Dynamics of long‐term continuous culture of Limnospira indica in an air‐lift photobioreactor

Abstract

MELiSSA (Microecological Life Support SystemAlternative) is a developing technology for regenerative life support to enable long-term human missions in Space and has developed a demonstration Pilot Plant. One of the components of the MELiSSA Pilot Plant system is an 83L external loop air-lift photobioreactor (PBR) where Limnospira indica (previously named Arthrospira sp. PC8005) is axenically cultivated in a continuous operation mode for longperiods. Its mission is to provide O 2 and consume CO 2 while producing edible material. Biological and process characterization of this PBR is performed by analysing the effect of two main variables, dilution rate (D) and PFD (Photon Flux Density) illumination. A maximum oxygen productivity (r O 2 ) of 1.35 mmol l −1 h −1 is obtained at a D of 0.025 h −1 and PFD of 930 µmol m −2 s −1 . Photoinhibition can occur when a 1 g l −1 cell density culture is exposed to PFD higher than 1700 µmol m −2 s −1 . This process is reversible if the illumination is returned to dim light (150 µmol m −2 s −1 ), proving the cell adaptability and capacity to respond at different illumination conditions. Influence of light intensity in cell composition is also described. Specific photon flux density (qPFD) has a direct effect on phycobiliproteins and chlorophyll content causing a decrease of 62.5% and 47.8%, respectively, when qPFD increases from 6.1 to 19.2 µmol g −1 s −1 . The same trend is observed for proteins and the opposite for carbohydrate content. Morphological and spiral structural features of L. indica are studied by confocal microscopy, and size distribution parameters are quantified. A direct effect between trichome width and CDW/OD ratio is observed. Changes in size distribution are not correlated with environmental factors, further confirms the adaptation capacity of the cells. The systematic analysis performed provides valuable insights to understand the key performance criteria of continuous culture in air-lift PBRs.

Assessment of batch culture conditions for cyanobacterial propagation for a bioreactor in space

“…Deamici et al (2022) obtained a chlorophyll content of 1.11 ± 0.15 mg g DW -1 (~0.001 g g DW -1 , in L. indica PCC8005) which is much lower than the values presented in this study. Garcia-Gragera et al (2021) found a phycobilliprotein content between 0.037 and 0.125 g g DW -1 and a chlorophyll content between 0.007 and 0.018 g g DW -1 (also in L. indica PCC8005), which is very similar to our results (0.018 and 0.130 g g DW -1 for phycocyanin and 0.004-0.024 g g DW -1 for chlorophyll). Karemore et al (2020) confirmed that the temperature does not only play a role in the general biomass production but also impacts the pigment content in a semi-continuous PBR culture of A. platensis.…”

“…It is important to keep in mind that several factors influence the light conditions inside a culture. For example, a high biomass density in a culture causes shading effects which impact the light availability and therefore also the biomass production (Poughon et al, 2020;Garcia-Gragera et al, 2021;Chaiklahan et al, 2022), therefore not only the light intensity but also the availability of light plays an important role. Additionally, the wavelength composition of the light influences the performance of a cyanobacterial culture.…”

“…Therefore, depending on the experimental set-up, varying biomass and oxygen productivities are reported in literature. For example, Farges et al (2009) reported a biomass productivity of 0.077 g L -1 d -1 for 33 µmol photons m -2 s -1 in an 1.2 L bench scale membrane bioreactor; while Garcia-Gragera et al (2021) obtained already a maximum biomass productivity of 0.58 g L -1 d -1 for 932 µmol photons m -2 s -1 and a maximum oxygen productivity of 1.19 mmol L -1 h -1 in the larger intensified 90 L cylindrical airlift bioreactor at the MELiSSA pilot plant in Barcelona. In the ArtEMISS project, mini-sized PBRs which are adapted to spaceflight conditions are used.…”

“…It is known that temperature and light conditions have an impact on revival and oxygen and biomass production kinetics and biomass composition (Moore et al, 1995;Ravelonandro et al, 2008;Garcia-Gragera et al, 2021). Our study focusses on conditions relevant for PBR systems for space applications like moderate temperatures between 21 °C and 34 °C and low light intensities (i.e.…”