Clay minerals protect bacteriophage PBS1 of Bacillus subtilis against inactivation and loss of transducing ability by UV radiation

The effect of UV radiation on the survival of and transduction by phage PBS1 of Bacillus subtilis, free or adsorbed on the clay minerals montmorillonite (M) and kaolinite (K), was studied. After free or clay-associated phage (similar to 10(7) PFU.mL(-1)) was irradiated with UV light (254 nm) for 0, 1, 2, 5, 10, and 30 min and then allowed to infect B. subtilis FB300 (thiB4 metA29 argF4 Rfm(r)), the phage was titered, and Met(+) transductants were enumerated on selective media. After 1 min of irradiation, the titer of free and clay-associated phage decreased significantly (similar to 1.6 times for free phage, and similar to 4.9 and 6.8 times for M and K, respectively), whereas the transduction frequency increased significantly (similar to 3 times for free phage and similar to 1.4 and 2.2 times for M and K, respectively). The titer and transduction frequency of clay-associated phage remain essentially constant between 1 and 10 min of irradiation, whereas the titer of free phage decreased by similar to 1 order of magnitude after 5 min of irradiation. When free phage was irradiated for 10 min, the titer and transduction frequency decreased by similar to 2 and 0.5 orders of magnitude, respectively, whereas 30 min of irradiation was necessary to obtain comparable decreases with clay-associated phage. These results indicated that phages are protected to some extent from UV radiation when adsorbed on clay minerals.