Plasticity in the cell division processes of obligate intracellular bacteria

Abstract

Most bacteria divide through a highly conserved process called binary fission, in which there is symmetric growth of daughter cells and the synthesis of peptidoglycan at the mid-cell to enable cytokinesis. During this process, the parental cell replicates its chromosomal DNA and segregates replicated chromosomes into the daughter cells. The mechanisms that regulate binary fission have been extensively studied in several model organisms, including Eschericia coli, Bacillus subtilis, and Caulobacter crescentus. These analyses have revealed that a multi-protein complex called the divisome forms at the mid-cell to enable peptidoglycan synthesis and septation during division. In addition, rod-shaped bacteria form a multi-protein complex called the elongasome that drives sidewall peptidoglycan synthesis necessary for the maintenance of rod shape and the lengthening of the cell prior to division. In adapting to their intracellular niche, the obligate intracellular bacteria discussed here have eliminated one to several of the divisome gene products essential for binary fission in E. coli. In addition, genes that encode components of the elongasome, which were mostly lost as rod-shaped bacteria evolved into coccoid organisms, have been retained during the reductive evolutionary process that some coccoid obligate intracellular bacteria have undergone. Although the precise molecular mechanisms that regulate the division of obligate intracellular bacteria remain undefined, the studies summarized here indicate that obligate intracellular bacteria exhibit remarkable plasticity in their cell division processes.

Keywords: cell division; divisome; elongasome; obligate intracellular bacteria; peptidoglycan.

Figure 1

Enzymatic steps of the peptidoglycan biosynthetic pathway in gram-negative bacteria. NAM, N-acetylmuramic acid; NAG, N-acetylglucosamine; Und-P, undecaprenyl phosphate; DAP, diaminopimelic acid.

Figure 2

Regulation of FtsZ filament assembly by the Min, nucleoid occlusion, and Ter linkage systems.

Figure 3

Assembly of divisome proteins at the septum of E. coli. Divisome formation in E. coli begins with the assembly of FtsZ filaments and ends with the recruitment of FtsN.

Figure 4

The elongasome apparatus and the potential regulation of sidewall peptidoglycan synthesis. Putative active and inactive peptidoglycan synthetic complexes are shown. Figure was adapted from Liu et al., 2020 (Liu et al., 2020).

Figure 5

Steps in the polarized cell division of the C. trachomatis. Distribution of peptidoglycan and MreB and the effect of MreB, PBP2, and PBP3 inhibitors on the chlamydial division process are shown.

Figure 6

String maps (Szklarczyk et al., 2021) illustrating protein-protein interactions of the divisome and elongasome machinery of the indicated bacteria. The interaction maps of the various obligate intracellular bacteria indicate the gene products they have retained (highlighted blue) and their putative interactions based on studies from E. coli. The maps shown for the Buchnera, Wolbachia, and Anaplasma illustrate the genes retained by the Buchnera^A strains of Buchnera aphidicola, a Wolbachia pipientis strain from supergroup J, and Anaplasma phagocytophilum, respectively (see Table 2 ). The interactions indicated with black lines are based on two-hybrid studies in E. coli. The green lines represent recently identified genetic interactions in E. coli (Du et al., 2016; Park et al., 2020; Park et al., 2021). The red lines represent interactions characterized in E. coli using FRET technology (Liu et al., 2020).