Pleiotropic Costs of Phage Resistance

Abstract

With pleiotropies, a single gene is responsible for more than one phenotype. As a consequence, different alleles of a single gene can differ phenotypically in more than one way. Different alleles also can give rise to different phenotypes as measured under different conditions or at different times. As a result of these pleiotropies, alleles of a single gene can be associated with improvements in one associated phenotype but also a corresponding worsening of another phenotype. The two phenotypes controlled by this one gene in a sense thereby are antagonistic to each other, hence this situation being described as an antagonistic pleiotropy. In this chapter, we again consider bacterial mutation to resistance to bacteriophages, but instead of emphasizing the primary phenotype, i.e., the phage resistance phenotype, we instead consider secondary consequences of that resistance, which we measure in general terms as bacterial evolutionary fitness in the absence of selecting phages. Thus, improvements in bacterial fitness that are seen when phages are present (condition 1), that are a consequence of bacterial mutation to phage resistance, can be associated with corresponding declines in bacterial fitness as measured especially in the absence of these phages (condition 2).