BACTERIA DIVERSITY AND MORPHOLOGY IN DEEP ULTRAOLIGOTROPHIC ANDEAN LAKES: THE ROLE OF ULTRAVIOLET RADIATION ON VERTICAL DISTRIBUTION

C. CORNO; MODENUTTI, B.; CRISTIANA CALLIERI; BALSEIRO, E.; ROBERTO BERTONI; CARAVATI, E.

Niza, Francia

Congreso; ASLO Annual Meeting 2009; 2009

ASLO

We analysed the bacteria relative diversity by Denaturating Gradient Gel Electrophoresis (DGGE), and the morphological distribution (cocci or rods vs. filaments >7µm) in relation to vertical profiles of different light wavelengths (UVR and PAR), temperature, nutrients, and nanoflagellate and ciliate abundances, in eight ultraoligotrophic Andean lakes (Patagonia, Argentina). The overall bacterial community composition was similar among the lakes and at different depths along the euphotic zone of each lake. Nevertheless the relative proportion of filaments to total bacterial biovolume was higher in upper layers with higher UVR, showing a monotonical decrease with depth. Lakes with lower UVR diffuse extinction coefficient (305 nm) showed a greater proportion of filaments. Statistical analysis showed a strong correlation between UVR and filament proportion while neither nanopredator abundance, nor predation pressure, nor resources (dissolved nutrients) could explain the high proportion of filamentation in the near-surface layers. We propose that UVR plays an important role stimulating bacterial filamentation, particularly in lakes with high UVR penetration like the deep Andean transparent lakes.