Diversity in UV sensitivity and recovery potential among bacterioneuston and bacterioplankton isolates.

Aims:  To assess the variability in UV-B (280–320 nm) sensitivity of selected bacterial isolates from the surface microlayer and underlying water of the Ria de Aveiro (Portugal) estuary and their ability to recover from previous UV-induced stress. Methods and Results:  Bacterial suspensions were exposed to UV-B radiation (3·3 W m−2). Effects on culturability and activity were assessed from colony counts and 3H-leucine incorporation rates, respectively. Among the tested isolates, wide variability in UV-B-induced inhibition of culturability (37·4–99·3%) and activity (36·0–98·0%) was observed. Incubation of UV-B-irradiated suspensions under reactivating regimes (UV-A, 3·65 W m−2; photosynthetic active radiation, 40 W m−2; dark) also revealed diversity in the extent of recovery from UV-B stress. Trends of enhanced resistance of culturability (up to 15·0%) and enhanced recovery in activity (up to 52·0%) were observed in bacterioneuston isolates. Conclusions:  Bacterioneuston isolates were less sensitive and recovered more rapidly from UV-B stress than bacterioplankton isolates, showing enhanced reduction in their metabolism during the irradiation period and decreased culturability during the recovery process compared to bacterioplankton. Significance and Impact of the Study:  UV exposure can affect the diversity and activity of microbial communities by selecting UV-resistant strains and alter their metabolic activity towards protective strategies.