FIG 2.

Deletion of popZ in M. gryphiswaldense causes severe cell division defects. (A) Upon deletion of popZ_Mgr, highly elongated cells (up to 60 µm) were observed, which contained long, sometimes interrupted (black arrowheads) magnetosome chains (M) traversing throughout the cell, except polar regions (Ai to Aiii). Bipolar positioning of flagella (F) was not affected in the ΔpopZ_Mgr strain (Aiii and Aiv), but occasionally additional flagella were observed at ectopic positions along the cell’s body (Ai and Aii). Scale bars correspond to 1 μm (Aii and Aiv) and 3 µm (Ai and Aiii). (B) A linear correlation between cell length and number of magnetosomes was revealed for the ΔpopZ_Mgr strain, including highly elongated cells, with single chains consisting of more than 700 particles. Dotted lines indicate 95% confidence intervals (big dots) and prediction intervals (small dots). A total number of 47 cells for the ΔpopZ_Mgr strain and 54 cells for the wild type (WT [inset]) were analyzed from at least 3 independent cultures grown under standard microoxic conditions. (C) Time-lapse microscopy of the M. gryphiswaldense wild-type and ΔpopZ_Mgr strains. Division of the ΔpopZ_Mgr cell occurs at ectopic positions. Cell division events are marked with white arrowheads. Time values are given in hours and minutes. Scale bar = 3 µm. (D) Cell length distributions and (E) difference in length of both newborn daughter cells of M. gryphiswaldense wild-type, ΔpopZ_Mgr, and popZ_Mgr::popZ_Mgr-gfp strains measured from time-lapse series. Note that the cell length distribution of the popZ_Mgr::popZ_Mgr-gfp strain, as well as growth (not shown), did not differ noticeably from those of the wild type (specific growth rates determined under oxic conditions at 28°C: popZ_Mgr::popZ_Mgr-gfp strain, 0.169 ± 0.002 h⁻¹; wild type, 0.171 ± 0.006 h⁻¹). In contrast, for the ΔpopZ_Mgr strain, which exhibited cells with high variation in length, a prolonged lag phase and decreased specific growth rate of 0.140 ± 0.021 h⁻¹ were seen. In box plots, the bar indicates the median, the box the interquartile range, and the whiskers the 5th and 95th percentiles. The mean is shown as +. The number of measured cells (n) and mean and standard deviation (SD) are indicated in the graph. P values were determined by Kruskal-Wallis test with Dunn’s multiple-comparison posttest. *, P < 0.05, **, P < 0.01, ***, P < 0.001, ****, P < 0.0001; ns, not significant (P ≥ 0.05).