Phenazines

Phenazines are a class of nitrogen-containing heterocyclic secondary metabolites characterized by a fused three-ring core known as the phenazine nucleus. They commonly appear as yellow to blue pigments and are redox-active, capable of cycling between oxidized and reduced states in chemical and biological systems.

Natural occurrence and biosynthesis: Phenazines are produced by diverse bacteria, notably Pseudomonas species and Streptomyces, and to a lesser extent by fungi. In Pseudomonas, production is governed by phz gene clusters that convert chorismate via a multi-enzyme pathway to phenazine-1-carboxylic acid (PCA), the central scaffold from which other phenazines, such as pyocyanin and phenazine-1-carboxamide, are derived. Production is regulated by environmental cues and quorum sensing.

Biological roles and properties: Phenazines act as antimicrobial agents and virulence factors; compounds like pyocyanin generate reactive oxygen species in host tissues and microbial competitors. In ecology, they function as extracellular electron shuttles, enabling respiration by transferring electrons to insoluble minerals, influencing biofilm formation and biogeochemical processes.

Applications and considerations: Because of their redox activity and antimicrobial properties, phenazines are investigated for biocontrol, bioremediation, and bioelectronic applications, as well as historic use as pigments. Safety concerns include toxicity to other organisms and potential health risks, so research emphasizes containment and risk assessment.