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<p>To know 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, epidemiologyepidemic, and bioterrorism mitigation</p>
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<p>In bacteria, the situation is very different from eukaryotes. Bacteria exchange pieces of DNA, not whole genomes. Normally, speciation in eukaryote occur when genetic recombination occur very actively.</p> <p> </p> <p>In 2008 research indicates But, speciation in bacteria occurs when genome-wide genetic recombination events become more limited. Because there is no biological motivation for doing so. In contrast to the eukaryotes, genetic exchange between bacterial species does not hinder adaptive divergence, so the gender isolation is not important. Indeed, bacterial species that exchange genes are free to diverge without bound in all characters, neutral and adaptive.</p>
<p>There are one example that bacteria speciate to new species. At 2008, research by Richard Lenski has even shown new bacterial species evolving in the laboratory. <em>E. coli</em> cells cannot grow on citrate under oxic conditions, and that inability has long been viewed. They then exposed several identical populations of <em>E. coli</em> to an environment high in citrate and low in other energy sources. "For more than around 30,000 generations, One population eventually evolved the Cit+ function that a gene that could metabolize citrate, whereas all of the others remain Cit- and after more than 43,500 generations, the Cit- are extinct. Given that the Cit- trait is a defining feature of <em>E. coli</em>, the population that gained Cit+ could be considered a new species.</p>
