Isoprene Emission in Darkness by a Facultative Heterotrophic Green Alga

K G Srikanta Dani; Giuseppe Torzillo; Marco Michelozzi; Rita Baraldi; Francesco Loreto

doi:10.3389/fpls.2020.598786

Isoprene Emission in Darkness by a Facultative Heterotrophic Green Alga

Front Plant Sci. 2020 Nov 11:11:598786. doi: 10.3389/fpls.2020.598786. eCollection 2020.

Authors

K G Srikanta Dani^{1

2}, Giuseppe Torzillo³, Marco Michelozzi⁴, Rita Baraldi⁵, Francesco Loreto^{2

6}

Affiliations

¹ Institute for Sustainable Plant Protection, National Research Council of Italy, Florence, Italy.
² Department of Biology, Agriculture and Food Sciences, National Research Council of Italy, Rome, Italy.
³ Institute of Bioeconomy, National Research Council of Italy, Florence, Italy.
⁴ Institute for Biosciences and Bioresources, National Research Council of Italy, Florence, Italy.
⁵ Institute of Bioeconomy, National Research Council of Italy, Bologna, Italy.
⁶ Department of Biology, University Federico II, Naples, Italy.

Abstract

Isoprene is a highly reactive biogenic volatile hydrocarbon that strongly influences atmospheric oxidation chemistry and secondary organic aerosol budget. Many phytoplanktons emit isoprene like terrestrial pants. Planktonic isoprene emission is stimulated by light and heat and is seemingly dependent on photosynthesis, as in higher plants. However, prominent isoprene-emitting phytoplanktons are known to survive also as mixotrophs and heterotrophs. Chlorella vulgaris strain G-120, a unicellular green alga capable of both photoautotrophic and heterotrophic growth, was examined for isoprene emission using GC-MS and real-time PTR-MS in light (+CO₂) and in darkness (+glucose). Chlorella emitted isoprene at the same rate both as a photoautotroph under light, and as an exclusive heterotroph while feeding on exogenous glucose in complete darkness. By implication, isoprene synthesis in eukaryotic phytoplankton can be fully supported by glycolytic pathways in absence of photosynthesis, which is not the case in higher plants. Isoprene emission by chlorophyll-depleted mixotrophs and heterotrophs in darkness serves unknown functions and may contribute to anomalies in oceanic isoprene estimates.

Keywords: Chlorella vulgaris; chlorophyll; glycolysis; heterotrophy; marine isoprene; photosynthesis in unicellular eukaryotes; volatile hydrocarbons.