Microbes from a Neanderthal Bone
Katarzyna Zaremba
In 2006, a team working on sequencing Neanderthal genome published the first million
nucleotides (letters) from the genome. Having this DNA information on hand, researchers noticed
that only a small part of it was actually Neanderthal, and more than twice as much came from
bacteria. Moreover nothing could be said about the vast majority (80%) of the sequences, because
they were not similar to anything known. Bacteria in Neanderthal genome? Where did they come
from? What kind of bacteria were there?
This by-product of Neanderthal sequencing was the main subject of my project. I tried
several approaches and finally found a good tool for telling which bacterial groups were present in
the sample. Ancient DNA is damaged and consist of short pieces, therefore it is often hard to
compare it with modern, related organisms. The way out of the problem was to look for something
that does not change much in time and is very similar even in more distantly related organisms.
That is a gene making ribosomal RNA (rRNA). Ribosomes are involved in producing proteins,
something that all cells do and have done since times immemorial. It works exactly like in the
saying: show me your rRNA and I will tell you who you are! Comparisons of rRNA have a long
history in biology and there are huge amounts of rRNA sequences that people have collected by
now. A lot to compare with! The most spectacular result obtained with rRNA comparisons was the
discovery that some cells that look like bacteria at the first glance, are actually more similar to our,
eukaryotic, cells.
Armed with the rRNA searching tool I got back to the mysterious not-Neanderthal DNA
from Neanderthal. I haven't found any fungi, plants or any other organisms that belong to
eukaryotes (except Neanderthal of course). What I have found did not look like soil, or any other
environmental sample. It was actually similar to microbes found in humans. The groups of bacteria
I found (from the most to least abundant: Actinobacteria, β- and γ-proteobacteria, Firmicutes and
Bacteroidetes/Chlorobi), suggest that microbes from within the Neanderthal body, got into the bone
that was examined.
Degree project in biology spring 2007
Examensarbete i biologi, 20 p
Biology Education Centre and Department of Evolution, Genomics and Systematics ,Uppsala
University
supervisor: Siv Andersson