Biomass production and physiology of Chlorella vulgaris during the early stages of immobilized state are affected by light intensity and inoculum cell density

Abstract

The interest for biofilm-based systems for microalgae and related compounds production has been increasing lately. Although extensive literature has been reported on productivity, the physiological characterization (photosynthetic activity and composition) of attached cells at early stages of biofilm development has seldom been investigated. In this work, the effect of light intensity and inoculum cell density on 3-days Chlorella vulgaris biofilms developed on membranes was studied. Biomass production was clearly impacted by mechanism of photo-limitation occurring in biofilms acclimated to low light intensity (50 µmol m -2 s -1 ). A higher electron transport capacity and lower chlorophyll content in biofilms at high light intensity (500 µmol m -2 s -1 ) were also measured which are in line with patterns observed for suspended microalgae cultures. In addition, optimal conditions in terms of light (250 µmol m -2 s -1 ) combined with low (4.8 ×10 6 cells cm -2 ) or high inoculum density (28.8 ×10 6 cells cm -2 ) were identified to optimize biomass and lipids production, respectively. On the whole, measuring physiological profiles of immobilized cells at the initial stages of biofilm development provides information to efficiently operate and optimize biofilm-based systems.

Understanding Chlorella vulgaris acclimation strategies on textile supports can improve the operation of biofilm-based systems

“…5). It is not surprising that on both fabrics (polyamide and cotton-based) biomass increase was inhibited at high initial cell density, indeed a decrease in light and/or nutrients availability in bio lms due to strong selfshading in densely packed populations may occur as already reported in other works (Roberts et al 2004;Huang et al 2016;Roostaei et al 2018;Li et al 2021). On the other hand, C. vulgaris presented 3.2 times higher productivity on the polyamide-based fabric regardless of the initial cell density.…”

“…Photosynthetic activity of immobilized C. vulgaris was assessed using a Pulse Amplitude Modulation (PAM) uorometer (AquaPen, AP 110-C, Photon Systems Instruments, Drasov, Czech Republic). After 10 min of dark-adaptation, the relative electron transport rates (rETRs) corresponding to seven increasing actinic lights were used to construct the rapid light curve (RLC) as described in(Li et al 2021). The maximum rETR (rETR max ) was obtained from the RLC tting function(Webb et al 1974):…”

The architecture and metabolic traits of monospecific photosynthetic biofilms studied in a custom flow‐through system

“…The combination of a constant F v / F m and the decrease in rETR max in C. closterium suggests that photosynthetic capacity could have been limited by dissolved inorganic carbon rather than nutrients such as N and P. Forster and Martin‐Jézéquel (2005) came to similar conclusions for diatoms biofilms grown under dynamic conditions. Furthermore, since on Day 4, the attenuation of light by the biofilms reached 60% of the incident light, the decrease in rETR max and the parallel increase in α could also be indicative of an acclimation of the biofilms to lower PFDs (Dubinsky & Stambler, 2009; Li et al, 2021). This interpretation would also fit with the progressive decrease of the Abs 435 to Abs 676 ratio over time ( p < 0.05; Figure 5a,b) which is a typical response of cells growing at lower light intensities (Dubinsky et al, 1986; SooHoo et al, 1986).…”

“…The photosynthetic efficiency of the biofilms was determined using a portable PAM fluorometer (AquaPen, AP 110-C; Photon Systems Instruments) as described in Li et al (2021). Briefly, the measurements were performed by placing the face of the cuvette colonized by the biofilms in contact with the blue LED (455 nm) of the instrument, the measuring light was 0.02 µmol m −2 s −1 and saturation pulses had an intensity of 3000 µmol m −2 s −1 .…”

Decreased Salinity Offsets the Stimulation of Elevated pCO2 on Photosynthesis and Synergistically Inhibits the Growth of Juvenile Sporophyte of Saccharina japonica (Laminariaceae, Phaeophyta)

“…The alga was also found to downregulate the light utilization efficiency, as shown by the compromised F v /F m and the initial slope (α) of RLC ( Figure 4 ). These reductions seem to be protective strategies that avoid the photo-damage of excess energy to the photosystems and improve the algal capabilities to resist or acclimate to the adverse factors [ 48 , 54 , 55 ]. The elevated pCO 2 decreased the pigments, and the reduction was aggregated by the low salinities.…”