Growth and photosynthetic performance of Chlamydopodium fusiforme cells cultivated in BG11 and Bristol media
Nitrogen is an essential nutrient for all life forms and its availability is periodically limited in marine and freshwater ecosystems. To optimize the growth of the freshwater microalga Chlamydopodium fusiforme and to investigate the cell acclimation process to different amounts of nitrogen, we grew cells in Bristol and BG11, under fixed conditions of 10 h:14 h light/dark cycle. Cultures grown in BG11 exhibited higher biomass accumulation, reaching a cell dry weight of 1.94 ± 0.1 g L−1, while in Bristol it reached 1.58 ± 0.1 g L−1. In cells grown in BG11, chlorophyll content increased continuously up to 79.6 mg L−1 (9th day), while in Bristol it was much lower (29.5 mg L−1). This fact caused a strong difference in their spectrally averaged optical cross-section normalized to chlorophyll a (a*), and consequently in their photosynthetic performance (oxygen evolution and electron transport rates). Carotenoid content followed a similar pattern. It was interesting to note that despite this great difference in chlorophyll concentration, both photosynthesis rate and cell dry weight were not affected proportionally. The chlorophyll a fluorescence measurements indicated a stable effective quantum yield of photosystem II in both culture conditions. During the dark phase of the cycle we observed in both cultures a remarkable reduction of both electron transfer and photosynthesis rates, while maximum quantum yield of PSII remained stable (0.74 ± 0.01). This indicated that the reduction in both photosynthesis rate and maximum electron transport rate (ETRmax) observed during the dark phase were not due to damage of PSII reaction centers but rather to reduced flow of electron subsequent to PSII. Recovery of the fully photosynthetic capacity required about 1 h of illumination.
KeywordsChlamydopodium fusiforme Chlorophyceae Microalgae Variable fluorescence Photosynthesis Biomass composition
We thank Dr. Cecilia Faraloni for her technical assistance with the HPLC analysis and Mr. Alessandro Dodero for his technical assistance with the CHNOS elemental analysis. The authors wish to thank Dr. Bernardo Cicchi for the English revision of the manuscript.
The work has been supported by the H2020 project “SABANA” funded from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 727874.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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