Classic studies of microbial evolution (antibiotic, metal)

Joseph L. Graves Jr

Department of Biology, North Carolina A&T State University, Greensboro, NC, United States.

Studies of bacterial adaptation to antibiotics and metals (ionic and nanoparticle) have shown the capacity of these organisms to rapidly evolve. This is due to their large population size that guarantees that de novo mutation will be available as the raw material for adaptation. This chapter examined three classic studies: resistance to an antimicrobial peptide; the role of epistasis in contributing to multiple drug resistance; and the rapid evolution of gallium resistance. These experimental studies all began with the target substance at subminimum inhibitory concentrations (sub-MIC). This is a realistic feature of these experiments because even when exposure to these substances is conducted at very high concentrations, those concentrations will decline either by time or distance to sub-MIC concentrations. However, all of these studies were conducted in constant and single-species environments, suggesting that evolution in nature may be more complicated. They were also conducted in environments without plasmids [which represent ready-made genetic variation for adaptation, see Chapter 6, Three domains of life - structure and function (Bacteria, Archaea, Eucarya)]. Thus experimental laboratory evolution of resistance in microbes should be looked upon as proof of concept. There is good reason to believe that evolution of resistance of natural communities may reveal some emergent properties that we might not predict from single species examples.

Keywords: Antimicrobial peptides, epistasis, pleiotropy, MDR bacteria, experimental evolution, metal resistance.