The biogeochemical cycle of iron is tightly coupled with the storage and cycling of organic carbon including electron shuttling, complexion and adsorption processes. Coexistence of microaerophilic Fe (II)-oxidizers and anaerobic Fe (III)-reducers in environments with fluctuating redox conditions like in peatlands or coal mining lakes is a prime example of mutualism, in which both partners benefit from the sustained Fe-pool.
Chemical communication is often the driving force of mutualistic interactions within microbial communities. The excreted metabolites can positively affect the growth of co-existing organisms by providing key metabolites produced by one partner and needed by the other. The co-existence of Fe-cycling microorganisms in nature is explained by their needs to have sufficient exposure to electron donors and acceptors. Interestingly, a shared homology is observed between the genes encoding the Fe(III) reduction machinery in Shewanella oneidensis and the genes encoding the Fe(II) oxidation machinery of Sideroxydans lithotrophicus. Thus, we hypothesize that in parallel to the exchange of genetic information, additional mutualistic interactions based on the exchange of each partner’s exometabolites have been established between these Fe-cycling partner organisms.
To elucidate interaction mechanisms, we establish co-culture systems to facilitate downstream analytics on both the transcriptome and metabolome levels in close collaborations with partners from the CRC ChemBioSys. Fe-cycling microbes benefit from growth in co-culture, but our data show that diffusive metabolites play a more important role in biogeochemical processes than previously thought. Shaping the environment by a regulated inter-species biofilm formation appears to be the key mechanism underlying interactions of Fe-cycling microorganisms. Thus, a complex metabolic and transcriptomic response, but not accelerated formation of Fe-end products, drive interactions of Fe-cycling microorganisms.