MamZ protein plays an essential role in magnetosome maturation process of Magnetospirillum gryphiswaldense MSR-1

Based on analysis of gene structure of mamXY operon in Magnetospirillum gryphiswaldense strain MSR-1,we constructed a mamZ deletion mutant strain(ΔmamZ)and four complemented strains with different mamZ fragment lengths.Various cell phenotypic and physiological parameters were evaluated and compared among the wild-type(WT),mutant,and complemented strains.Cell growth rates were not notably different;however,magnetic response(Cmag)and iron uptake ability were significantly lower inΔmamZ.High-resolution transmission electron microscopy(HR-TEM)showed that magnetosomes inΔmamZ were small and irregular,and rock magnetic measurements suggested that they contained immature particles.In comparison to WT of MSR-1,intracellular iron content ofΔmamZ and the complemented strains cultured with 20mmol/L iron source was similar or slightly higher.The complemented strains were unable to synthesize mature or normal amounts of magnetosomes,apparently because of abnormal expression of the transmembrane domain of MamZ protein.Real-time reverse transcription polymerase chain reaction(RTqPCR)analysis showed that relative transcription levels of mamX and ftsZ-like genes inΔmamZ were higher at 18 h than at 12 h,suggesting that MamXY proteins play cooperative functional roles in the magnetosome maturation process.Transcription level of mms6 was significantly upregulated inΔmamZ(incubated at 12 h)and the complemented strains(incubated at 12 and 18 h),refl ecting possible interaction between MamXY and Mms6 proteins during magnetosome biosynthesis.These findings,taken together,demonstrate the essential role of MamZ in the magnetosome maturation process in MSR-1.

Electroactivity of the magnetotactic bacteria Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1

Magnetotactic bacteria reside in sediments and stratified water columns.They are named after their ability to synthesize internal magnetic particles that allow them to align and swim along the Earth’s magnetic field lines.Here,we show that two magnetotactic species,Magnetospirillum magneticum strain AMB-1 and Magnetospirillum gryphiswaldense strain MSR-1,are electroactive.Both M.magneticum and M.gryphiswaldense were able to generate current in microbial fuel cells with maximum power densities of 27 and 11μW/m^(2),respectively.In the presence of the electron shuttle resazurin both species were able to reduce the crystalline iron oxide hematite(Fe_(2)O_(3)).In addition,M.magneticum could reduce poorly crystalline iron oxide(FeOOH).Our study adds M.magneticum and M.gryphiswaldense to the growing list of known electroactive bacteria,and implies that electroactivity might be common for bacteria within the Magnetospirillum genus.