David J McGee wrote:
>> Does anyone know or have thoughts on whether bacterial genomes are in a
> state of expansion (perhaps by horizontal transfer of genes, eg.
> pathogenicity islands), or in a state of reduction (eg, deletion of
> intergenic spaces to form operons). Over time can we expect bacterial
> genomes to become more compact or acquire more DNA from other sources?
>> Your thoughts are most appreciated!
>I recenly heard a talk by Dr Stewart Cole, Pasteur Institute, France,
who is closely involved in the sequencing of the Mycobacterium
tuberculosis and M. leprae genomes at the Sanger Centre, England.
The M. tuberculosis genome is 4.3 Mbp, the M. leprae one is 2.8 Mbp.
Comparing the two genomes, he concludes that M. leprae is losing DNA,
rather than M. tb acquiring. Both genomes have large regions that have
genes in the same order. But in M. leprae, there often are genes
missing. Instead, there is some non-coding sequence, that often has some
homology (partail pseudogenes) to what is found in M. tb, indicating
that DNA was lost.
On the other hand, occasionally there are genes found in M. leprae that
have no counterpart in M. tb. So overall, it is a bit of both: M. lepare
has lost a lot of genes, but has also acquired a few others.
This work has not been published yet, but you can find the available
genome sequences on www.sanger.ac.uk.
Koen De Smet
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Imperial College School of Medicine at St Mary's