On the Eco-Evolutionary Relationships of Fresh and Salt Water Bacteria and the Role of Gene Transfer in Their Adaptation

Abstract

Bacteria are ubiquitous and important members of aquatic ecosystems ranging from inland lakes to the open ocean. Since the advent of molecular approaches for investigating bacteria community composition (BCC), the biogeography of aquatic bacteria has been investigated across a wide variety of environments. In addition to illuminating important aspects of microbial ecology, these studies have unveiled the evolutionary relationships between freshwater and marine bacteria. It is now clear that marine and freshwater ecosystems are inhabited by evolutionarily distinct bacterial lineages, suggesting that environmental transitions across the marine–freshwater boundary have occurred rarely during the evolution of bacteria. In this chapter, we consider successful freshwater–marine transitions as a form of evolutionary innovation in bacteria. Here, we discuss recent genomic insights into the evolution of marine and freshwater bacteria, and the metabolic and physiological traits of aquatic bacteria that may either restrict or facilitate cross-colonization of freshwater and marine habitats. In doing so, we will also highlight the potential role that lateral gene transfer (LGT) has played in marine–freshwater transitions over the course of bacterial evolution.