Influence of nutrient status on the biohydrogen and lipid productivity in Parachlorella kessleri: a biorefinery approach

The commercial reality of microalgal biotechnology for the production of individual bioactives is constrained by the high cost of production and requires a biorefinery approach. In this investigation, we examined the influence of different nutrient deprivation (nitrogen (N), phosphorus (P), sulphur (S) and manganese (Mn)) on growth, chlorophyll a (Chl a), biohydrogen (H₂) and fatty acid profiles in Parachlorella kessleri EMCCN 3073 under both aerobic and anaerobic conditions. Anaerobic conditions combined with the nutrient deprivation resulted in cell division blockage, reduction in Chl a and remarkable changes in pH, whereas a significant increase in the H₂ production was observed after 24 h. The highest cumulative H₂ productivity was observed in N-deficient medium (300 μL/L, day 9) followed by Mn-deficient medium (250 μL/L, day 7). The highest H₂ production rate (3.37 μL/L/h) was achieved by Mn-deficient medium after 24 h. In terms of fatty acid composition, P. kessleri exhibited a differential response to different nutrient stresses. Under aerobic conditions, N-deficient media resulted in the highest lipid content (119% compared to control, day 7), whereas earlier lipid induction at (1–3 days) was observed with Mn- and S-deficient media with 18–91% and 25–34% increase, respectively, compared with the replete control. Meanwhile, higher lipid content was observed under anaerobic conditions combined with Mn-, N-, P- and S-deprived media (day 1) with 20%, 13%, 8% and 7% increases respectively compared with the control. This investigation, for the first time clearly, highlights the potential of P. kessleri as a sustainable biorefinery platform, for H₂ and fatty acid bio-production under anaerobic conditions. KEY POINTS: • Parachlorella kessleri could provide a future sustainable biorefinery platform. • Nutrient-deprived anaerobic conditions blocked cell growth but differentially induced H₂ production. • Nutrient status, under both aerobic/anaerobic conditions, alters lipids and fatty acids profile of P. kessleri. • Nutrient-deprived (N- and Mn-) anaerobic conditions: future biorefinery platform.