The Metal Requirements of Bacillus subtilis

Abstract

Metal ions are essential for many biological processes across all domains of life. In Bacillus subtilis, they function as essential cofactors for enzymes, a component of biosensors for oxidative damage, in the assembly of the ribosome, in the folding of mRNA, and a myriad of other processes. In Bacillus subtilis, the minimum metal quota per cell to sustain growth has not previously been established. In this study, we establish a metal-limited minimal medium that enables us to probe the interaction of metals at the thresholds for growth and determine how the cell responds to limitation. Here we determine the minimum concentrations of magnesium, iron, and manganese needed for full growth. Furthermore, these requirements are dependent on the levels of all metals within the total metal pool. We were unable to demonstrate any growth limitation in the absence of added zinc in wildtype cells; however, in cells mutant in the zinc importer, encoded by znuC, zinc is limiting for growth. Development of this medium allows us to examine how cells adapt to trace metal availability. Under iron-limited conditions, the cell initiates an iron-sparing response. In the absence of the regulator of this response, fsrA, the cells require higher iron for growth. Not only does this media give us insight into the complex balance of intracellular metal pools, but it provides a tool for the analysis of metal limitation in Bacillus subtilis.