from Eva C. Berglund and A. Carolin Frank writing in Horizontal Gene Transfer in Microorganisms:
Understanding the origin, evolution, maintenance, and breakdown of host-adaptation is central to diverse areas such as human health and agriculture. Horizontal gene transfer (HGT) is a recurrent theme in the evolution of host-adaptability systems. Why are these genes often successfully transferred and what is the consequence for the recipient genome? Drawing examples from the mammal-adapted bacterium Bartonella, and from plant-adapted rhizobia, we discuss the role of horizontal gene transfer in the evolution and ecology of host-adaptation.
Further reading: Horizontal Gene Transfer in Microorganisms