Ultraviolet Radiation Induces Filamentation in Bacterial Assemblages from North Andean Patagonian Lakes

Abstract

Through laboratory experiments, we tested whether UV radiation(UVR) induces filamentation in natural bacteria assemblagesfrom North Andean Patagonian lakes. We incubatedwater from three different lakes for 72 h in four separatetreatments: (1) UVR + PAR (photosynthetically active radiation),(2) 50% UVR + PAR, (3) PAR and (4) 50% PAR. Theirradiance levels used in the experiments were equivalent to thoseregistered at the epilimnion of the lakes. In the UVR treatmentsfilamentation was induced after the first 24 h and the proportioncontinued to increase for the next 48–72 h. A comparison of thegross composition and diversity of the entire community (cells>0.2 lm) with bacterial filaments alone (>5.0 lm) showed thatUVR-induced filamentation is not a feature of any particularcluster. By sequencing part of the 16S rRNA gene of thetaxonomic units obtained using denaturing gels, we observed thatstrains in the b-Proteobacteria group were of relatively highimportance in filament formation, followed by Cytophaga–Flavobacterium–Bacteroides, c-Proteobacteria and a-Proteobacteria,whereas Actinobacteria were almost nonexistent in thefilaments. We propose that UVR doses equivalent to those ofAndean lakes produce bacterial morphological changes, and thatall bacterial groups except Actinobacteria can potentially formfilaments.