Abstract
In the summer of 2015, an intense cyanobacterial bloom producing geosmin/2-methylisoborneol (MIB) occurred in the Roxo freshwater reservoir in Alentejo, Portugal. The drinking water supplied from the Roxo water treatment plant (WTP) exhibited an unpleasant odor/taste and a significant cyanobacteria density was detected in the finished water at the exit of the WTP. Cyanobacteria were not evaluated downstream of the WTP, namely, at the city reservoir. The aim of this work was to isolate and characterize viable cyanobacteria present in finished water (exit of the WTP and city reservoir) that withstand conventional water treatment. Treated water samples collected at both sites were inoculated in Z8 culture medium to provide the conditions for putative cyanobacterial growth. After 30 days, filamentous cyanobacteria were observed in cultures inoculated with samples from the exit point of the WTP. Viable trichomes were isolated and identified as Cylindrospermopsis raciborskii by morphometric and molecular analysis. None of the isolates were cylindrospermopsin/microcystin producers, as confirmed by ELISA and amplification of corresponding genes (PS/PKS and mcyA-cd/mcyAB/mcyB). ELISA results were positive for saxitoxin, but saxitoxin and derivatives were not detected by liquid chromatography with fluorescence detection (LC-FLD), nor were their related genes (sxtA/sxtA4/sxtB/sxtM/sxtPer/sxtI). To our knowledge, this is the first report on the establishment of cultures of C. raciborskii that resisted water treatment processes.
Highlights
The Roxo reservoir is a freshwater source located in Alentejo, south Portugal that is used to supply drinking water for the municipalities of Beja (35,854 inhabitants) and Aljustrel (4600 inhabitants).Toxins 2020, 12, 40; doi:10.3390/toxins12010040 www.mdpi.com/journal/toxinsIt is used for irrigation, since it is located in a rural area with important agricultural activity.This region, characterized by a Mediterranean climate, is vulnerable to climate change, namely, severe and prolonged droughts [1,2]
This is the first report of the successful establishment of cultures of C. raciborskii isolated from finished drinking water
According to the identification keys described in EN 15204:2006 [24], cyanobacteria were identified in both samples as C. raciborskii and Pseudanabaena limnetica
Summary
The Roxo reservoir is a freshwater source located in Alentejo, south Portugal that is used to supply drinking water for the municipalities of Beja (35,854 inhabitants) and Aljustrel (4600 inhabitants).Toxins 2020, 12, 40; doi:10.3390/toxins12010040 www.mdpi.com/journal/toxinsIt is used for irrigation, since it is located in a rural area with important agricultural activity.This region, characterized by a Mediterranean climate, is vulnerable to climate change, namely, severe and prolonged droughts [1,2]. It is used for irrigation, since it is located in a rural area with important agricultural activity. This region, characterized by a Mediterranean climate, is vulnerable to climate change, namely, severe and prolonged droughts [1,2]. These conditions have a negative impact on water availability and may favor eutrophication and cyanobacteria blooming [3]. Cell density in raw water ranged between 52,000 and 108,000 cells/mL from
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