Nitrogen Degradation Pathways in Actinomycetes: Key Components of Primary Metabolism Ensuring Survival in the Environment

Nitrogen is an essential element required for bacterial homeostsis. It serves as a building block for the biosynthesis of macromolecules and provides precursors for secondary metabolites. Actinomycetes have developed the ability to use various nitrogen sources and possess two central enzyme systems for nitrogen assimilation involving glutamine synthetase / glutamate synthase and glutamate dehydrogenase. Microorganisms living in habitats with changeable availability of nutrients have to cope with limited nitrogen availability in their ecological niches and developed strategies to survive under nitrogen limitation. A complex nitrogen metabolism of Actinobacteria allows the utilization of various compounds as N-sources. One such adaptation is the ability to acquire nitrogen from alternative sources like monoamines or polyamines putrescine, cadaverine, spermidine and spermine, ensuring both nutrients availability (C- and N-source) and resistance against high polyamine concentrations. Bacterial polyamine catabolism is not only important under low nitrogen availability, but it is also required to survive under high concentrations of these compounds. Such conditions can occur in diverse habitats like soil, plant tissues and human cells. Strategies of pathogenic and non-pathogenic Actinobacteria to survive in the presence of mono- and polyamines offer the possibility to combat pathogens by using their capability to metabolize polyamines as an antibiotic drug target. This work aims to summarize the knowledge on nitrogen utilization and, more specifically, catabolism of amines in actinobacterial survival and its role in nitrogen metabolism.