Chromatic Adaptation in Cyanobacterium E412

The strain E412 presented in the current study was initially isolated from Lotus Lake hot springs in the Ganzi region of Sichuan Province, China. Information about the sampling site and preliminary taxonomic allocation of the strain was reported in our previous studies (Tang et al., 2018a ,b (link)). The unicyanobacterial culture of the strain was cryopreserved as 10% DMSO in BG11 stocks in −80°C. Final precultures for experiments were established as previously described (Tang et al., 2018b (link)) and cultivated at 45°C in 150 mL BG-11 medium in 500 mL Erlenmeyer flasks agitated at 100 rpm under 12L:12D photoperiod at 45 μmol m^–2 s^–1 provided by fluorescent tubes unless stated otherwise. The strain initially denoted as PKUAC-SCTE412 has been recently deposited in the Freshwater Algae Culture Collection at the Institute of Hydrobiology (FACHB-collection) with an accession number FACHB-2490. Physiological assessment of the strain was performed using BG-11 medium free of an essential nutrient (nitrogen or sulfur) supplemented with 17 mM NaNO₂, 85 mM NaNO₃, 10 mM Na₂SO₄, and 10 mM NaHSO₃. The nitrogen fixation capacity during 72 h was performed using the methodology described by Li et al. (2021) (link).
The chromatic adaptation capacity of strain E412 was assessed by culturing the cells at constant LED illumination using either white light (6,500 K) or far-red light (730 nm) at the intensity of 250 and 25 μmol m^–2 s^–1, respectively. After 15 days, cyanobacterial cells were collected to measure chlorophyll a, chlorophyll b, carotenoids, allophycocyanin, phycocyanin, and phycoerythrin, according to previously published protocols (Bennett and Bogorad, 1973 (link); Dere et al., 1998 ). Lipophilic and water-soluble pigments from 15 mg of lyophilized biomass were extracted with 100% methanol and phosphate-buffered saline (PBS), respectively. The absorbance of the supernatant at 470, 562, 615, 652, 653, and 666 nm were recorded against the relative blank using a UV-Vis spectrophotometer (Shimadzu UV-1,800, Japan). The concentration of pigments was calculated using respective formulae for chlorophylls and carotenoids (Dere et al., 1998 ) and phycobiliproteins (Bennett and Bogorad, 1973 (link)).