Unraveling Bacterial Mn(II) Oxidation

Speakers:Hope A. Johnson and Bradley M. TeboThe Scripps Research Institute
La Jolla, CAAbstract
It is important to understand the fundamental mechanism of bacterial manganese(II) oxidation because it plays a role in many biogeochemical cycles and can be utilized for bioremediation. Prior work with Mn(II)-oxidizing bacteria has suggested that Mn(II) oxidation involves a multicopper oxidase, but whether this enzyme directly catalyzes Mn(II) oxidation is unknown. For a clearer understanding of microbial Mn(II) oxidation, we have undertaken biochemical studies in the model marine -proteobacterium, Erythrobacter sp. strain SD21. In vitro experiments with this strain showed the Mn(II)-oxidizing activity to be protein dependent. The optimum pH for activity was 8.0 with a specific activity of 2.5 nmol/min/mg and a Km = 204 µM. The activity is soluble which may suggest a cytoplasmic or periplasmic protein. Mn(III) is an intermediate in the oxidation of Mn(II) and likely the primary product of enzymatic oxidation by this organism. The activity is stimulated by calcium, but is not stimulated by copper in vivo or in vitro. Surprisingly, the activity was enhanced by pyrroloquinoline quinone (PQQ) and NAD+. PQQ could also rescue Pseudomonas putida MnB1 non-Mn(II)-oxidizing mutants with insertions in the anthranilate synthase gene. Partially purified Mn(II) oxidase was significantly enriched in quinones and had a UV/VIS absorption spectrum similar to a known quinoprotein but not to known multicopper oxidases, suggesting that quinones may play an integral role in bacterial Mn(II) oxidation. In addition to investigating enzymes involved in Mn(II) oxidation in laboratory model strains, we have also assayed and directly identified enzymes from the environment.

Location: Kaprielian Hall (KAP) - rielian Hall, Room 203

Audiences: Everyone Is Invited

Contact: Evangeline Reyes