Open Access Research article

MamX encoded by the mamXY operon is involved in control of magnetosome maturation in Magnetospirillum gryphiswaldense MSR-1

Jing Yang13, Shuqi Li13, Xiuliang Huang13, Jinhua Li23, Li Li13, Yongxin Pan23 and Ying Li13*

Author Affiliations

1 State Key Laboratories for Agro-biotechnology and College of Biological Sciences, China Agricultural University, Beijing 100193, P. R. China

2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, P. R. China

3 France-China Biomineralization and Nano-structure Laboratory, Beijing 100193, P. R.China

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BMC Microbiology 2013, 13:203  doi:10.1186/1471-2180-13-203

Published: 11 September 2013



Magnetotactic bacteria produce membrane-enveloped magnetite crystals (magnetosomes) whose formation is controlled primarily by a gene island termed the magnetosome island (MAI). Characterization of single gene and operon function in MAI has elucidated in part the genetic basis of magnetosome formation. The mamX gene, located in the mamXY operon, is highly conserved in the MAI of all Magnetospirillum strains studied to date. Little is known regarding the function of mamX in the process of biomineralization.


A mamX deletion mutant (∆mamX) and its complemented strain (CmamX) by conjugation in M. gryphiswaldense strain MSR-1 were constructed. There were no striking differences in cell growth among ∆mamX, CmamX, and wild-type strain (WT). ∆mamX displayed a much weaker magnetic response than WT. Transmission electron microscopy revealed the presence of irregular, superparamagnetic magnetite particles in ∆mamX, in contrast to regular, single-domain particles in WT and CmamX. The phenotype of ∆mamX was similar to that of an ftsZ-like deleted mutant and mamXY operon deleted mutant reported previously. Quantitative real-time RT-PCR (qPCR) results indicated that the deletion of mamX had differential effects on the transcription levels of the other three genes in the operon.


The MamX protein plays an important role in controlling magnetosome size, maturation, and crystal form. The four MamXY proteins appear to have redundant functions involved in magnetosome formation. Our findings provide new insights into the coordinated function of MAI genes and operons in magnetosome formation.

Magnetospirillum gryphiswaldense; mamXY operon; mamX; Magnetosome; Crystal maturation