheric bacteria from sunlight da mage, As a consequence, viable pigmented bacteria (and other UV-resist ant forms) in the atmosphere could be enriched under areas of stratosp heric ozone depletion.