Name: Maria J.
Date: March 2004
Which evolved first gram-positive cell or gram-negative cell?
This isn't an easy question to answer, since it's difficult to determine cell wall
structure from the limited bacterial fossil records available. However, the most
primitive true bacteria in existence are the green & purple/sulfur & nonsulfur bacteria
and the cyanobacteria, all of which are gram-negative. This would suggest that the
primordial eubacterium may have been gram-negative, too. But it has also been argued
that the more simplistic structure of the gram-positive cell wall indicates that the
primordial eubacterium is more likely to have been gram-positive, as well. This debate
appeared to have been settled by fairly recent gene sequence comparisons, reported as
follows in an article entitled, "The Gram Stain and Microbial Classification", from the
Society for Anaerobic Microbiology:
"The application of comparative sequence analysis of informational macromolecules had a
profound effect on recent thinking in microbial systematics and evolution and the
emphasis placed on the Gram reaction has now been superseded by comparative 16S rRNA
sequence analysis. On the basis of this method Aquifex pyrophilis was shown to belong
to an ancient phlyletic line of eubacteria and the finding that this species possessed a
Gram-negative type cell wall refutes a dichotomous classification system based on cell
wall structure and supports a polyphyletic origin of Gram-negative bacteria." -
Although this appears to support the argument for a gram-negative eubacterial ancestry,
the article goes on to cite newer evidence indicating that there may not be a discrete
separation betwen the gram-negative & -positive eubacteria, similar to the situation in
So the answer to your question is, probably gram-negative, but stay tuned for new evidence
that could prove otherwise. Finally, there are some nice General Microbiology lecture
notes from Miami Univ. of Ohio on "Microbial Evolution and Systematics" that provide a
nice, general overview of the Origin of Microbial Life on Earth, if you're interested
( http://www.cas.muohio.edu/~stevenjr/mbi202/evolution202.html ).
Thanks a lot for the great question,
Jeff Buzby, Ph.D.
CHOC Research Institute
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