@article{45f546a486b34836855599ad3a002d85,
title = "A comparison between microalgal autotrophic growth and metabolite accumulation with heterotrophic, mixotrophic and photoheterotrophic cultivation modes",
abstract = "Microalgae are sustainable feedstock for healthy food and feed, organic drugs, ecological polymers, green chemicals and dyes, biofuels, biofertilizers, and environmental bioremediation technologies. Despite its enormous promises, microalgae cultivation is expensive and thus large-scale production is centred on low volume/high value markets, such as the specialty food and feed, dietary supplements and pharmaceuticals. Large-scale microalgal cultivation is severely limited by the low biomass productivity achieved in current production systems, due to low photosynthetic efficiency. Furthermore, the management of carbon dioxide (CO2) for microalgal large-scale production is costly and faces technological constraints. The cultivation of microalgae in media supplemented with organic carbon substrates, with or without light, can significantly increase biomass productivities and overcome the technical constraints associated to CO2 supply. This review collects quantitative data to compare microalgal autotrophic growth and metabolite accumulation with heterotrophic, mixotrophic and photoheterotrophic cultivation modes. Critique hypotheses are proposed to explain the increase in biomass productivity once microalgae are supplied with organic carbon molecules. The main cultivation parameters that could affect biomass accumulation are also analysed. Supplementation of microalgae with organic carbon substrates could be a suitable strategy towards a microalgal economy, despite the constraints and challenges that have to be overcome and that are also analysed.",
keywords = "Autotrophic, Bioeconomy, Heterotrophic, Microalgae, Mixotrophic, Organic carbon, Photoheterotrophic",
author = "Abreu, {Ana P.} and Morais, {Rui C.} and Teixeira, {Jos{\'e} A.} and Jo{\~a}o Nunes",
note = "Funding Information: This work was supported by COMPETE 2020 [3iBioeconomia: POCI-01-0246-FEDER-026758]; Funda{\c c}{\~a}o para a Ci{\^e}ncia e Tecnologia [SFRH/BDE/100385/2014]; and Association BLC3 – Technology and Innovation Campus, Centre Bio R&D Unit (UID/05083/2020). Funding Information: Some studies reported a decline in photosynthesis in the presence of OCS, suggesting that mixotrophic growth is mainly supported by the aerobic oxidation of the reduced molecules. Mixotrophic cultures of P. tricornutum in media supplemented with glycerol, acetate or glucose significantly exhibited higher growth rates (0.14?0.18 d?1) and biomass concentrations (0.55?0.71 g l?1) comparing to autotrophic conditions (0.11 d?1 and 0.46 g l?1), despite the lower photosynthesis efficiency exhibited (decreased net photosynthetic O2 evolution, reduced efficiency of photosystem II (PSII) and diminished content of photosynthetic pigments) [143]. The supplied OCSs significantly increased the respiration rate, thus indicating they had more pronounced effects on respiration than on photosynthesis. Similarly, mixotrophic cultures of C. vulgaris exhibited a growth rate (?mix = 0.034 h?1) higher than autotrophic one (?aut = 0.023 h?1), although the photosynthesis was reduced in the first (reduced chlorophyll content and PSII activity); on the other hand, the glyoxylate cycle exerted an important role in mixotrophy, as in heterotrophic cultures [46]. The photosynthetic yields of PSII from mixotrophic cultures of Chlamydomonas sp., C. vulgaris, and Desmodesmus spinosus were up to 60% lower than in autotrophic ones, but the biomass productivities were significantly higher, suggesting that other pathways were operating in the cells to increase their biomass production [54]. Besides, photochemical quenchings (qP) were similar in both autotrophic and mixotrophic cultures suggesting that PSII was not affected by OCS supplementation and mixotrophic cells kept the capacity to direct light energy to photochemistry. Despite increasing the growth rate, the addition of glucose to the medium severely inhibited the photosynthesis in C. vulgaris cells, due to a reduction in the apparent affinity for extra-cellular CO2 [144].This work was supported by COMPETE 2020 [3iBioeconomia: POCI-01-0246-FEDER-026758]; Funda??o para a Ci?ncia e Tecnologia [SFRH/BDE/100385/2014]; and Association BLC3 ? Technology and Innovation Campus, Centre Bio R&D Unit (UID/05083/2020). Publisher Copyright: {\textcopyright} 2022 Elsevier Ltd",
year = "2022",
month = may,
doi = "10.1016/j.rser.2022.112247",
language = "English",
volume = "159",
journal = "Renewable and Sustainable Energy Reviews",
issn = "1364-0321",
publisher = "Elsevier Ltd.",
}
