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A possibility of release of an extracellular c-type cytochrome by Geobacter sulfurreducens is discussed. Results indicate that 9.6-kDa cytochrome is not an effective shuttle between G. sulfurreducens and Fe(III) oxide.

Humic substances were used to examine the electron-mediating ability of quinones moieties during the transfer of electrons from microorganisms. The humics-reducing microorganism 'Geobacter metallireducens' was considered in recognition of its ability to transfer electrons in different environments. Results showed the importance of electron-accepting ability and radical content. It as also shown that the transfer of electrons to humic substances by humics-reducing microorganisms directly influence the number of organic radicals.

Research was conducted to determine the microorganisms responsible for the microbial reduction of humic substances in sedimentary environments. Humic-reducing bacteria were isolated from various sediment types such as lake sediments, marine sediments and contaminated wetland sediments. Results indicate that in all the types of sediments that were analyzed, the acetate-oxidizing humic-reducing microorganisms recovered belonged to the Geobacteraceae family.

Geobacter metallireducens and Shewanella alga use humic substances to reduce Fe(III) oxides and act as electron acceptors during the anaerobic oxidation of organic compounds and hydrogen. This electron transport produces energy for development. Humic substances help in electron transfer between the humic-reducing microorganisms and the Fe(III) oxide. This finding has significant implications regarding the mechanisms for microbial oxidization of natural and contaminant organics in anaerobic soils and sediments.

Research was conducted to examine the role of humic-bound iron as an electron transfer agent in dissimilatory Fe(III) reduction. Results demonstrate that the electron-accepting abilities of a wide range of highly purified humic substances were a lot higher than the electron-accepting abilities of the microbially reducible Fe(III). This showed that Fe(III) in humic substances can at best account for a small amount of the initial electron transfer to humic substances in environments in which Fe(III) reduction is the terminal electron-accepting process.

Reports on the general consideration that sulphur reduction was one of the earliest forms of microbial respiration, because the known microorganisms that are most common ancestors of modern life are primarily anaerobic, sulphur-reducing hyperthermophiles. Details of microbial evidence of iron on early Earth and the role it could have played in the creation of the biosphere.