Effect of Different Broad Waveband Lights on Membrane Lipids of a Cyanobacterium, Synechococcus sp., as Determined by UPLC-QToF-MS and Vibrational Spectroscopy

Abstract

Differential profile of membrane lipids and pigments of a Synechococcus sp. cyanobacterial strain cells exposed to blue, green, red and white light are determined by means of liquid chromatography and mass spectrometry or diode array detection. Raman and ATR-IR spectra of intact cells under the diverse light wavebands are also reported. Blue light cells exhibited an increased content of photosynthetic pigments as well as specific species of membrane glycerolipids as compared to cells exposed to other wavebands. The A630/A680 ratio indicated an increased content of phycobilisomes (PBS) in the blue light-exposed cells. Some differences in the protein conformation between the four light waveband-exposed cells were deduced from the variable absorbance at specific wavenumbers in the FT-Raman and ATR-FTIR spectra, in particular bands assigned to amide I and amide II. Bands from 1180 to 950 cm(-1) in the ATR-FTIR spectrum suggest degraded outer membrane polysaccharide in the blue light-exposed cells.

Keywords: IR; Raman; Synechococcus sp.; UPLC-MS; light quality; lipids; pigments; vibrational spectroscopy.

Figure 1

Typical base peak intensity (BPI) chromatograms obtained for the methanolic extract after UPLC-MS analysis of the culture covered with a blue filter for 24 h (upper panel), the culture covered with a red filter for 24 h (second panel down from top), the culture covered with a transparent filter for 24 h (second panel up from bottom), and the stock culture grown under white light and used for the inoculum of the transparent, red and blue filter cultures (lower panel). The numbers above each chromatographic peak indicates the retention time (up) and the m/z predominating in that peak (down). Right legends: 1. TOF MS ES+, MS with electrospray positive ionization; BPI, base peak intensity; number, intensity to which 100% is fitted.

Figure 2

Relative content normalized to the absorbance at 750 nm of the monogalactosyldiaylglycerol (MGDG) species, digalactosyldiacylglycerol (DGDG) species, sulfoquinovosyldiacylglycerol (SQDG) species, and phosphatidyldiacylglycerol (PG) species as measured by UPLC-MS with positive (MGDG and DGDG) or negative (SQDG and PG) electrospray ionization from a methanolic extract of Synechococcus sp. cells. Glycerolipid nomenclature used in this study is that recommended by the LipidMaps consortium (http://www.lipidmaps.org/), where the acyl chains esterifying the sn-1 and the sn-2 positions of the glycerol backbone are located in the first and second places within the brackets (sn-1/sn-2), and the polar head group (phosphatidylglycerol, sulfoquinovosyl, galactosyl and digalactosy) is assumed to esterify the sn-3 position of the glycerol backbone.

Figure 2

Relative content normalized to the absorbance at 750 nm of the monogalactosyldiaylglycerol (MGDG) species, digalactosyldiacylglycerol (DGDG) species, sulfoquinovosyldiacylglycerol (SQDG) species, and phosphatidyldiacylglycerol (PG) species as measured by UPLC-MS with positive (MGDG and DGDG) or negative (SQDG and PG) electrospray ionization from a methanolic extract of Synechococcus sp. cells. Glycerolipid nomenclature used in this study is that recommended by the LipidMaps consortium (http://www.lipidmaps.org/), where the acyl chains esterifying the sn-1 and the sn-2 positions of the glycerol backbone are located in the first and second places within the brackets (sn-1/sn-2), and the polar head group (phosphatidylglycerol, sulfoquinovosyl, galactosyl and digalactosy) is assumed to esterify the sn-3 position of the glycerol backbone.

Figure 3

Relative content normalized to the absorbance at 750 nm of the main photosynthetic pigments as measured by HPLC-DAD from a methanolic extract of Synechococcus sp. cells. Legend: W, transparent filter; B, blue filter; G, green filter; and R, red filter. X-axes legend: Myx, myxoxanthophyll; Zeax, zeaxanthin; HO-echin, hydroxy-echinenone; Unk, unknown (echinenone related); Chl a, chlorophyll a; b-car, β-carotene.

Figure 4

Raman spectra of intact Synechococcus sp. cells exposed to blue (B), green (G), red (R) and white (W) light.

Figure 5

Attenuated reflectance Fourier-Transformed Infrared spectra (ATR-FTIR) of intact Synechococcus sp. cells exposed to blue (B), green (G), red (R) and white (W) light.