Li 250a light meter

Culture growth was monitored by optical density at 660 nm (OD₆₆₀) using a Genesys 20 visible spectrophotometer (Thermo-Fisher). Room temperature absorbance spectra of whole cells resuspended in 60% (wt/vol) sucrose in PM were recorded using a Synergy MX spectrofluorimeter (BioTek). Light intensity was monitored using a LI-250A light meter equipped with a LI-190R quantum sensor (LI-COR).
Bacteriochlorophyll a (BChl-a) was extracted and quantified as previously described (28 (link), 60 (link)). Briefly, cells were centrifuged and resuspended in 600 µl phosphate-buffered saline (PBS), at which point sample OD₆₆₀ was recorded. Cells were then pelleted again, resuspended in 20 µl H₂O, mixed with 1 ml 7:2 (vol/vol) acetone-methanol solvent, and incubated at room temperature in darkness for 90 min. Cell debris was removed by centrifugation (at maximum speed for 5 min), and extracted BChl-a was detected by recording supernatant absorbance at 770 nm (A₇₇₀). BChl-a content is reported normalized to sample optical density (A₇₇₀/OD₆₆₀).

Anaerobic cultures of Rba. sphaeroides grown under photosynthetic conditions were exposed to 15 W or 20 W MEGAMAN® CFL bulbs to achieve the desired light intensity. Light intensity was measured in μmol photons s⁻¹ m² using a LI‐250A light meter equipped with a LI‐190 Quantum sensor (LI‐COR Biosciences). One millilitre of semi‐aerobic culture was used to inoculate a full 30 ml universal of M22+ medium. A small magnetic stir bar was placed in the bottom of the bottle, and the culture was incubated in the desired light intensity, overnight with gentle agitation. This culture was used to inoculate either a 500 ml medical flat or a 1.2 l Roux culture bottle filled with M22+ medium and capped with a rubber bung. These cultures also contained a magnetic stir bar to allow for gentle agitation.

To isolate Nannochloropsis strains, F/2 agar plates were incubated at 25 ℃ under 50 µmol photon m^− 2 s^− 1 light intensity. For strain maintenance and all the other experiments, the cells were cultivated in a 50 mL T-flask (SPL, Pocheon, Republic of Korea) with a working volume of 10 mL at 25 ℃ with agitation of 120 rpm. In the experiments for the comparison of light intensity, the intensity of normal light (NL) and high light (HL) were 50 and 150 µmol photon m^− 2 s^− 1, respectively, and each intensity condition was confirmed using a LI-250A light meter (LI-COR, NE, USA). Large-scale cultivations were carried out in a 10 L cylindrical bioreactor (custom-made) with 5 L working volume. Air was supplied into the culture solution by using a strong air pump with the flow rate of 25 L min^− 1 for the aeration and agitation. At the beginning of the cultivation, a flat light source of 300 µmol photon m^− 2 s^− 1 was used in only one side of the bioreactor. 6 days after inoculation, another light source of 100 µmol photon m^− 2 s^− 1 was introduced in the opposite side to compensate for shading effect.