Using flow cytometry for bacterioplankton community analysis as a complementary tool to Water Framework Directive to signal putatively impacted sites

Abstract

Metal contamination, as well as pesticides, organic matter and nutrient input are main factors leading to freshwater ecosystems degradation. The Water Framework Directive (WFD) was implemented within the European Union with the ultimate goal of promoting a good ecological status in all European waterbodies. However, the broad implementation of the bioassessment behind WFD is costly and time-consuming and the search for complementary methodologies has been given significant attention. In this context, the main goal of this study was to evaluate whether flow cytometry (FCM) and denaturing gradient gel electrophoresis (DGGE) can be used as cellular/molecular tools to efficiently assess riverine bacterioplankton communities and relevantly inform on the ecological quality of these ecosystems. Caima river was chosen as case study using three sampling sites reflecting different levels and types of contamination (point-source organic and metal input). Both bacterioplankton community assessment approaches (DGGE and FCM), as well as macroinvertebrate and periphyton communities were consistent in signaling organic contamination. The putatively metal-loaded site bears some contradictory results depending on the community focused, possibly due to the overall low levels of metals actually found and seasonality. When comparing the two bacterioplankton community analysis tools, DGGE and FCM, the results obtained were essentially coherent, with FCM being simpler, faster and still accurate for screening bacteria communities via quantification of bacteria of high and low DNA content. This highlights the suitability of the FCM approach for prioritization of contaminated sampling sites and reinforces the suitability of using bacterioplankton communities as the focus of rapid tools to complement bioassessment sensu the WFD methodology, e.g. assisting the prioritization of potentially impacted areas.

Keywords: Bacterioplankton community analysis; DGGE; Flow cytometry; Multivariate analysis; River ecological status evaluation.