What question did this study set out to answer?

This research aims to compare iron reduction capacities and metabolic properties among cultured Melioribacteraceae species.

February 28, 2026

Iron Reduction in Members of the Family Melioribacteraceae: Metabolic Properties and Genetic Determinants of Extracellular Electron Transfer

Key Points

This research aims to compare iron reduction capacities and metabolic properties among cultured Melioribacteraceae species.
Cultured all currently available members of Melioribacteraceae.
Isolated a new Melioribacter species from an aquifer.
Used microbiological techniques, bioinformatics, and physicochemical analyses.
Analyzed growth kinetics and metabolic strategies related to iron utilization.
Constructed phylogenetic trees based on housekeeping genes.
Identified differences in ferrihydrite reduction capacities among species.
Established relationships between iron reduction strategies and ecological niches.
Found that all species possess a common set of key determinants for iron reduction.
Confirmed the central role of multiheme cytochrome Mros_1570 in iron reduction.

Abstract

Using our unique collection of all currently available cultured members of the family Melioribacteraceae, as well as a new species of the genus Melioribacter isolated from an aquifer of the Yessentuki Mineral Water Deposit, we carried out comparative experiments and revealed differences between the type strains in their capacity to reduce ferrihydrite with nonfermentable (acetate) or fermentable (cellobiose) substrates as electron donors. The cultures were analyzed using conventional microbiological techniques, bioinformatics approach, and physicochemical analysis of the solid and liquid phase. It was found that, despite the similarity of their phenotypes, the studied Melioribacteraceae species exhibited clear differences in their interaction with ferrihydrite. These differences were related to the patterns of bacterial growth kinetics, the proportions between the intensities of the respiratory and fermenting metabolisms, as well as to the evolutionary transformations of the genetic determinants of iron reduction. It was shown that all six cultured species of Melioribacteraceae possessed the same set of putative key multiheme determinants of iron reduction with identical localization within a single genomic cluster. It was found that the phylogenetic tree of Melioribacteraceae constructed by comparison of 122 housekeeping genes had the same topology as the one based on the gene of multiheme cytochrome Mros₁570. This result supports our previously proposed hypothesis about the central role of this protein in iron reduction in members of Ignavibacteria. A relationship was established between the composition of mineral phase products of microbial transformation of ferrihydrite by six Melioribacteraceae species and their strategies of Fe (III) utilization in energy metabolism: either as electron acceptors in the respiratory chain or as reducing equivalents in facilitated fermentation. The revealed differences were consistent with the ecology of the studied species, which inhabit ecological niches with different contents and compositions of organic substrates. To summarize, the study determined ecologically significant metabolic properties related to biochemical processes of iron and carbon compound oxidation/reduction by cultured members of the family Melioribacteraceae.

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