Microbial signaling compounds as endocrine effectors

Abstract

The major focus of this book is how chemical signals, including classic hormones, produced by the mammalian endocrine system alter the behavior of microbes residing in the host. However, it is also apparent that residential and transient microbes also produce signals within a host and that these signals are incorporated into the chemical milieu shared by mammalian and microbial cells. Therefore, this chapter explores the possibility that microbe-derived chemicals can transmit signals to host cells and alter host-cell behavior. We define the properties expected of a cross-kingdom signal, citing specific examples from the plethora of metabolites, toxins, second messengers, and other small chemicals produced by microbes. Furthermore, we describe published evidence of the potential physiological effects of microbial signals on host cells. In keeping with the classic model of endocrine signaling, we also discuss potential microbial signal-mammalian receptor interactions. Thus, this chapter extends the concept of Microbial Endocrinology by highlighting the bidirectional nature of signal exchange between host and microbe in the human microbiome, a concept termed interkingdom signaling.