BACTERIAL PHOTOPROTECTION THROUGH EXTRACELLULAR CADMIUM-SULFIDE CRYSTALLITES

Ultraviolet light and the heavy metal, cadmium, both have toxic effect s on many microorganisms, In this communication we describe a method b y which the bacterium Klebsiella aerogenes surmounts both problems usi ng one biological process: the synthesis of cadmium sulfide (CdS) crys tallites. These semiconductor particles absorb radiation in the UV spe ctral region and therefore, when K. aerogenes produces extracellular C dS material in response to environments containing cadmium ions, a pho toprotective layer is formed. The effect of UVA radiation on cultures of Klebsiella aerogenes was monitored using electron microscopy, energ y-dispersive X-ray analysis and electronic spectroscopy. The results s how that at wavelengths 320 nm equal to or less than lambda equal to o r less than 400 nm, a photoprotection period of between 4 and 6 h is i nduced, which eventually fails due to photodegradation of the semicond uctor layer to metallic cadmium and elemental sulfur.