The impact of dose, irradiance and growth conditions on Aspergillus niger (renamed A. brasiliensis) spores low-pressure (LP) UV inactivation

Abstract

The use of Aspergillus niger (A. niger) fungal spores as challenge organism for UV reactor validation studies is attractive due to their high UV-resistance and non-pathogenic nature. However A. niger spores UV dose-response was dependent upon sporulation conditions and did not follow the Bunsen–Roscoe Principle of time-dose reciprocity. Exposure to 8 h of natural sunlight for 10 consecutive days increased UV resistance when compared to spores grown solely in dark conditions. Application of 250 mJ cm⁻² at high irradiance (0.11 mW cm⁻²) resulted in a 2-log inactivation; however, at low irradiance (0.022 mW cm⁻²) a 1-log inactivation was achieved. In addition, surface electron microscopy (SEM) images revealed morphological changes between the control and UV exposed spores in contrast to other well accepted UV calibrated test organisms, which show no morphological difference with UV exposure.

Keywords:

• Aspergillus niger
• Bunsen–Roscoe law
• reactor validation
• scanning electron microscopy
• ultraviolet disinfection

Acknowledgments

The authors gratefully acknowledge Dr. Zahava Barkay from Tel Aviv University Center for Nanoscience and Nanotechnology for her kind assistance in the SEM analyses.