Light acclimation and pH perturbations affect photosynthetic performance in Chlorella mass culture

Abstract

Chlorella spp. are robust chlorophyte microalgal species frequently used in mass culture. The pH optimum for growth is close to neutrality; at this pH, theoretically little energy is required to maintain homeostasis. In the present study, we grew Chlorella fusca cells in an open, outdoor, thin-layer cascade photobioreactor (TLC), under ambient photon flux at the theoretically preferred pH (7.2), and let the culture pass the exponential growth phase. Using pH drift experiments, we show that an alkalization to pH 9 supported photosynthesis in the TLC. The increased photosynthetic activity under alkaline conditions was a pH-dependent effect, and not a dissolved inorganic carbon (DIC) concentration-or light intensity-dependent effect. Re-acidification (in one step or in increments) lowered gross oxygen production and increased non-photochemical quenching in short-term experiments. Gross oxygen production and electron transport rates in PSII were uncoupled during the pH perturbation experiments. Electron transport rates were only marginally affected by pH, whereas oxygen production rates decreased with acidification. Alternative electron pathways, electron donation at the plastid terminal oxidase and state-transitions are discussed as a potential explanation. Because cell material from the TLC was not operating at maximal capacity, we propose that alkalization can support photosynthesis in challenged TLC systems.

Ammonium Nitrogen Tolerant Chlorella Strain Screening and Its Damaging Effects on Photosynthesis

“…However, these values rapidly decreased to ~pH 3 on the fourth day of culture and stabilized with increasing culture time (Figure 3), which is consistent with the time of growth inhibition for most Chlorella strains (Figure 1). In acidic environment, many enzymes become inactive (Williams and Colman, 1996) and gross oxygen production was lowered (Ihnken et al, 2014) in Chlorella . Therefore, we speculated that the growth inhibition in the middle and late stages was due to acidification of the medium.…”

Bioremediation by Chlorella vulgaris: Potentials for Treatment of Municipal, Agricultural, and Industrial Wastewater Sources

“…It has a pivotal role in determining the biological activity and solubility of chemical constituents in wastewater treatment processes, as metals become more toxic at lower pH in a way that the toxic compounds bind with other ions (Akcin et al, 2006;Brandt et al, 2017). Therefore, the proposed pH value in wastewater required for microalgal growth is 6.5 to 7.0, or those close to neutrality (Ihnken et al, 2014;Wang et al, 2015). Microalgae induce an increase in the pH of the media as they photosynthesize (Larsdotter, 2006).…”

“…Chlorella vulgaris grows best at an initial pH of 6.5 to 7.0, or those close to neutrality since relatively little energy is required to maintain homeostasis (Ihnken et al, 2014;Wang et al, 2015). Regardless, Goldman et al (1982), as cited in Ihnken et al (2014), stated that Chlorella can grow efficiently up to a pH of 10.5. This increasing pH is due to the photosynthetic CO2 assimilation of the microalgae (Ramanan et al, 2016).…”

Cultivation of microalgae at high-density with pretreated liquid digestate as a nitrogen source: Fate of nitrogen and improvements on growth limitations

“…Despite the addition of NaOH, pH fluctuated daily, yet this was due to the CO 2 injection that was switched off during the night. C. vulgaris is tolerant to the basification of the growth medium (Ihnken et al, 2014), which also has the benefit of decreasing the risk of biological contamination (Wang et al, 2013). While the PLD…”