Rock-making bacteria: manganese oxidation and biomineralization in pseudomonads

ABSTRACT The oxidation of manganese from Mn(II) to Mn(III) or Mn(IV) is a common trait in the Pseudomonas genus. Many pseudomonads oxidize Mn enzymatically using one or more multicopper oxidases (MnxG and McoA) and in some cases a heme peroxidase (MopA). The oxidation of Mn leads to the extracellular precipitation of reactive Mn oxides in association with extracellular polymeric substances (EPS). Here, we review the current state of knowledge on Mn oxidation and biomineralization in pseudomonads. While most of the genetic, biochemical, and physiological insights we present derive from studies on Pseudomonas putida GB-1, we also examine the mechanisms of Mn oxidation in other Mn-oxidizing pseudomonads and survey the potential for Mn oxidation across the genus through phylogenetic analysis. Although the physiological and microbial community function(s) for Mn oxidation and biomineralization have yet to be elucidated, we discuss possible roles for Mn oxidation and identify key knowledge gaps regarding the mechanism and function of this trait in the Pseudomonas genus.