Evolution and Taxonomy of Bacteria, Then (1999/2000) and Now (2009)

Abstract

One decade is hardly a ripple in respect to biological evolutionary time, but can be significant in regard to the evolution of concepts based on new experimental discoveries. Despite the popularity of the simple idea that a single macromolecule, namely 16S rRNA, is a repository of the evolutionary history of bacteria and can serve as a “Rosetta Stone” for classification, I and several others considered this notion to be an egregious oversimplification. Moreover, changing the names of well-characterized bacterial species on the basis of 16S RNA sequence differences struck me as a particularly objectionable practice. These considerations led me to publish two satires (Gest, 1999/2000) which in the fullness of time can be seen to have struck the bull's eyes of their targets. An editorial sidebar in the year 2000 satire noted: “The following satire is based on Howard Gest's view that the evolutionary history of bacteria was more complex than commonly supposed and cannot be traced with accuracy using 16SrRNA sequences as the sole criterion. Indeed, during recent years, a number of reports summarizing new research findings, including evidence suggesting the widespread occurrence of lateral gene transfer, cast doubt on the validity of bacterial evolutionary phylogeny based on rRNA trees. Gest emphasizes that rRNA sequences will probably prove to be useful eventually for identifying certain kinds of taxonomic relationships, but will not serve to provide an unambiguous evolutionary phylogeny of bacteria. Accordingly, he argues that changing the names of numerous well-known genera and species on the basis of rRNA sequences is premature and counterproductive to formulation of a logical, scientific scheme of bacterial relationships and classification.” “Gest's Postulates” (1999) relate to actual free-living bacteria, and refer to “virtual bacteria” reported to exist in natural sources as indicated by detection of 16S rRNA sequences (“virtuals” are sometimes referred to by the cognoscenti as “computer bacteroids”). The “Postulates” prescribe some penalties for investigators who publish only 16s rRNA sequences and fail to isolate corresponding live organisms within a reasonable length of time.