Microbial Endocrinology: Interaction of the Microbial Hormones with the Host

Abstract

Recent studies of the human microbial ecology, studying the communities of bacteria within the human bodies. The genetic information of the bacteria within the human bodies can be 150-fold greater than the human genome. A complicated interaction between the host and the microbial gut. Indeed, the gut microbiota plays important roles in host metabolism, immunity and even behavior. Mechanisms by which the microbiota are known to mediate these functions include breaking down dietary components, educating the immune system and degrading toxins [1-3]. In recent years modulation of hormonal secretion revealed the nature of the host bacteria interaction. Actually, direct after birth, bacterial colonizating the intestine perform by a critical role in the maturation of the immune system [2] and the endocrine system (Clarke 2013). Hormone Production by Bacteria Bacteria can produce hormones that can affect host metabolism, immunity and behavior. This interplay is bidirectional, because the microbiota has shown to be both affected by and to affect host hormones, this can be called microbial endocrinology. Lyte and Ernst were the first to define the field of microbial endocrinology research, after observing that stress-induced neuroendocrine hormones can influence bacterial growth [4]. More researches concerned with microbial endocrinology discovered hormone receptors in microorganisms and hypothesized that they represent a form of intercellular communication [5]. As an example, pathogenic neurotoxins such as neurotoxin 6-hydroxydopamine were shown to alter norepinephrine levels in mice presenting the bidirectional nature of the host-microbe interaction [6]. An interesting study showed that many enzymes involved in host hormone metabolism (including epinephrine, norepinephrine, dopamine, serotonin, melatonin, etc.) might have evolved from horizontal gene transfer from bacteria [7]. Crosstalk between bacteria and the endocrine system came from the discovery of interkingdom signaling, including the hormonal communication between microorganisms and their hosts [8]. This field evolved from the initial observation that bacteria perform quorum sensing (QS), communication based on producing and sensing autoinducer (AI) molecules. These AI molecules are hormone-like elements that regulate functions including coordinated bacterial growth, motility and virulence [9]. Some AI molecules have crosstalk with host hormones for activating signaling pathways [10]. The hormone of the human host can affect the bacterial gene expression [11], for example, catecholamines enhance bacterial attachment to host tissues, and affect growth and virulence of