Phototrophic growth of Arthrospira platensis in a respiration activity monitoring system for shake flasks (RAMOS®)

Abstract

Optimizing illumination is essential for optimizing the growth of phototrophic cells and their production of desired metabolites and/or biomass. This requires appropriate modulation of light and other key inputs and continuous online monitoring of their metabolic activities. Powerful noninvasive systems for cultivating heterotrophic organisms include shake flasks in online monitoring units, but they are rarely used for phototrophs because they lack the appropriate illumination design and necessary illuminatory power. This study presents the design and characterization of a photosynthetic shake flask unit, illuminated from below by warm white light‐emitting diodes with variable light intensities up to 2300 μmol m−2 s−1. The photosynthetic unit was successfully used, in combination with online monitoring of oxygen production, to cultivate Arthrospira platensis. In phototrophic growth under continuous light and a 16 h light/8 h dark cycle (light intensity: 180 μmol m−2 s−1), the oxygen transfer rate and biomass‐related oxygen production were −1.5 mmol L−1 h−1 and 0.18 mmol O2 gx−1 h−1, respectively. The maximum specific growth rate was 0.058 h−1, during the exponential growth phase, after which the biomass concentration reached 0.75 g L−1.

The challenge of scaling up photobioreactors: Modeling and approaches in small scale

“…The RAMOS has primarily been developed for chemo‐organotrophic microbes where the metabolic activity is measured as oxygen consumption and CO 2 production . The here‐shown experiments were performed in a RAMOS with a lighting unit for cultivation of phototrophic microbes . A. platensis PCC 9108 was cultivated in 30 mL Zarrouk medium at permanent illumination with 75–1300 μmol m –2 s –1 , 30°C and shaking with 110 min –1 (0.4 cm medium thickness).…”

“…Low cell densities result in small and fluctuating OER ( t ) signals (the signal‐to‐noise ratio is too small) while high cell densities generate large OER ( t ) signals but cause self‐shading. Moreover, orbital shaking results in a nonuniform Δ x value, the CultiLux unit emits a somewhat heterogeneous light field , sampling is impossible, and using averaged light intensities for the μ ( I ) graph conflicts with the favored concept, i.e., the RAMOS‐CultiLux system is less suited for studying the growth kinetics.…”

“…Another calculation mode is based on Eq. in where C X ( t ) is substituted with the above‐given equation resulting in μ ( t ) = OTR ( t )/( C X ( t = 0)· + OE ( t )).…”

“…The OER(t) data were used to calculate specific growth rates assuming a strict correlation of oxygen production and microbial growth. Other than Socher et al [26], who calculated μ(t) from OER(t) and C X (t) data (the latter measured in parallel flasks), an upgraded mode of data exploration is used here which allows μ(t) calculations independently of measured cell densities. The accumulative oxygen evolution OE(t) was obtained from the OER(t) data by Eq.…”

Editorial: Plant cells and algae in bioreactors

“…Kula et al further provide evidence for the influence of far‐red light on biomass production of Chlorella vulgaris . An innovative study of cultivation of cells under illumination is presented by Socher et al . The authors outline the perspectives of a RAMOS cultivation system for investigating the growth of phototrophic organisms under controlled light conditions .…”