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

Jing Yang,Jinhua Li,Yongxin Pan,Ying Li,Xiuliang Huang,Shuqi Li,Li Li

doi:10.1186/1471-2180-13-203

Abstract

BackgroundMagnetotactic 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.ResultsA 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.ConclusionsThe 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.

Highlights

Magnetotactic bacteria produce membrane-enveloped magnetite crystals whose formation is controlled primarily by a gene island termed the magnetosome island (MAI)
Deletion of the mamX gene had no effect on cell growth To elucidate the function of mamX in the absence of polar effect, MSR-1 was subjected to in-frame gene deletion and complementation of mamX as described in Methods
These findings indicate that MamX plays an essential role in the control of magnetosome morphology and that mamX is involved in magnetite crystal maturation in MSR-1

Summary

Introduction

Magnetotactic bacteria produce membrane-enveloped magnetite crystals (magnetosomes) whose formation is controlled primarily by a gene island termed the magnetosome island (MAI). Magnetotactic bacteria (MTB) produce nano-sized membrane-enveloped magnetic organelles termed magnetosomes, consisting of single-domain magnetite (Fe3O4) or greigite (Fe3S4) crystals that are integrated into one to several chains depending on the species [1,2]. MTB are aquatic prokaryotes that utilize the magnetosomes to align themselves relative to magnetic fields and swim toward favorable low-oxygen, nutrient-rich environments. This behavior is called magneto-aerotaxis [1,3]. In Magnetospirillum strains such as M. gryphiswaldense MSR-1, M. magneticum AMB-1, and M. magnetotacticum MS-1, the MAI conservatively contains four common gene operons: mms, mamGFDC, mamAB, and mamXY [2,6]. Recent studies have shown that the mamAB operon is necessary and sufficient for magnetite biomineralization [16,17]

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