Geology Reference
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distinct from the isotopic signal from the bulk organic biomass in those sediments
and therefore represent a different carbon pool (Damsté and Schouten
1997
).
Further, it has been demonstrated that bacteria do not contain any form of refrac-
tory macromolecular carbon, as is present in some algae and plant cuticles (de
Leeuw et al.
2006
) thus rendering bacterial biomass particularly labile (Allard
et al.
1997
; Damsté and Schouten
1997
). However, in other locations (Moers et al.
1993
) bulk organic carbon and bacterial markers have similar isotope signatures
making the claim of Hartgers et al. (
1994
), debatable. In this study we experi-
mentally 'fossilised' pure cultures of
Oscillatoria
sp. (a cyanobacterium) as this
bacterium has a geologically signifi cant contribution (Westall and Folk
2003
).
Experiments were conducted in the laboratory by placing biomass in sealed gold
tubes, and heating the cultures at 350 and at 260 °C independently at a hydro-
static pressure of 700 atmospheres for one day to simulate organic metamor-
phism in natural sediments (Stankiewicz et al.
2000
; Gupta et al.
2006
,
2007
) to
understand the organic fossilization of bacteria, and to understand if bacterial
biomass can contribute to the recalcitrant part of sedimentary organic matter
(Harvey and Macko
1997
; Head et al.
1995
).
Materials and Methods
Pure cultures of
Oscillatoria
grown in aseptic conditions at the Geobiology lab at
Carnegie were heated in sealed gold cells at 350 and 260 °C under a hydrostatic
pressure of 700 bar (Michels et al.
1995
) for 24 h in the absence of water. These
conditions were chosen because, during a previous investigation of arthropods
(Stankiewicz et al.
2000
; Gupta et al.
2006
) and modern leaves (Gupta et al.
2007
,
2009
), these revealed the most dramatic change in chemical composition to a
macromolecule with signifi cant aliphatic content. Pure C
16
and C
18
fatty acid mix-
ture (Sigma-Aldrich) was hydrothermally treated to investigate the transformation
of pure lipids as detected in the extractable and hydrolysable fraction of the bacteria.
Bacterial residue obtained after heating were extracted ultrasonically in
dichloromethane-methanol (2:1 v/v) and then subjected to thermodesorption of
weakly bound or non-covalently bound components at 310 °C (Stankiewicz et al.
2000
; Gupta et al.
2006
,
2009
) and to pyrolyse the macromolecular component.
Pyrolysis after either solvent extraction or thermodesorption yields similar results
and thermodesorption was used in all samples for thermal extraction of non-
macromolecular components after solvent extraction. The heated lipid molecules
were pyrolysed at 615 °C after thermodesorption as these were soluble in
dichloromethane-methanol, unlike the heated bacterium that was insoluble. This
paper deals with the analysis of the macromolecular component.
Hydrothermal experiments conducted at 700 bars and temperatures of 260 and
350°°C, were performed in sealed 4.5-mm OD gold cells. Prior to use, the gold
cells were annealed at 900 °C and then refl uxed in 6 N hydrochloric acid for
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