77K Chl a fluorescence emission spectra
77K emission spectra of whole cells of the mesophilic SAG 49.72
exhibited prominent fluorescence peaks at 684 nm and 714-716 nm
consistent with LHCII-PSII and PSI fluorescence emission, respectively
(Figure 3a). In contrast with the mesophile, UWO 241 exhibited major Chl
a fluorescence emission peaks at 685 nm and 697 nm, but lacked a
prominent emission peak for PSI at longer wavelengths 715-720 nm (Figure
3b). Acclimation to long-term stress resulted in changes in the 77K Chl
a fluorescence emission spectra of SAG 49.72 (Figure 3a). Gaussian
analysis of the fluorescence spectra revealed that SAG 49.72 exhibited a
1.5- to 3.2-fold decrease in the ratio of PSII/PSI fluorescence in
response to LT, HL or HS stress (Table S1). In contrast, UWO 241 cells
exhibited minimal changes in PSI fluorescence (Figure 3b), and only HS
stress resulted in a minor decrease (1.18-fold relative to control) in
the PSII/PSI ratio of UWO 241 (Table S1).