Chapter 15 - What Darwin never saw: how things differ between the microbial and macroscopic world. (Horizontal gene transfer, co-selection, persister cells)

Abstract

The serious study of genetics and evolution began on diploid macroscopic organisms. This fact is a historical contingency at odds with the fact that the vast majority of organisms that exist on this (or any other planet) are microbes. Eukaryotic unicellular, diploid, and microscopic organisms vastly outnumber macroscopic organisms both in terms of individuals and species diversity. Bacteria vastly outnumber unicellular eukaryotes, and in turn viruses vastly outnumber bacteria. Yet tremendous progress has been made over the last 160 years in our understanding of the genetics and evolution of microbes. The basic mechanisms of heredity and evolution operate on this scale, but in many ways at much faster timescales. While bacterial core genomes are smaller than those of eukaryotes they can be augmented in a number of ways through horizontal gene transfer and plasmids. Horizontal gene transfer allows for the strain diversity within supposed bacterial species to be broad. Bacterial genomes are still generally less complex than those of eukaryotes, particularly as they lack a lot of the noncoding DNA found in eukaryotes. However intergenic regions and transposable genetic elements exist and their DNA can also be epigenetically modified just as in eukaryotes.