MTRH

mtrH is a gene encoding a multiheme c-type cytochrome associated with extracellular electron transfer in metal-reducing bacteria, most notably within Shewanella species. It is typically found in or near the mtr operon, which also includes mtrA, mtrB, and mtrC, though the exact arrangement and presence of mtrH can vary among strains.

Proteins encoded by mtrH are predicted to contain multiple heme-binding motifs (CXXCH), characteristic of c-type cytochromes, and are thought to function as soluble or periplasmic electron carriers that interact with other components of the Mtr pathway. Localization data from related species suggest a periplasmic or outer-membrane-associated role, but precise localization can differ among organisms.

Functionally, mtrH is considered to participate in the transfer of electrons from the inner membrane to outer membrane electron carriers such as MtrA and MtrC, facilitating reduction of extracellular electron acceptors such as metal oxides. In several studies, disruption of mtrH reduces iron or manganese oxide reduction rates, indicating a supporting role rather than an essential one in all contexts; redundancy or alternative pathways can compensate in some strains.

Understanding mtrH contributes to broader insights into extracellular electron transfer, biogeochemical cycling of metals, and potential applications in bioremediation and renewable energy, including microbial fuel cells. Its presence across metal-reducing bacteria highlights the diversity of electron transfer strategies used in anoxic environments.

mtrH was identified through genome sequencing and comparative genomics of Shewanella and related bacteria and has been studied using gene knockout, expression analyses, and protein characterization to elucidate its role within the Mtr pathway.