Bacterioplankton community composition in Portuguese water bodies under a severe summer drought

In 2005, a severe drought occurred in Portugal, with several reservoirs becoming dry in the southern region. A set of 20 Portuguese water bodies were analysed through denaturing gradient gel electrophoresis (16SrDNA-DGGE) and DNA sequencing to assess its bacterioplankton diversity under these particular conditions. Environmental parameters were determined to assess the trophic conditions of each water body. Most water bodies fell into themeso- to eutrophic andhypereutrophic state. In general, the levels for conductivity, pH and total suspended solids were higher than the average data from previous years. Dominant phylotypes belonged to Cyanobacteria, Actinobacteria Alphaproteobacteria, Betaproteobacteria and Bac-teroidetes groups. Despite the geographic distance, common phylotypes could be recorded among water bodies. Bacteroidetes dominated at Sousa River and were related to high nutrient levels. Cyanobacteria dominated at Alentejo reservoirs and correlated with higher conductivity values. However, Actinobacteria showed ubiquitous phylotypes throughout several samples, suggesting its persistence over geographically distant water bodies. This study showed a clear deterioration of water quality, from a physico-chemical point of view; furthermore, dominance of Cyanobacteria and Actinobacteria in reservoirs used for drinking water supply were also detected, which may become a concerning issue. However, the most severe bacterial community composition variations between summer 2005 and others were mainly related to higher water residence times. Thus, along with the expected intensification of drought episodes, with severe effects particularly in Southern Europe, it is clearly predictable an intensification in risks for water quality maintenance and even Public Health.