Nutrient acquisition is fundamental to the biology of microbes. Transition metals, including iron, are required for numerous essential metabolic functions and are often a limiting resource for microbial communities in diverse environments. In animals, a system of host iron binding proteins contribute to ‘nutritional immunity,’ sequestering this nutrient away from associated microbes and protecting against systemic infection. While nutritional immunity has emerged as an important determinant of microbial pathogenesis and infectious disease susceptibility, the impact of these factors on the ecology and evolution of both microbes and hosts have remained largely unexplored. Our research combines approaches from phylogenetics, biochemistry, and molecular biology to study these various aspects host-microbe associations.
We recently discovered that components of nutritional immunity represent some of the most rapidly evolving proteins among anthropoid primates. Members of the transferrin family, which sequester and transport ferric iron in numerous extracellular host environments, display signatures of adaptive evolution at protein surfaces specifically recognized by bacterial surface receptors. Using experimental molecular systems, we have shown that rapid evolution of transferrin family proteins dictates species-specific recognition by diverse pathogenic bacteria, suggesting that nutritional immunity has imposed a strong selective pressure on both host and bacterial populations over millions of years. Evidence of recent adaptation in bacterial transferrin receptors is also indicative of competition among human-associated bacteria in the upper respiratory tract. Our ongoing work seeks to both expand our understanding of the forces shaping bacterial-host molecular interactions, as well as explore the impact of nutrient metals on host-associated microbial ecology and evolution.