Diameter of cells of a thermosensitive dnaA mutant of Escherichia coli cultivated at intermediate temperatures

Fatty Acid Availability Sets Cell Envelope Capacity and Dictates Microbial Cell Size

Nutrients-and by extension biosynthetic capacity-positively impact cell size in organisms throughout the tree of life. In bacteria, cell size is reduced 3-fold in response to nutrient starvation or accumulation of the alarmone ppGpp, a global inhibitor of biosynthesis. However, whether biosynthetic capacity as a whole determines cell size or whether particular anabolic pathways are more important than others remains an open question. Here we identify fatty acid synthesis as the primary biosynthetic determinant of Escherichia coli size and present evidence supporting a similar role for fatty acids as a positive determinant of size in the Gram-positive bacterium Bacillus subtilis and the single-celled eukaryote Saccharomyces cerevisiae. Altering fatty acid synthesis recapitulated the impact of altering nutrients on cell size and morphology, whereas defects in other biosynthetic pathways had either a negligible or fatty-acid-dependent effect on size. Together, our findings support a novel "outside-in" model in which fatty acid availability sets cell envelope capacity, which in turn dictates cell size. In the absence of ppGpp, limiting fatty acid synthesis leads to cell lysis, supporting a role for ppGpp as a linchpin linking expansion of cytoplasmic volume to the growth of the cell envelope to preserve cellular integrity.

[The Escherichia coli cell cycle]

This review summarizes present knowledge of the bacterial cell cycle with particular emphasis on Escherichia coli. We discuss data coming from three different types of approaches to the study of cell extension and division: The search for discrete events occurring once per division cycle. It is generally agreed that the initiation and termination of DNA replication and cell septation are discrete events; there is less agreement on the sudden doubling in rate of cell surface extension, murein biosynthesis and the synthesis of membrane proteins and phospholipids. We discuss what is known about the temporal relationship amongst the various cyclic events studied. The search for discrete growth zones in the cell envelope layers. We discuss conflicting reports on the existence of murein growth zones and protein insertion sites in the inner and outer membranes. Elucidation of the mechanism regulating the initiation of DNA replication. The concept of "critical initiation mass" is examined. We review data suggesting that the DNA is attached to the envelope and discuss the role of the latter in the initiation of DNA replication.

Bacterial growth and division: genes, structures, forces, and clocks

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Chloramphenicol releases a block in initiation of chromosome replication in a dnaA strain of Escherichia coli K12

DNA-DNA hybridisation experiments show that chloramphenicol induces a burst of initiation from the oriC region of a dnaA46 mutant of Escherichia coli at 36.5 degrees C but not from the isogenic dnaA+ strain. Following this stimulation of initiation is in parallel with the induced stimulation of RNA synthesis caused by chloramphenicol in the same strain. This is consistent with the hypothesis that the stimulation of initiation in the dnaA mutant is the result of the stimulation of the synthesis of an RNA species.

Chromosome replication rate and cell shape in Escherichia coli: lack of coupling

The dimensions of Rep- cells of Escherichia coli K-12 were measured and compared with those of their Rep+ isogenic cells (both Thy-), Rep- cells cultivated identically were longer (but not wider), even though both strains were wider when the rate of chromosome replication was slowed down by lowering the thymine concentration supplied. This eliminates the possibility that cell shape is determined by this rate. Simulating Thy+ phenotype by adding deoxyguanosine resulted in shorter Rep- cells when growth was faster. This excludes a simple relationship between cell elongation and growth rate, but is consistent with a linear proportionality between the rate of surface synthesis and growth. Thymine limitation of fast-growing Thy- E. coli K-12 cells is shown to result in loss of their uniform shape and production of bizarre morphologies, apparently due to imbalanced synthesis of wall components.