Little is known about the chemical mechanisms responsible for
bacterially mediated Mn(II) oxidation. Mn(IV) is the ther-
modynamically favored oxidation state in surface waters, yet
abiotic Mn(II) oxidation is slow under most environmental
conditions (1). Microbial processes catalyze the oxidation of
Mn(II) to Mn(IV) by up to five orders of magnitude faster than
surfaced catalyzed reactions (2–4), and most Mn oxides found in
soil, sediments, and aquatic environments are thus believed to be
of biogenic origin (2, 3, 5). Mn(II) oxidation catalysis has been
observed in diverse groups of bacteria and fungi (4, 6). Some of
the best examples of Mn(II) oxidizers as model organisms
include the bacteria Leptothrix discophora (7), Pseudomonas
putida (8), and spores of marine Bacillus sp. strain SG-1 (9). By
understanding the detailed enzymatic mechanisms of Mn(II)
oxidation and Mn(IV) oxide formation, we can gain further
insight into the roles of these processes in the environment and
how they tie into the global cycling of toxic and nutrient metals
and organic carbon.