Environmental Engineering Reference
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the sedimentary record was very well protected from further degradation. This
is in agreement with the results of fossil remains of anoxygenic photosynthetic
purple sulfur bacteria in Holocene sulfidic sediments of the meromictic Cana-
dian Mahoney Lake [13]. Within these sediments, the ratio between rDNA and
the carotenoid okenone of the predominant purple sulfur bacterium, Amoe-
bobacter purpureus , was 6 orders of magnitude lower compared to the ratio in
intact cells of Amoebobacter . This ratio also did not further decline in deeper
and older sediment layers [13]. Since we used a 0.5-m-long Niskin bottle to
collect water from the chemocline, the collected POM contained a mixture of
Chlorobium cells which were exposed to optimal and sub-optimal light con-
ditions. It can, therefore, be expected that the DNA to chlorobactene ratio in
a pure Chlorobium culture under excellent light conditions would be higher
compared to this ratio measured at the chemocline.
Interestingly, the ratio DNA:chlorobactene was 2 to 3 orders of magnitude
higher in the deeper sediment layers of the core (59-105cm) (Fig. 5f), perhaps
suggesting that at certain times of the lake history the DNA of the Chlorobium
was relatively better preserved than in the present day situation. However, it
is difficult to envisage how the preservation conditions of present-day Ace
Lake can be substantially improved since the waters below the chemocline are
anoxic, sulfide-rich, cold and characterized by the absence of light. Alterna-
tively, the increase in the DNA:chlorobactene ratio may be caused by carotenoid
diagenesis. In reducing organic carbon-rich sediments, intact chlorobactene is
known to be prone to diagenetic processes such as (partial) hydrogenation
to chlorobactane as well as the incorporation via sulfurization into macro-
molecular organic matter ( [47] and references therein). Schaeffer et al. [43]
have shown that these processes already occur in the upper sediments of the
meromictic Lake Cadagno. The relatively high abundance of DNA of GSB
between 59 and 105 cm (Figs. 5f and 5g) may thus indicate that diagenetic
products of chlorobactene were formed which would not have been detected
via UV detection during HPLC analysis. Analysis for (partially) hydrogenated
counterparts of chlorobactene indicated indeed a much higher relative contri-
bution of such diagenetic products in the sediment section at 85-87 cm (high
GSB-DNA:chlorobactene ratio) than in the section at 37-39 cm (low GSB-
DNA:chlorobactene ratio) (Table 1). This revealed that a substantial part of the
chlorobactene had become partially hydrogenated in the deeper sediments re-
sulting in substantially increased GSB-DNA:chlorobactene ratios. These results
showed that the degradation of DNA compared to chlorobactene is substan-
tially higher in the water column but that within the sediments chlorobactene
concentrations were affected by diagenesis whereas the GSB DNA remained
unaltered. In good agreement with these findings is that in the same sediment
core, the quantitative comparison of alkenones and 18S rDNA of their biologi-
cal sources (haptophytes of the order Isochrysidales) showed a good correlation
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