Bacterial speciation

The study of evolution in the bacterial world is one of the most dynamic and exciting areas of current biological research. New analytical tools from molecular biology and the increasing wealth of data from genomics research are currently offering new insights into the nature of bacterial species and the mechanisms of speciation. These studies also promise to illuminate the early history of life on earth. Explore Evolution obscures this active area of research by claiming:

As British bacteriologist Alan Linton has noted, "Throughout 150 years of the science of bacteriology, there is no evidence that one species of bacteria has changed into another.
Explore Evolution, p. 104-5

This claim is made to imply once again that natural evolutionary mechanisms cannot account for speciation. As worded, it again misrepresents what evolutionary biology actually claims, and what research has shown. Explore Evolution ignores the hundreds of papers which address the study of speciation in bacteria. The quotation offered is from a book review by a British microbiologist affiliated with the Biblical Creation Society, hardly a credible source.

Recent research indicates that speciation in bacteria occurs when otherwise relatively frequent and genome-wide genetic recombination events become more limited.

A recent study notes that when eukaryotic organisms become reproductively isolated, their entire genomes become isolated. In bacteria, the situation is very different. Bacteria exchange pieces of DNA, not whole genomes. This study showed that "different regions of the Escherichia coli and Salmonella enterica chromosomes diverged over a ~70-million-year period. Genetic isolation first occurred at regions carrying species-specific genes, indicating that physiological distinctiveness between the nascent Escherichia and Salmonella lineages was maintained for tens of millions of years before the complete genetic isolation of their chromosomes."

Note also that the authors of this paper emphasize that their research on bacterial evolution is important for dealing with urgent practical problems. The proper identification and delineation of bacterial species plays critical roles in medical diagnosis, food safety, epidemiology, and bioterrorism mitigation.

Recent work by Richard Lenski has even shown new bacterial species evolving in the laboratory. Lenski and his student Zachary Blount note that "E. coli cells cannot grow on citrate under oxic conditions, and that inability has long been viewed as a defining characteristic of this important, diverse, and widespread species." They then exposed several identical populations of E. coli to an environment high in citrate and low in other energy sources. "For more than 30,000 generations, none of them evolved the capacity to use the citrate. [O]ne population eventually evolved the Cit+ function [a gene that could metabolize citrate], whereas all of the others remain Cit [unable to metabolize citrate] after more than 40,000 generations." Given that the Cit- trait is a defining feature of E. coli, the population that gained Cit+ could be considered a new species.

Bacterial evolution is an interesting and important field. There are also important questions to ask about what it even means for bacteria to speciate. Without offering a clear definition of a bacteria species, it is impossible to know whether it's true that scientists have not seen bacterial speciation, nor what significance that would hold if true. Without giving students that information, there's no way for them to pursue their own inquiry, again falsifying the claim that Explore Evolution is inquiry-based.


Adam C. Retchless and Jeffrey G. Lawrence (2007) "Temporal Fragmentation of Speciation in Bacteria" Science 317(5841):1093-1096. DOI: 10.1126/science.1144876

Christophe Fraser, William P. Hanage, Brian G. Spratt (2007) "Recombination and the Nature of Bacterial Speciation" Science 315(5811):476-480 DOI: 10.1126/science.1127573

Zachary D. Blount, Christina Z. Borland, Richard E. Lenski (2008) "Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli" Proc. Nat. Acad. Sci. 105(23):7899-7906

Table of Contents