The newly discovered Mimivirus is proving to be a challenging to the basic fundamentals of the evolution of microbe to man tree of life.

The Mimivirus was serendipitously discovered in 1992 while researching Legionellosis, a potentially fatal infectious disease caused by a bacteria belonging to the genus Legionella. Since the new organism appeared to be a bacterium, it was originally named Bradfordcoccus after the city where it was discovered, Bradford, England.

More than a decade later, however, in 2003 researchers at the Université de la Méditerranée in Marseille, France published a paper in Science re-classifying Bradfordcoccus as a virus, not a bacteria. Therefore, Bradfordcoccus was re-named Acanthamoeba polyphaga mimivirus−mimivirus short for “mimicking microbe”.

While the Mimivirus is now classified by the International Committee on Taxonomy of Viruses as a virus, the genome size is larger than some bacteria with 1,181,404 DNA base pairs in length making it the largest viral genome in scientific knowledge, outstripping the next-largest virus genome by about 450,000 base pairs.

Since the size of Mimivirus is as large as a number of bacterial species, such as Rickettsia conorii and Tropheryma whipplei, and possesses a genome size greater than an number of bacterial species and codes for products previously not thought to be encoded by viruses, the most interesting question is whether the Mimivirus could qualify as a transitional evolutionary form between viruses and bacteria as would be predicted by Charles Darwin‘s theory of evolution.

In The Origin of Species, Charles Darwin argued that evolution by “natural selection generally acts with extreme slowness …by accumulating slight, successive, favorable variations.” In the virus to bacteria world, then, what are the known “slight, successive” changes between the virus and bacteria, if any?

With twenty-first century technology, the search for the “slight, successive” changes was anticipated to reveal Darwin’s Tree of Life. In these details, however, rather than filling the missing link gaps, new problems emerged.

These problems include the number of genes. Unlike other viruses, the Mimivirus with an estimated 979 protein-coding genes far exceeds the typical number for a virus.  Also, the genome of the Mimivirus has types of genes not seen in any other viruses, including aminoacyl tRNA synthetases.

In particular, the Mimivirus contains genes coding for nucleotide and amino acid synthesis that have not even been found in some bacterial species. Not only is Mimivirus unlike other viruses, the Mimivirus is even more advanced than many bacteria.

Complicating the distinction between viruses and bacteria further was the discovery in 2011 by researchers off the coast of Chile – an even larger virus than Mimivirus, a virus named a Megavirus with 1,259,197 DNA base-pairs. The Megavirus genome has been fully sequence and what’s missing are Darwin’s “slight, successive” changes. Even between these two closely related virus species only 50% of the genes are identical and only 23% of the resulting proteins show similarity.

The evidence has sent the evolution industry back to the drawing boards. David R. Wessner of Davidson College in a 2010 article published by Nature, attempts to put on the best evolutionary spin possible. The title of the article – Discovery of the Giant Mimivirus. Mimivirus is the largest and most complex virus known. Is it an evolutionary bridge between nonliving viruses and living organisms, or is it just an anomaly? – gives away the conclusion. The answer is: an anomaly.

In the article Summary section, Wessner conceds –

Questions about the nature of viruses remain quite vexing. Recent studies of the giant Mimivirus illustrate this point. Its large size and correspondingly large genome test our general ideas of viruses as small, simple entities. The existence of genes associated with translation, metabolism, DNA repair, and protein folding raises questions about the evolutionary history of viruses.

Not only are questions are certainly raised about the evolution of viruses, the easiest possible species to study, questions are raised about the foundations of the microbe to man evolutionary paradigm through “slight, successive” changes. The evolution industry is now long in the habit of writing-off the lack of “slight, successive” changes simply as an “anomaly.” Even at the micro-level, the evidence is clear: species appear as a unique creation, not as some moving-up transitional form.

Evolution was once a theory in crisis, now evolution is in crisis without a theory. The Mimivirus us the latest example why the concept of biological evolution exists as a philosophy, but not as a science.