Pulcherrimin: a bacterial swiss army knife in the iron war

Abstract

Siderophores are soluble or membrane-embedded molecules that play a major role in Fe acquisition by microorganisms. Pulcherriminic acid (PA) is a compound produced by different microbes that sequesters Fe in the precipitated pulcherrimin, but which role in Fe homeostasis remains elusive. Using Bacillus subtilis (PA producer) and Pseudomonas protegens as a competition model, we demonstrated that PA is involved in a yet undescribed Fe-managing system. When challenged by a competitor, PA production creates a local Fe(III) source, which can be retrieved via the bacillibactin siderophore produced by B. subtilis. Furthermore, precipitation of Fe(III) as pulcherrimin prevents oxidative stress in bacterial competition by restricting the Fenton reaction and deleterious ROS formation. Together, our findings uncover that PA is at the core of a counterintuitive Fe management strategy that capitalizes on controlled Fe precipitation when challenged by a competitor. This makes PA a unique and multifunction tool in the iron war.

The role and regulation of pulcherrimin during Bacillus subtilis biofilm development

“…The main reason for this phenotype is likely the elevated levels of Spo0A phosphorylation happening at the incorrect timeline of biofilm development, which are indirectly stimulated by pulcherrimin. However, the fact that a pellicle biofilm developed further in the yvmB mutant supports a recent study where it is hypothesized that bacillibactin is able to remove the iron from pulcherrimin because of its higher affinity for this metal cation 246 . Since iron is a key component for biofilm development 53,97 , and the iron captured by overproduction of pulcherrimin in the yvmB mutant was not readily available to cells, a delay in biofilm assembly occurred until bacillibactin could retrieve the iron from pulcherrimin.…”