Diatoms are a group of unicellular algae particularly sensitive to changes that affect their aquatic environment. This is why they are used as bioindicators for the biological monitoring of water quality. However, their microscopic identification in river samples requires a lot of time and skills. Biologists from the University of Geneva (UNIGE), Switzerland, have succeeded in establishing a water quality index based solely on the DNA sequences of the diatoms present in the samples, without needing to identify each species visually. This study, published in the journal Molecular Ecology Resources, presents a revolutionary tool to process a very large number of samples in parallel, allowing wide coverage of the monitored sites in a reduced time and at a lower cost.
Diatoms are a group of unicellular algae particularly sensitive to changes that affect their aquatic environment. This is why they are used as bioindicators for the biological monitoring of water quality. However, their microscopic identification in river samples requires a lot of time and skills. Biologists from the University of Geneva (UNIGE), Switzerland, have succeeded in establishing a water quality index based solely on the DNA sequences of the diatoms present in the samples, without needing to identify each species visually. This study, published in the journal Molecular Ecology Resources, presents a revolutionary tool to process a very large number of samples in parallel, allowing wide coverage of the monitored sites in a reduced time and at a lower cost.
The degree of pollution of rivers resulting from human activities is assessed using different biotic indices. The latter reflect the ecological status of a river based on the quantity and diversity of organisms selected as bioindicators, due to their ecological preferences and tolerance to pollution. This is the case of diatoms, algae consisting of a single cell surrounded by a silica skeleton, recommended by the European Union and Switzerland as one of the ideal bioindicators for rivers and lakes.
The quality of our rivers is determined using the Swiss diatom index (DI-CH), whose value defines the ecological status. “The morphological identification of the different species present in each sample, however, no longer meets the needs of rapid and reliable bioassessment measures introduced to protect aquatic environments. This is why we have tried to develop a new method”, says Jan Pawlowski, professor at the Department of Genetics and Evolution of the UNIGE Faculty of Science.
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Image: Diatoms between 0.01 and 0.02 mm, consisting of a single cell surrounded by an artificially colored silica skeleton. The alga in green is present in clean environments, while the orange one lives in more polluted water. (Credits: Laure Apothéloz-Perret-Gentil, UNIGE)
