Polarity and the diversity of growth mechanisms in bacteria

Abstract

Bacterial cell growth is a complex process consisting of two distinct phases: cell elongation and septum formation prior to cell division. Although bacteria have evolved several different mechanisms for cell growth, it is clear that tight spatial and temporal regulation of peptidoglycan synthesis is a common theme. In this review, we discuss bacterial cell growth with a particular emphasis on bacteria that utilize tip extension as a mechanism for cell elongation. We describe polar growth among diverse bacteria and consider the advantages and consequences of this mode of cell elongation.

Figure 1

Phylogeny and morphology of diverse bacteria exhibiting different modes of cell growth. gyrA sequences from representative species were aligned using MUSCLE [11]. RAxML [102] reconstructed the maximum likelihood phylogeny using the JTT amino acid substitution matrix and a four-category discrete gamma distribution of sequence rate variation among sites. Red text indicates species associated with adjacent micrographs. Bacillus subtilis with fluorescent vancomycin staining at progressive stages of the cell cycle; image adapted with permission from [8]. Corynebacterium glutamicum with fluorescent vancomycin staining (red; top panel) and DivIVA localization (green; bottom panel); images reproduced with permission from [25]. Streptomyces coelicolor with fluorescent vancomycin staining (red; top) and DivIVA localization (green; bottom); images reproduced with permission from [41]. Plantomyces maris image reproduced with permission from [4].

Figure 2

Zonal cell wall synthesis establishes various patterns of bacterial growth and division. Blue regions indicate the location of cell wall synthesis activity (left), and green regions the resulting location of new peptidoglycan after synthesis (right). A. Elongation by diffuse synthesis along sidewalls. B. Elongation by synthesis in a spiral pattern along sidewalls (e.g. Bacillus). C. Division by synthesis at the septum (e.g. division at the FtsZ ring in diverse bacteria). D. Polar elongation (e.g. Corynebacterium). E. Stalk formation (e.g. Caulobacter). F. Budding (e.g. planctomycetes).