Microbial Mn(IV) reduction requires an initial one-electron reductive solubilization step

作者：Lin Hui; Szeinbaum Nadia H; DiChristina Thomas J; Taillefert Martial^*

来源：Geochimica et Cosmochimica Acta, 2012, 99: 179-192.

DOI：10.1016/j.gca.2012.09.020

Mn(IV) and Mn(II) are the most stable and prevalent forms of manganese in natural environments. The occurrence of Mn(III) in minerals and the detection of soluble Mn(III) in natural waters, however, suggest that Mn(III) is an intermediate in both the oxidation of Mn(II) and the reduction of Mn(IV). Mn(III) has recently been proposed as an intermediate during the oxidation of Mn(II) by Mn-oxidizing bacteria but has never been considered as an intermediate during the bio-reduction of Mn(IV). Here we show for the first time that microbial Mn(IV) reduction proceeds step-wise via two successive one-electron transfer reactions with production of soluble Mn(III) as transient intermediate. Incubations with mutant strains demonstrate that the reduction of both solid Mn(IV) and soluble Mn(III) occurs at the outer membrane of the cell. In addition, pseudo-first order rate constants obtained from these incubations indicate that Mn(IV) respiration involves only one of the two potential terminal reductases (c-type cytochrome MtrC and OmcA) involved in Fe(III) respiration. More importantly, only the second electron transfer step is coupled to production of dissolved inorganic carbon, suggesting that the first electron transfer reaction is a reductive solubilization step that increases Mn bioavailability. These findings oppose the long-standing paradigm that microbial Mn(IV) reduction proceeds via a single two-electron transfer reaction coupled to organic carbon oxidation, and suggest that diagenetic models should be revised to correctly account for the impact of manganese reduction in the global carbon cycle.

• 出版日期2012-12-15