Extracellular electron transfer of Methylophilus methylotrophs.

• Methylophilus could use ferrihydrite as an electron acceptor. • Iron-dependent metabolism supports Methylophilus to survive in oxygen-limited condition. • Cytochrome c and riboflavin are involved in extracellular electron transfer of Methylophilus. Methylophilus methylotrophs, as representatives of C1 microbes, widely exist in the interface of hyperoxia–hypoxia environment and plays a key role in global carbon cycle. Most studies of Methylophilus were carried out under hyperoxic conditions, while it remains unclear how Methylophilus survive under oxygen-limited conditions. In this study, we report that ferrihydrite could serve as an alternative electron acceptor for Methylophilus strain with reduction rate of 53.6 μM Fe(II) d−1, when cells were deprived of oxygen. Genomic analysis and electrochemical measurements suggested that two strategies, cytochrome c and riboflavin, were involved in the extracellular mineral respiration. Respiration of extracellular electron acceptor by a Methylophilus strain demonstrated in this study broadens our understanding of energy metabolism by Methylophilus and suggests as a survival strategy for these microbes under oxygen-limited conditions. The results also demonstrate Methylophilus spp. as novel type of electrochemical active microbes that could be applied in bioelectrochemical systems with single-carbon substrate. [ABSTRACT FROM AUTHOR]