The Yin and Yang of Phenazine Physiology

Microorganisms are seldom solitary. They are surrounded by both clonal cells and other members of the local microbial community, and they often exist in, on, or in close proximity to multi-cellular host organisms like plants and humans. Whether in vivo during infection or in situ in the nutrient rich rhizosphere, microorganisms affect each other and the host. Phenazines, a class of secondary metabolites secreted by diverse bacteria, are best known for their antibiotic properties and have been shown to affect a broad spectrum of organisms ranging from bacteria over fungi, plants, nematodes, parasites, and humans. However, phenazines are also involved in numerous aspects of bacterial physiology like survival, iron acquisition, signaling, and biofilm formation in ways that have the potential to increase the fitness of both the phenazine-producing strain and non-producers alike. The overarching theme of this chapter is that phenazines can be beneficial or detrimental to organisms, depending on the milieu and one's perspective. In this chapter, we will highlight specific examples to discuss the yin and yang of phenazine physiology.