4th International Conference on Applied Microbiology and Beneficial Microbes
Harbin Medical University, China
Title: Defining natural species of bacteria by a common yardstick: Universal genomic parameter to delineate bacteria into discrete phylogenetic clusters
Biography: Shu-Lin Liu
Bacteria are classified, like higher organisms into species but the current taxonomic species contain bacteria of enormous phylogenetic diversity, causing serious confusions in medical practice and other fields. Therefore, a common yardstick is badly needed for universally defining bacterial species by using a parameter that produces discrete rather than continual data to reveal clear-cut distinctions among the species. Using Salmonella as the primary model to search for such delineating genomic parameters, we found that members of a monophyletic bacterial grouping equivalent to natural species have a high percentage of their common genes sharing identical nucleotide sequences. The percentage windows are mostly broad: >70% for members within a species and <10% for bacteria between species. Similarly, broad percentage windows were also seen in Streptomyces; we propose percentages (<70%) to reflect genetic boundaries and exclude bacteria from a species. The clear-cut nature of such percentages makes them suitable as a common yardstick to define natural bacterial species. The broad percentage windows could be interpreted as the results of non-overlapping gene pools; bacteria of the same gene pool can purge less adapted members once they acquire beneficial traits, but they cannot do that across different gene pools.