On Jul 22, 2:33 pm, "Robert Karl Stonjek"
bigpond.net.au>
wrote:
> The researchers, who included Biddle; House; Stephan C. Schuster, associate
> professor; and Jean E. Brenchley, professor, biochemistry and molecular
> biology, Penn State; and Sorel Fitz-Gibbon, assistant research molecular
> biologist at the Center for Astrobiology, UCLA, found that a large
> percentage of the microbes were Archaea, single-celled organisms that look
> like Bacteria but are different on the metabolic and genetic levels. The
> percentage of Archaea increases with depth so that at 164 feet below the sea
> floor, perhaps 90 percent of the microbes are Archaea. The total number of
> organisms decreases with depth, but there are lots of cells, perhaps as many
> as 1,600 million cells in each cubic inch.
I am not sure that Archae should be considered as distinct from
prokaryotes, the other superkingdom of bacteria. Sure, their ribosome
DNA is distinct from the other bacteria. However, the ribosome DNA is
inherited separately from their chromosomal DNA, and from their
plasmid DNA. The chromosomal DNA of the prokaryote bacteria and
archaebacteria are probably not so distinct. Lateral gene transfer
probably effects the chromosomal DNA separately from the ribosomal
DNA, and may even be different from the plasmid DNA.
I have no reference except a lecture I once attended in the
Smithsonian. There the researcher claimed that the chromosomal DNA of
archaebacteria and prokaryote bacteria in the deep sea showed signs of
high levels of mixing, unlike the ribosomal DNA. However, this makes
sense. We know that plasmids are routinely exchanged between bacteria.
The ribosomes aren't that mobile. So the ribosomes may be more
"inbred" than the chromosomes. So Woelers classification of the
"superkingdom" archae may not be as fundamental as he claimed.
Or perhaps we should look at it the opposite way. Maybe ribosomes
are more fundmental to the evolutionary process than is currently
recognized. If archaebacteria are more common in extreme environments,
maybe it is because their ribosomes are sturdier than their
chromosomes. So maybe we should straight out be classifying organisms
based on the ribosomal DNA sequences instead of their chromosomal DNA
sequences.
Consider eukaryotes (animals, plants, fungi, and protozoa). What
about differences in their ribosome DNA? Or how about differences in
their mitochondrial DNA? Within plants, what about differences in
chloroplast DNA? Maybe there are significant differences on the
species level.
It seems to me that apart from "genecentric" bias, there seems to
be a big bias toward chromosome genes. We have to rember that not all
genes are chromosomal.
>
> " These microbes influence the Earth's long-term carbon cycle and also these
> microbes may be quite ancient," says Biddle.
Thie chromosomes or their ribosomes? If you say that
archaebacteria are predominant in deep ocean sediments, then one is
speaking about ribosomes. Maybe the chromosomes aren't so ancient.
Maybe gene transfer between chromosomes has been occurring between the
deep ocean sediments organisms and the upper ocean organisms. Maybe we
should talk about "ancient" in terms of separate gene networks.
