Growth, photosynthesis, and respiration of Chlorella sorokiniana after N‐starvation. Interactions between light, CO₂ and NH₄⁺ supply

Abstract

N‐sufficient cells of Chlorella sorokiniana Shihira and Krauss, strain 211/8k, absorbed NH4+ under light plus CO2 conditions, when growth occurred, but not in darkness or in the absence of CO2, when growth was inhibited. N‐sufficient cells subjected to conditions of N‐starvation for a 24‐h period showed a marked loss of photosynthetic activity. Upon supply of NH4+, N‐starved cells sufflated with CO2 air exhibited a time‐dependent recovery of photosynthetic activity, both when suspended in light and in darkness. By contrast, growth only occurred in cells suspended in light. N‐starved cells absorbed NH4+ in darkness, but at a lower rate than in light. All of these data suggest that dark NH4+ uptake is driven by N assimilation to recover from N‐starvation and that the light‐dependent NH4+ uptake is driven by growth, being then influenced by conditions that affect recovery or growth. Unlike CO2 conditions, in a CO2‐free atmosphere, absorption of NH4+ by N‐starved cells occurred at a higher rate in darkness than in light. Accordingly, resumption of photosynthetic potential after NH4+ supply occurred in darkened cells, but not in illuminated cells. Respiratory activity of N‐starved cells was enhanced up to 3‐fold by NH4+ and 2‐fold by methylammonium, with different patterns, suggesting that respiratory enzymes were affected by N‐metabolism, especially through short‐term control mechanisms triggered by the expenditure of metabolic energy involved in N‐metabolism.

Cross-Effects of Nitrogen and Sulphur Starvation in <i>Chlorella sorokiniana</i> 211/8K

“…As previously reported, chlorophyll content strongly decreased upon both S-and N-starvation [3] [22]. Several studies indicate the degradation of PSII as responsible for this decrease [23].…”

“…+ or 3 NO − transport systems [3] [4]. In addition, in the process of acclimation to long term N-deficiency, microalgae have been reported to degrade ribosomes and decrease enzyme activities involved in gluconeogenesis and photosynthetic carbon fixation cycle [1].…”

“…The composition of the basal medium was previously reported [10]. S-and N-starved cells were obtained collecting batch grown cells by a low speed centrifugation (4000 r for 5 min), washed two times and re-suspended in a N-free or S-free medium as previously described [3] [11]. Algal growth was evaluated by absorbance (OD 550 ).…”

Scenario Analysis of Nutrient Removal from Municipal Wastewater by Microalgal Biofilms

“…N-limited microalgae, on the other hand, are known to take up either NO 3 − or NH 4 + in the dark. Uptake of NH 4 + can be more than 50% of the daylight value in N-limited microalgae [30]. Consequently, when N is the limiting nutrient for microalgae in the treatment of municipal wastewater, considerable uptake of N during darkness might be expected.…”

“…In Scenario 1 these lipids would approximately amount to 79 ton during the five summer months of operation (see Appendix C). However, further research is still needed to induce the accumulation of specific desired lipids, to obtain a stable (mixed) culture of the desired species in the system, and to set up the biorefinery needed to extracts these lipids as well as valorize the remaining biomass constituent [30,31].…”