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 in ΔmamZ. High-resolution transmission electron microscopy (HR-TEM) showed that magnetosomes in ΔmamZ were small and irregular, and rock magnetic measurements suggested that they contained immature particles. In comparison to WT of MSR-1, intracellular iron content of ΔmamZ and the complemented strains cultured with 20 µmol/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 (RT-qPCR) analysis showed that relative transcription levels of mamX and ftsZ-like genes in ΔmamZ 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 in ΔmamZ (incubated at 12 h) and the complemented strains (incubated at 12 and 18 h), reflecting 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.