Determinants of Bacterial Morphology: From Fundamentals to Possibilities for Antimicrobial Targeting

Abstract

Bacterial morphology is extremely diverse. Specific shapes are the consequence of adaptive pressures optimizing bacterial fitness. Shape affects critical biological functions, including nutrient acquisition, motility, dispersion, stress resistance and interactions with other organisms. Although the characteristic shape of a bacterial species remains unchanged for vast numbers of generations, periodical variations occur throughout the cell (division) and life cycles, and these variations can be influenced by environmental conditions. Bacterial morphology is ultimately dictated by the net-like peptidoglycan (PG) sacculus. The species-specific shape of the PG sacculus at any time in the cell cycle is the product of multiple determinants. Some morphological determinants act as a cytoskeleton to guide biosynthetic complexes spatiotemporally, whereas others modify the PG sacculus after biosynthesis. Accumulating evidence supports critical roles of morphogenetic processes in bacteria-host interactions, including pathogenesis. Here, we review the molecular determinants underlying morphology, discuss the evidence linking bacterial morphology to niche adaptation and pathogenesis, and examine the potential of morphological determinants as antimicrobial targets.

Keywords: antimicrobials; bacterial morphology; cell shape inhibitors; cytoskeleton; peptidoglycan.

FIGURE 1

Morphological plasticity and the bacterial life cycle. The scheme illustrates the continuous modulations affecting bacterial shape throughout the life cycle. These changes can be either cyclic (division cycles) or sporadic in response to changing conditions, the presence of chemicals, colonization of other organisms or environments, nutrient depletion or abundance, etc. Most shape alterations are reversible (double-headed arrows) and could be considered adaptive phenomena, whereas others are irreversible (single-headed magenta arrows) and represent bona fide morphological differentiation processes, such as sporulation (orange sphere) or polymorphic cell cycles.