Fig 1.
(A) TEM image of wild-type AMB-1 cell. (B) TEM image of wild-type RS-1 cell, scale bar 200 nm. Reprinted with permission from Rahn-Lee and colleagues. [21]. TEM, transmission electron microscopy.
Fig 2.
(A) (i) 24-pin magnetic plate (left) and 96-well plate of AMB-1 cells (right) used in Komeili and colleagues. [34]. (ii) Movement of AMB-1 cells on magnetic plate at 0 seconds, 20 seconds, and 5 minutes. (iii) Phenotype of normal magnetic cells (left) and two representative, nonmagnetic mutants (right). (B) Diagram of secondary screens to classify magnetosome mutants.
Fig 3.
AMB-1 and MSR-1 strains with defects in magnetosome formation.
(A) Wild-type, AMB-1–cell image taken from segmentation of an electron cryotomogram. MamK filaments (green) run parallel to magnetosomes (yellow). (B) Electron cryotomogram image of a ΔmamK AMB-1 cell that shows disorganized magnetosomes. Images provided by Komeili. (C) TEM image of a wild-type, AMB-1 cell. Scale bar is 0.2 μm. Close-up of magnetosomes is magnified 6×. (D) TEM image of a ΔmamT AMB-1 cell showing small, misshapen magnetosomes. Scale bar is 0.2 μm. Close-up of magnetosomes is magnified 6×. Image provided by McCausland and colleagues. (E) TEM image of a cryosection of ΔmamL AMB-1 cells showing that magnetosome membranes are absent. Scale bar is 0.2 μm. Image provided by Komeili. (F) Diagram of the stepwise process of magnetosome formation and the proteins involved from membrane invagination (1), to crystal nucleation (2), and to membrane growth and formation of a mature magnetic crystal (3). Genes that have been found to be involved at each step are listed. AMB-1, Magnetospirillum magneticum AMB-1; IM, inner membrane; OM, outermembrane; MSR-1, Magnetospirillum gryphiswaldense MSR-1; TEM, transmission electron microscopy.
Fig 4.
Barcoded transposon mutagenesis and a potential magnetic screen.
(A) Diagram of RB-TnSeq in AMB-1. Each transposon insertion carries a unique 20-nucleotide sequence that acts as a barcode. The mutated strains are pooled, and then the barcodes are mapped to their insertion site in the genome. (B) Diagram of magnetic selection with the TnSeq library using different magnetic strengths to select for a range of mutant phenotypes. From left to right, as magnetic strength applied to the column increases, strains with weaker magnetic responses will be able to stick to the column, yielding a gradient of magnetic phenotypes to analyze. AMB-1, Magnetospirillum magneticum AMB-1; BC1, barcode inserted into AMB-1 genome; gDNA, genomic DNA; N20, unique 20-nucleotide sequence; RB-TnSeq, random barcoded transposon-site sequencing; U1, universal polymerase chain reaction priming site.