A biofilm used as ultraviolet dosimeter

Abstract

An UV-dosimeter has been developed for routine measurements which mainly weights the various components of the spectrum in relation to their damaging effects on a microorganism. For this purpose a biofilm was constructed, comprising dried spores of Bacillus subtilis (wild-type or DNA repair defective strain), immobilized on transparent polyester plastic sheets. After irradiation, the biofilm was incubated in a growth medium. The proteins, synthesized by immobilized microorganisms after spore germination and several cell divisions, were stained and determined by photometry, giving a measure of the biological activity. The "biological effective dose" was determined from a calibration curve. It reflects the dose equivalent to that of the calibration source producing the same effect. The UV-response of the biofilm is additive and follows the reciprocity law in the range of fluence rates investigated. The response is nearly independent of temperature within the range of 20 °C to +70 °C as well as of humidity between about 37 % and 80 % relative humidity. Storage for up to 9 months at < 70 % relative humidity and room temperature does not influence the viability of the spores to a significant rate.