A second actin-like mamk protein in magnetospirillum magneticum AMB-1 encoded outside the genomic magnetosome island
Résumé
Magnetotactic bacteria are able to swim navigating along geomagnetic field lines. They synthesize ferromagnetic nanocrystals that are embedded in cytoplasmic membrane invaginations forming magnetosomes. Regularly aligned in the cytoplasm along cytoskeleton filaments, the magnetosome chain effectively forms a compass needle bestowing on bacteria their magnetotactic behaviour. A large genomic island, conserved among magnetotactic bacteria, contains the genes potentially involved in magnetosome formation. One of the genes, mamK has been described as encoding a prokaryotic actin-like protein which when it polymerizes forms in the cytoplasm filamentous structures that provide the scaffold for magnetosome alignment. Here, we have identified a series of genes highly similar to the mam genes in the genome of Magnetospirillum magneticum AMB-1. The newly annotated genes are clustered in a genomic islet distinct and distant from the known magnetosome genomic island and most probably acquired by lateral gene transfer rather than duplication. We focused on a mamK-like gene whose product shares 54.5% identity with the actin-like MamK. Filament bundles of polymerized MamK-like protein were observed in vitro with electron microscopy and in vivo in E. coli cells expressing MamK-like-Venus fusions by fluorescence microscopy. In addition, we demonstrate that mamK-like is transcribed in AMB-1 wild-type and DmamK mutant cells and that the actin-like filamentous structures observed in the DmamK strain are probably MamK-like polymers. Thus MamK-like is a new member of the prokaryotic actin-like family. This is the first evidence of a functional mam gene encoded outside the magnetosome genomic island. © 2010 Rioux et al.
Mots clés
actin
AMB 1 protein
bacterial protein
mamK protein
protein
unclassified drug
actin
bacterial DNA
article
bacterial gene
bacterial strain
controlled study
electron microscopy
Escherichia coli
fluorescence microscopy
gene cluster
gene duplication
gene expression
gene identification
genomic island
horizontal gene transfer
in vitro study
in vivo study
magnetosome
Magnetospirillum
Magnetospirillum magneticum
nonhuman
nucleotide sequence
protein polymerization
wild type
amino acid sequence
bacterial genome
DNA sequence
gene expression regulation
genetics
kinetics
metabolism
microfilament
molecular genetics
mutation
operon
reverse transcription polymerase chain reaction
sequence homology
transmission electron microscopy
ultrastructure
Western blotting
Magnetospirillum magneticum AMB-1
Prokaryota
Actins
Amino Acid Sequence
Bacterial Proteins
Blotting
Western
DNA
Bacterial
Gene Expression Regulation
Genome
Genomic Islands
Kinetics
Magnetosomes
Microfilaments
Microscopy
Electron
Transmission
Molecular Sequence Data
Mutation
Operon
Reverse Transcriptase Polymerase Chain Reaction
Sequence Analysis
Sequence Homology
Amino Acid