A new approach for detection and quantification of microalgae in industrial-scale microalgal cultures

In industrial-scale microalgal cultures, non-target microalgae compete with the desired species for nutrients and CO₂, thus reducing the growth rate of the target species and the quality of the produced biomass. Microalgae identification is generally considered a complicated issue; although, in the last few years, new molecular methods have helped to rectify this problem. Among the different techniques available, DNA barcoding has proven very useful in providing rapid, accurate, and automatable species identification; in this work, it is used to assess the genomic identity of the microalga species Scenedesmus sp. 'almeriensis', a common strain in industrial-scale cultures. Barcode markers rbcL and ITS1-5.8S-ITS2 were sequenced and the obtained genomic information was used to design a quantitative PCR assay to precisely quantify the S. almeriensis concentration in microalgal cultures of industrial interest. TaqMan chemistry was used to quantify down to 1 μg/L dry weight of S. almeriensis cells, including in the presence of concentrated mixed cultures of other microalgae. A simple direct qPCR approach was also investigated to avoid classic DNA extraction and to reduce total assay time to approximately 2 h. The objective was to design strain-specific tools able to confirm and quantify the presence of different strains in whatever microalgae culture so as to achieve maximal productivity and quality of the produced biomass.