Microalgae cross-fertilization: short-term effects of Galdieria phlegrea extract on growth, photosynthesis and enzyme activity of Chlorella sorokiniana cells

Galdieria spp. (Rhodophyta) are polyextremophile microalgae known for their important antioxidant properties in different biological systems. Nowadays, the beneficial and bio-stimulant effect of microalgal extracts is widely tested on crops. Here, for the first time, potential positive effects of aqueous extracts from Galdieria were tested on a second microalgal culture systems. Chlorella sorokiniana cultures were supplemented with Galdieria phlegrea extracts (EC) and the short-term (48 h) effects of extract addition on growth and biochemical and physiological parameters were monitored and compared to those of non-supplemented Chlorella (CC). Growth of Chlorella was improved in EC as shown by higher optical density and cells number in the enriched cultures. In addition, EC appreciably increased the pigments (chlorophyll (a and b) and carotenoids) contents of Chlorella cells. Increase of photosynthetic pigments was associated with higher photosynthesis and lower non-radiative dissipation of light in EC as indicated by chlorophyll fluorescence parameters. Reduced activities of antioxidant enzymes (SOD, CAT and APX), but increased total antioxidant capacity (ABTS) were observed in EC, suggesting that this culture was under a low oxidative status, but can activate antioxidant defences if exposed to oxidative stress. In conclusion, a short-term positive effect of the addition of G. phlegrea extracts on growth and physiology of C. sorokiniana was demonstrated.