Efficient Green Light Acclimation of the Green Algae Picochlorum sp. Triggering Geranylgeranylated Chlorophylls

Michael Paper; Matthias Glemser; Martina Haack; Jan Lorenzen; Norbert Mehlmer; Tobias Fuchs; Gerhard Schenk; Daniel Garbe; Dirk Weuster-Botz; Wolfgang Eisenreich; Michael Lakatos; Thomas B Brück

doi:10.3389/fbioe.2022.885977

Efficient Green Light Acclimation of the Green Algae Picochlorum sp. Triggering Geranylgeranylated Chlorophylls

Front Bioeng Biotechnol. 2022 Apr 28:10:885977. doi: 10.3389/fbioe.2022.885977. eCollection 2022.

Authors

Michael Paper¹, Matthias Glemser^{1

2}, Martina Haack¹, Jan Lorenzen¹, Norbert Mehlmer¹, Tobias Fuchs^{1

2}, Gerhard Schenk^{3

4}, Daniel Garbe^{1

2}, Dirk Weuster-Botz^{5

2}, Wolfgang Eisenreich⁶, Michael Lakatos⁷, Thomas B Brück^{1

2}

Affiliations

¹ Werner Siemens-Chair of Synthetic Biotechnology, Department of Chemistry, Technical University of Munich, Garching, Germany.
² TUM AlgaeTec Center, Ludwig Bölkow Campus, Department of Aerospace and Geodesy, Taufkirchen, Germany.
³ School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia.
⁴ Sustainable Minerals Institute, The University of Queensland, Brisbane, QLD, Australia.
⁵ Institute of Biochemical Engineering, Faculty of Mechanical Engineering, Technical University of Munich, Garching, Germany.
⁶ Chair of Biochemistry, Department of Chemistry, Technical University of Munich, Garching, Germany.
⁷ Integrative Biotechnology, University of Applied Sciences Kaiserslautern, Pirmasens, Germany.

Abstract

In analogy to higher plants, eukaryotic microalgae are thought to be incapable of utilizing green light for growth, due to the "green gap" in the absorbance profiles of their photosynthetic pigments. This study demonstrates, that the marine chlorophyte Picochlorum sp. is able to grow efficiently under green light emitting diode (LED) illumination. Picochlorum sp. growth and pigment profiles under blue, red, green and white LED illumination (light intensity: 50-200 μmol m^-2 s^-1) in bottom-lightened shake flask cultures were evaluated. Green light-treated cultures showed a prolonged initial growth lag phase of one to 2 days, which was subsequently compensated to obtain comparable biomass yields to red and white light controls (approx. 0.8 g_DW L^-1). Interestingly, growth and final biomass yields of the green light-treated sample were higher than under blue light with equivalent illumination energies. Further, pigment analysis indicated, that during green light illumination, Picochlorum sp. formed unknown pigments (X1-X4). Pigment concentrations increased with illumination intensity and were most abundant during the exponential growth phase. Mass spectrometry and nuclear magnetic resonance data indicated, that pigments X1-X2 and X3-X4 are derivatives of chlorophyll b and a, which harbor C=C bonds in the phytol side chain similar to geranylgeranylated chlorophylls. Thus, for the first time, the natural accumulation of large pools (approx. 12 mg g_DW ^-1) of chlorophyll intermediates with incomplete hydrogenation of their phytyl chains is demonstrated for algae under monochromatic green light (Peak λ 510 nm, full width at half maximum 91 nm). The ability to utilize green light offers competitive advantages for enhancing biomass production, particularly under conditions of dense cultures, long light pathways and high light intensity. Green light acclimation for an eukaryotic microalgae in conjunction with the formation of new aberrant geranylgeranylated chlorophylls and high efficiency of growth rates are novel for eukaryotic microalgae. Illumination with green light could enhance productivity in industrial processes and trigger the formation of new metabolites-thus, underlying mechanisms require further investigation.

Keywords: chlorophyll derivatives; eukaryotic microalgae; geranylgeranylated; green light; light adaption mechanism; photosynthesis.