Enhanced growth, chlorophyll a and phycobiliprotein content, and modulation of bioactive metabolite profiles in Synechocystis sp. PCC 6803 culture by ( +)-usnic acid

Synechocystis 6803 is a strain of unicellular freshwater cyanobacteria that can grow in both phototrophic and mixotrophic conditions. We investigated the effects of exogenous ( +)-usnic acid (0.01, 0.1, and 1 µM) on the growth, photosynthetic pigments, and metabolic profiles of Synechocystis 6803 culture through gas chromatography–mass spectrometry analysis (GC–MS) coupled with multivariate statistical analysis. Treatment with 1 µM ( +)-usnic acid enhanced the cell growth at day 14 and the photosynthetic pigments and relative levels (intensity g −1 ) of various bioactive metabolites such as glycine, serine, palmitoleic acid, α-linolenic acid, linoleic acid, oleic acid, stearic acid, 1-monopalmitin, glycerol monostearate, neophytadiene, and α-tocopherol at days 8 and 14. Moreover, enhanced productivity of α-tocopherol was achieved on days 8 (0.36 ± 0.03 mg L −1 or 348 ± 28 μg g −1 ) and 14 (0.47 ± 0.05 mg L −1 or 457 ± 52 μg g −1 ) when treated with 1 µM usnic acid. These results suggest that Synechocystis 6803 can be treated with ( +)-usnic acid to enhance applications in foods, cosmetics, and pharmaceutical industries.