Natural strategies for ultraviolet resilience: lessons from slime moulds

ABSTRACT Ultraviolet (UV) radiation exerts strong selective pressures on microbial life, yet many microorganisms display extraordinary resistance, revealing strategies that may be broadly useful for understanding survival under extreme stress. We systematically examined how UVA, UVB and UVC affect two slime mould species with contrasting pigmentation, Physarum polycephalum and Badhamia utricularis. Across more than 20 000 behavioural assays, we quantified growth, locomotion, photoavoidance, recovery capacity, fusion outcomes and revival from dormancy. UVB emerged as the most deleterious wavelength, causing rapid and sustained declines in growth and motility, while UVC produced intermediate, species-dependent effects, and UVA had a negligible short-term impact, though prolonged exposure over weeks eventually reduced locomotion. Damage was spatially restricted to irradiated plasmodial regions via compartmentalization but could spread through cytoplasmic fusion with stressed partners. Intermittent dark intervals enabled partial recovery, particularly from UVC, consistent with efficient photorepair, whereas UVB damage was more persistent. Strikingly, both species revived from sclerotia with near-perfect success even after a full week of continuous UV exposure, underscoring dormancy as a robust survival strategy. Badhamia utricularis consistently outperformed P. polycephalum. These findings reveal that slime moulds deploy wavelength-specific, species-dependent and state-dependent strategies to withstand UV stress, with rapid damage compartmentalization limiting immediate dysfunction and dormancy ensuring long-term survival under extreme irradiation.