The adaptive success of bacteria depends, in part, on the ability to sense and respond to their environment. Metals such as iron and manganese are important nutrients that can often be limiting, and therefore cellular metabolism must be modified to either scavenge the nutrients or use alternative processes that do not require the metal. Bradyrhizobium japonicum belongs to a group of related organisms that form close or intracellular and related bacteria that form an intracellular relationship with eukaryotes in a pathogenic or symbiotic context. This bacterium serves as a model to study related pathogens that are refractive to genetic and biochemical study. One project involves understanding the mechanisms by which cells maintain iron homeostasis at the level of gene expression. We discovered the global transcriptional regulator Irr that controls iron-dependent processes. Irr is stable only under iron limitation, where it positively and negatively controls target genes. We are interested in understanding the mechanism of this conditional stability, how Irr regulates genes, and the functions of numerous genes under its control. We initiated a new project to understand the requirement for manganese in cellular processes, how it is acquired from the environment, and how manganese controls gene expression. Also, we identified cross-talk between regulators that control iron and manganese homeostasis and are pursuing this unique mechanism.