Bacillus subtilis Cell Cycle as Studied by Fluorescence Microscopy: Constancy of Cell Length at Initiation of DNA Replication and Evidence for Active Nucleoid Partitioning

Abstract

Fluorescence microscopic methods have been used to characterize the cell cycle of Bacillus subtilis at four different growth rates. The data obtained have been used to derive models for cell cycle progression. Like that of Escherichia coli, the period required by B. subtilis for chromosome replication at 37°C was found to be fairly constant (although a little longer, at about 55 min), as was the cell mass at initiation of DNA replication. The cell cycle of B. subtilis differed from that ofE. coli in that changes in growth rate affected the average cell length but not the width and also in the relative variability of period between termination of DNA replication and septation. Overall movement of the nucleoid was found to occur smoothly, as in E. coli, but other aspects of nucleoid behavior were consistent with an underlying active partitioning machinery. The models for cell cycle progression in B. subtilis should facilitate the interpretation of data obtained from the recently introduced cytological methods for imaging the assembly and movement of proteins involved in cell cycle dynamics.

The replicated ftsQAZ and minB chromosomal regions of Escherichia coli segregate on average in line with nucleoid movement

“…Many of the forces behind the presumed movements of DNA regions have not been found yet. A mitotic-like mechanism that actively segregates DNA has been suggested (for a review, see Glaser et al, 1997;Shapiro and Losick, 1997;Sharpe et al, 1998), and it has also been suggested that this mechanism exists alongside a mechanism for gradual movement of bulk DNA (Sharpe et al, 1998). We would like to add the possibility that DNA regions exhibit constrained diffusional motion, similar to that found in yeast and Drosophila (Marshall et al, 1997).…”

Several distinct localization patterns for penicillin‐binding proteins in Bacillus subtilis

“…DNA manipulations and E. coli DH5α transformations were carried out using standard methods (Sambrook et al, 1989). Solid medium used for growing B. subtilis was nutrient agar (Oxoid), and liquid medium was either casein hydrolysate (CH) medium (Sterlini and Mandelstam, 1969) or S medium (Sharpe et al, 1998) supplemented with 1% (v/v) CH (S+), with antibiotics added as required. Chloramphenicol was used at 5 µg ml −1 , spectinomycin at 50 µg ml −1 , erythromycin at 1 µg ml −1 , kanamycin at 5 µg ml −1 and phleomycin at 0.2 µg ml −1 .…”

Roles for MreC and MreD proteins in helical growth of the cylindrical cell wall in Bacillus subtilis

“…For growth experiments, B. subtilis strains were grown at 37∞C in Difco Antibiotic Medium 3 (PAB) supplemented with 0.5 M sucrose, 20 mM maleic acid and 20 mM MgCl 2 (MSM) (Chang and Cohen, 1979) or with 0.5 M sucrose or 20 mM MgCl 2 alone and 0.5% xylose was added as necessary. For imaging of GFP fluorescence strains were grown at 30∞C in S medium (Sharpe et al, 1998) with 0.3% xylose or CH medium with 0.3% xylose and 20 mM MgCl 2 . For VAN-FL staining strains were grown at 30∞C PAB supplemented as before.…”