Le Tang
Harbin Medical University, China
Title: Genetic boundary to delineate bacteria into discrete natural clusters
Biography
Biography: Le Tang
Abstract
The current taxonomy classifies bacteria into largely arbitrary species, because it is still unclear whether the prokaryotes exist as natural species. Based on our previous findings that bacterial genomes are highly conserved in evolution, we hypothesize that bacteria, like all other life forms, should dwell in nature in discrete biological units, members within each of which should share common genetic and biological traits. The key evidence to support this hypothesis would be the demonstration of clear-cut genetic distinction among even very closely related bacterial lineages. To this end, we carried out systematic genomic comparisons among representative Salmonella lineages. Remarkably, we found that Salmonella, highly related from one serotype to another, formed distinct phylogenetic clusters separated by various genetic distances: whereas over 90% of the approximately four thousand shared genes had completely identical sequences among strains of the same lineage, the percentages dropped sharply to below 10% across the lineages with rare exceptions, demonstrating the existence of genetic boundaries. Recombination assays supported the genetic boundary hypothesis, showing that genetic barriers had been formed between bacteria of even very closely related lineages. We found similar situations also in other bacteria, such as Yersinia and Staphylococcus. We conclude that bacteria are genetically isolated into discrete clusters equivalent to natural species.