Inhibition of bacterial cell surface extension by various means causes blocking of macromolecular synthesis

FtsZ-Dependent Elongation of a Coccoid Bacterium

A mechanistic understanding of the determination and maintenance of the simplest bacterial cell shape, a sphere, remains elusive compared with that of more complex shapes. Cocci seem to lack a dedicated elongation machinery, and a spherical shape has been considered an evolutionary dead-end morphology, as a transition from a spherical to a rod-like shape has never been observed in bacteria. Here we show that a Staphylococcus aureus mutant (M5) expressing the ftsZ^G193D allele exhibits elongated cells. Molecular dynamics simulations and in vitro studies indicate that FtsZ^G193D filaments are more twisted and shorter than wild-type filaments. In vivo, M5 cell wall deposition is initiated asymmetrically, only on one side of the cell, and progresses into a helical pattern rather than into a constricting ring as in wild-type cells. This helical pattern of wall insertion leads to elongation, as in rod-shaped cells. Thus, structural flexibility of FtsZ filaments can result in an FtsZ-dependent mechanism for generating elongated cells from cocci.

The mechanisms by which bacteria generate and maintain even the simplest cell shape remain an elusive but fundamental question in microbiology. In the absence of examples of coccus-to-rod transitions, the spherical shape has been suggested to be an evolutionary dead end in morphogenesis. We describe the first observation of the generation of elongated cells from truly spherical cocci, occurring in a Staphylococcus aureus mutant containing a single point mutation in its genome, in the gene encoding the bacterial tubulin homologue FtsZ. We demonstrate that FtsZ-dependent cell elongation is possible, even in the absence of dedicated elongation machinery.

Staying in Shape: the Impact of Cell Shape on Bacterial Survival in Diverse Environments

Bacteria display an abundance of cellular forms and can change shape during their life cycle. Many plausible models regarding the functional significance of cell morphology have emerged. A greater understanding of the genetic programs underpinning morphological variation in diverse bacterial groups, combined with assays of bacteria under conditions that mimic their varied natural environments, from flowing freshwater streams to diverse human body sites, provides new opportunities to probe the functional significance of cell shape. Here we explore shape diversity among bacteria, at the levels of cell geometry, size, and surface appendages (both placement and number), as it relates to survival in diverse environments. Cell shape in most bacteria is determined by the cell wall. A major challenge in this field has been deconvoluting the effects of differences in the chemical properties of the cell wall and the resulting cell shape perturbations on observed fitness changes. Still, such studies have begun to reveal the selective pressures that drive the diverse forms (or cell wall compositions) observed in mammalian pathogens and bacteria more generally, including efficient adherence to biotic and abiotic surfaces, survival under low-nutrient or stressful conditions, evasion of mammalian complement deposition, efficient dispersal through mucous barriers and tissues, and efficient nutrient acquisition.

How to get (a)round: mechanisms controlling growth and division of coccoid bacteria

Bacteria come in a range of shapes, including round, rod-shaped, curved and spiral cells. This morphological diversity implies that different mechanisms exist to guide proper cell growth, division and chromosome segregation. Although the majority of studies on cell division have focused on rod-shaped cells, the development of new genetic and cell biology tools has provided mechanistic insight into the cell cycles of bacteria with different shapes, allowing us to appreciate the underlying molecular basis for their morphological diversity. In this Review, we discuss recent progress that has advanced our knowledge of the complex mechanisms for chromosome segregation and cell division in bacteria which have, deceptively, the simplest possible shape: the cocci.

mRNA detection by reverse transcription-PCR for monitoring viability over time in an Enterococcus faecalis viable but nonculturable population maintained in a laboratory microcosm

The viable but nonculturable (VBNC) state is a survival strategy adopted by bacteria when they are exposed to hostile environmental conditions. It has been shown that VBNC forms of bacteria are no longer capable of growing on conventional bacteriological media but conserve pathogenic factors and/or genes. It is thus necessary to develop methods capable of detecting nonculturable bacteria and of establishing their viability when the microbiological quality of environments is monitored. In this study we demonstrated that a gene was expressed during the VBNC state in a low-nutrient-concentration microcosm through detection of Enterococcus faecalis pbp5 mRNA by reverse transcription-PCR over a 3-month period. The presence of mRNA correlated with metabolic activity and resuscitation capability, indicating the viability of the VBNC cells.