Improvement of In Vivo Fluorescence Tools for Fast Monitoring of Freshwater Phytoplankton and Potentially Harmful Cyanobacteria.

The use of multi-wavelength spectrofluorometers for the fast detection of algal taxa, based on chlorophyll a (Chl-a) emission spectra, has become a common practice in freshwater water management, although concerns about their accuracy have been raised. Here, inter-laboratory comparisons using monoalgal cultures have been performed to assess the reliability of different spectrofluorometer models, alongside Chl-a extraction methods. Higher Chl-a concentrations were obtained when using the spectrofluorometers than extraction methods, likely due to the poor extraction efficiencies of solvents, highlighting that traditional extraction methods could underestimate algal or cyanobacterial biomass. Spectrofluorometers correctly assigned species to the respective taxonomic group, with low and constant percent attribution errors (Chlorophyta and Euglenophyceae 6-8%, Cyanobacteria 0-3%, and Bacillariophyta 10-16%), suggesting that functioning limitations can be overcome by spectrofluorometer re-calibration with fresh cultures. The monitoring of a natural phytoplankton assemblage dominated by Chlorophyta and Cyanobacteria gave consistent results among spectrofluorometers and with microscopic observations, especially when cell biovolume rather than cell density was considered. In conclusion, multi-wavelength spectrofluorometers were confirmed as valid tools for freshwater monitoring, whereas a major focus on intercalibration procedures is encouraged to improve their reliability and broaden their use as fast monitoring tools to prevent environmental and public health issues related to the presence of harmful cyanobacteria.

Production of polyhydroxybutyrate by the cyanobacterium cf. Anabaena sp.

Polyhydroxybutyrate (PHB) production by the cyanobacterium cf. Anabaena sp. was here studied by varying the medium composition and the carbon source used to induce mixotrophic growth conditions. The highest PHB productivity (0.06 gPHB gbiomass-1 d-1) was observed when cultivating cf. Anabaena sp. in phosphorus-free medium and in the presence of sodium acetate (5.0 g L-1 concentration), after an incubation period of 7 days. A content of 40% of PHB on biomass, a dry weight of 0.1 g L-1, and a photosynthetic efficiency equal to the control were obtained. The cyanobacterium was then grown on a larger scale (10 L) to evaluate the characteristics of the produced PHB in relation to the main composition of the biomass (the content of proteins, polysaccharides, and lipids): after an incubation period of 7 days, a content of 6% of lipids (52% of which as unsaturated fatty acids with 18 carbon atoms), 12% of polysaccharides, 28% of proteins, and 46% of PHB was reached. The extracted PHB had a molecular weight of 3 MDa and a PDI of 1.7. These promising results demonstrated that cf. Anabaena sp. can be included among the Cyanobacteria species able to produce polyhydroxyalkanoates (PHAs) either in photoautotrophic or mixotrophic conditions, especially when it is grown under phosphorus-free conditions.

Use of waste carbon dioxide and pre-treated liquid digestate from biogas process for Phaeodactylum tricornutum cultivation in photobioreactors and open ponds.

Phaeodactylum tricornutum is considered a promising source of polyunsaturated fatty acids (PUFAs), in particular eicosapentaenoic acid (EPA). In this study, P. tricornutum cultivation using waste products from anaerobic digestion (i.e. liquid digestate and CO2) was tested and scaled-up in closed and open prototype systems. The chemical composition of algal biomass was evaluated to optimize the lipid content. Algal productivity and composition, especially in terms of PUFAs, were not modified by the use of waste CO2. Digestate led to a lower protein (24%) content than medium (36-37%), without affecting lipid amount (about 37%). Algal and EPA productivity were nearly two-fold higher by using photobioreactors (0.075 g biomass L-1 day-1 and 1.62 mg EPA g-1 day-1) than open ponds, which are more influenced by environmental conditions. This study highlights that economic and environmental benefits could be achieved by using waste CO2 and liquid digestate from anaerobic digestion for microalgae cultivation.