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Applied and Environmental Microbiology, November 1998, p. 4513-4521, Vol. 64, No. 11
Paleomicrobiology Group, Institute for the
Chemistry and Biology of the Marine Environment, University of
Oldenburg, D-26111 Oldenburg, Germany
Received 22 June 1998/Accepted 1 September 1998
Molecular remains of purple sulfur bacteria
(Chromatiaceae) were detected in Holocene sediment layers
of a meromictic salt lake (Mahoney Lake, British Columbia,
Canada). The carotenoid okenone and bacteriophaeophytin a
were present in sediments up to 11,000 years old. Okenone is specific
for only a few species of Chromatiaceae, including
Amoebobacter purpureus, which presently predominates in the chemocline bacterial community of the lake. With a
primer set specific for Chromatiaceae in combination with denaturing gradient gel electrophoresis, 16S rRNA gene sequences of
four different Chromatiaceae species were retrieved from
different depths of the sediment. One of the sequences, which
originated from a 9,100-year-old sample, was 99.2% identical to the
16S rRNA gene sequence of A. purpureus ML1 isolated
from the chemocline. Employing primers specific for A. purpureus ML1 and dot blot hybridization of the PCR
products, the detection limit for A. purpureus ML1 DNA could be lowered to 0.004% of the total community DNA. With this
approach the DNA of the isolate was detected in 7 of 10 sediment layers, indicating that A. purpureus ML1
constituted at least a part of the ancient purple sulfur bacterial
community. The concentrations of A. purpureus DNA
and okenone in the sediment were not correlated, and the ratio of DNA
to okenone was much lower in the subfossil sediment layers (2.7 · 10
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Analysis of Subfossil Molecular Remains of Purple
Sulfur Bacteria in a Lake Sediment
6) than in intact cells (1.4). This indicates
that degradation rates are significantly higher for genomic DNA than
for hydrocarbon cell constituents, even under anoxic conditions and at
the very high sulfide concentrations present in Mahoney Lake.
*
Corresponding author. Mailing address:
Paleomicrobiology Group, Institute for the Chemistry and Biology
of the Marine Environment, University of Oldenburg, P.O. Box 2503, D-26111 Oldenburg, Germany. Phone: 49-441-970-6376. Fax:
49-441-798-3583. E-mail:
j.overmann{at}palmikro.icbm.uni-oldenburg.de.
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