Effects of Ultraviolet Radiation on the Individual Spores of Two Biological Insecticides as Revealed by Single‐Spore Optical Analysis

Although the germicidal effects of UV radiation are well documented, its impact on the germination behavior of individual spores remains poorly understood. This study employed single-spore optical analysis to investigate how UV exposure affects Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus (Ls) spores and their germination. Following 2-10 min of UV treatment, spore viability declined to 76%-16% for Bt and 74%-3.3% for Ls. Increased exposure was associated with reduced CaDPA content, decreased intensity at 1280 cm^-1, and increased band ratios (1243/1257 cm^-1 and 1662/1650 cm^-1), indicating structural alterations in amide III and I regions of proteins due to radiation. UV exposure delayed germination responses to both nutrient and non-nutrient germinants, as evidenced by prolonged lag times, extended CaDPA release, and slower cortex lysis. Furthermore, germination heterogeneity increased among individual spores. Collectively, these findings suggest UV radiation likely impairs germination-related proteins, leading to delayed and desynchronized spore germination.