Preservation of algaenan and proteinaceous material during the oxic decay of Botryococcus braunii as revealed by pyrolysis-gas chromatography/mass spectrometry and 13C NMR spectroscopy

Abstract

Botryococcus braunii cells were grown until the late-stationary phase of growth and subsequently decomposed under oxic conditions for 201 days using a microbial consortium obtained from a freshwater lake. Degradation exhibited multi-G model kinetics, with a ‘labile’ fraction lost at a rate two to three times slower than those observed for the degradation of other previously studied phytoplankton, and a ‘refractory’ fraction lost even more slowly. Scanning electron microscopy of the 201-day detritus, as previously seen for the kerogen, indicates the preservation of cell wall material with loss of intracellular contents. Detrital samples analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and solid-state ramp-CPMAS 13C NMR, however, indicates the preservation of highly aliphatic material, algaenan, as well as ‘intrinsically labile’ proteinaceous components. These results further support the encapsulation hypothesis that proteins may be sterically protected from enzymatic attack via intimate associations with refractory, macromolecular organic matter.