The metabolome of Chlamydomonas reinhardtii following induction of anaerobic H2 production by sulfur depletion.

Abstract

The metabolome of the model species Chlamydomonas reinhardtii has been analyzed during 120 h of sulphur depletion to induce anaerobic hydrogen (H2) production, using nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled to mass spectrometry (GC/MS) and thin layer chromatography (TLC). The results indicate that these unicellular green algae consume freshly supplied acetate in the medium to accumulate energy reserves during the first 24 h of sulphur depletion. In addition to the previously reported accumulation of starch, large amounts of triacylglycerides (TAG) were deposited in the cells. During the early 24 h to 72 h time period fermentative energy metabolism lowered the pH, H2 was produced and amino acid levels generally increased. In the final phase from 72 h to 120 h, metabolism slowed down leading to a stabilisation of pH, even though some starch and most TAG remained. We conclude that H2 production does not slow down due to depletion of energy reserves but rather due to loss of essential functions resulting from sulphur depletion or due to a build-up of the toxic fermentative products formate and ethanol.