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No Ancient DNA Damage in Actinobacteria from the Neanderthal Bone
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Evolution.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Evolution.
2013 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 8, no 5, e62799- p.Article in journal (Refereed) Published
Abstract [en]

Background: The Neanderthal genome was recently sequenced using DNA extracted from a 38,000-year-old fossil. At the start of the project, the fraction of mammalian and bacterial DNA in the sample was estimated to be <6% and 9%, respectively. Treatment with restriction enzymes prior to sequencing increased the relative proportion of mammalian DNA to 15%, but the large majority of sequences remain uncharacterized. Principal Findings: Our taxonomic profiling of 3.95 Gb of Neanderthal DNA isolated from the Vindija Neanderthal Vi33.16 fossil showed that 90% of about 50,000 rRNA gene sequence reads were of bacterial origin, of which Actinobacteria accounted for more than 75%. Actinobacteria also represented more than 80% of the PCR-amplified 16S rRNA gene sequences from a cave sediment sample taken from the same G layer as the Neanderthal bone. However, phylogenetic analyses did not identify any sediment clones that were closely related to the bone-derived sequences. We analysed the patterns of nucleotide differences in the individual sequence reads compared to the assembled consensus sequences of the rRNA gene sequences. The typical ancient nucleotide substitution pattern with a majority of C to T changes indicative of DNA damage was observed for the Neanderthal rRNA gene sequences, but not for the Streptomyces-like rRNA gene sequences. Conclusions/Significance: Our analyses suggest that the Actinobacteria, and especially members of the Streptomycetales, contribute the majority of sequences in the DNA extracted from the Neanderthal fossil Vi33.16. The bacterial DNA showed no signs of damage, and we hypothesize that it was derived from bacteria that have been enriched inside the bone. The bioinformatic approach used here paves the way for future studies of microbial compositions and patterns of DNA damage in bacteria from archaeological bones. Such studies can help identify targeted measures to increase the relative amount of endogenous DNA in the sample.

Place, publisher, year, edition, pages
2013. Vol. 8, no 5, e62799- p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-205391DOI: 10.1371/journal.pone.0062799ISI: 000321202100042OAI: diva2:644284
Available from: 2013-08-29 Created: 2013-08-16 Last updated: 2014-01-23Bibliographically approved
In thesis
1. Microbial Metagenomics: A Tale of the Dead and the Living
Open this publication in new window or tab >>Microbial Metagenomics: A Tale of the Dead and the Living
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is a microbial world we live in: microbes outnumber other organisms by several orders of magnitude, and they have great importance for the environment. However, environmental microbes are notoriously difficult to grow in the laboratory, and using culture independent techniques is necessary to expand our view. In this thesis, I apply metagenomics and single-cell genomics to environmental samples from ancient human remains and lakes.

First, I used metagenomics to learn about bacteria from a Neanderthal’s bone and the gut of Ötzi, a frozen natural mummy. Both were exploratory studies where the main question was what kind of bacteria are present. I found out that Streptomyces dominated this particular Neanderthal fossil, and the DNA lacked the damage that is often seen in ancient samples. Ötzi's gut sample was dominated by Clostridia and fungi belonging to Basidiomycota.

Second, ten single-cell amplified genomes of freshwater Alphaproteobacterium LD12 and three metagenomes from Swedish lakes were sequenced. Comparative metagenomics allowed hypothesizing about which functions are important for microbe proliferation in freshwater, pointing to osmoregulation and transport proteins and, possibly, to different strategies of metabolizing sugars. I also focused on SAR11 sister-groups in oceans and lakes. Phylogenies and sequence evolutionary distance estimates indicated the existence of microclusters within LD12, showing variation in abundance between lakes. The most striking difference was the relative amount of recombination compared to mutation, the estimated r/m ratio. SAR11 marine and their freshwater cousins are found at the opposite extremes of the r/m range, lowest and highest, respectively. The genetic background or sequence diversity did not explain the observed dramatic difference, so it is possibly connected to environmental adaptation or population dynamics.

In addition, I have spent a substantial amount of effort benchmarking available metagenomic methods, for example fragment recruitment of metagenomes to reference genomes.

In conclusion, my exploratory metagenomic studies have shed some light on the bacteria present in ancient human remains; comparative metagenomics has suggested the importance of substrate preference on functional differences between lakes and oceans; finally, single-cell genomes have allowed some insight into molecular evolutionary processes taking place in the freshwater LD12 bacterium. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 108 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1067
single-cell genomics, single cell, fossil metagenome, freshwater metagenome, LD12
National Category
Microbiology Bioinformatics and Systems Biology
urn:nbn:se:uu:diva-206702 (URN)978-91-554-8742-3 (ISBN)
Public defence
2013-10-18, B41, Husargatan 3, Uppsala, 13:15 (English)
Available from: 2013-09-25 Created: 2013-09-03 Last updated: 2014-01-23

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