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Name: Maria J.
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: March 2004


Question:
Which evolved first gram-positive cell or gram-negative cell?



Replies:
Dear Maria,

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on recent thinking in microbial systematics and evolution and the emphasis placed on the Gram reaction has now been superseded by comparative 16S rRNA sequence analysis.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." -

http://www.bms.ed.ac.uk/services/webspace/sam/Articles/Article1.htm

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 the archaebacteria.

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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