Flow cytometry analysis of low/high DNA content (LNA/HNA) bacteria as bioindicator of water quality evaluation

Abstract

Anthropogenic activities such as agriculture, industry and climate change have been creating an enormous pressure on freshwater ecosystems leading to its degradation. Because the Water Framework Directive (WFD; main EU instrument for ecological water quality assessment) is costly and time-consuming, the main goal of this study was to use the scoring by flow cytometry (FCM) of bacterial communities with high DNA content (HNA) and low DNA content (LNA), a fast and easy methodology, as bioindicators. To portray this study, 3 sampling sites of Caima river with different levels of environmental impact (site 1 – no anthropogenic impacted site; site 2 – downstream wastewater treatment plant and site 3 – downstream a deactivated mine) were analysed along the 4 seasons of the year 2017 (winter, spring, summer and autumn). The ecological status of the sampling sites was accessed following the methodology described by WFD and biotic index results obtained for macroinvertebrate and periphyton communities, as well as the BOD5, were compared with the bacterial community scored as HNA and LNA. Bacteria community analysis showed high bacteria density at site 2 corresponding to high amounts of organic input by the wastewater treatment plant. Also, HNA bacteria were found to be in higher quantities at site 2, related to an increase of nutrients, while LNA bacteria were more prominent in river headwater, corresponding to an oligotrophic environment. Correlations between biological indices and bacteria community composition were very strong, showing that bacteria communities may serve as indicators of water quality assessment. Although this FCM technique provide good responses, further investigations are needed to confirm the feasibility of this method.