Species concepts are key to understanding how microbes behave in natural settings, including during infectious diseases

Summary
• A species concept is central to achieving a predictive understanding of the composition, structure, and function of microbial communities, the population biology of disease outbreaks, and the emergence of new diseases.
• Molecular biology continues to have a big impact on the tradition of assigning microbial species on the basis of phenotypic similarities, and some microbiologists have used molecular cutoffs to demarcate species.
• The terms ecotype and geotype describe populations with unique distributions along ecological or physical gradients, and can be used to identify basic community units that occupy unique ecological niches or are found in distinct locations.
• Horizontal gene transfer is important as an evolutionary process and might be an important way by which microorganisms speciate.