An Escherichia coli Mutant That Makes Exceptionally Long Cells

Although Escherichia coli is a very small (1- to 2-μm) rod-shaped cell, here we describe an E. coli mutant that forms enormously long cells in rich media such as Luria broth, as long indeed as 750 μm. These extremely elongated (eel) cells are as long as the longest bacteria known and have no internal subdivisions. They are metabolically competent, elongate rapidly, synthesize DNA, and distribute cell contents along this length. They lack only the ability to divide. The concentration of the essential cell division protein FtsZ is reduced in these eel cells, and increasing this concentration restores division.

IMPORTANCE Escherichia coli is usually a very small bacterium, 1 to 2 μm long. We have isolated a mutant that forms enormously long cells, 700 times longer than the usual E. coli cell. E. coli filaments that form under other conditions usually die within a few hours, whereas our mutant is fully viable even when it reaches such lengths. This mutant provides a useful tool for the study of aspects of E. coli physiology that are difficult to investigate with small cells.      

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Diverse uncultivated ultra-small bacterial cells in groundwater

Bacteria from phyla lacking cultivated representatives are widespread in natural systems and some have very small genomes. Here we test the hypothesis that these cells are small and thus might be enriched by filtration for coupled genomic and ultrastructural characterization. Metagenomic analysis of groundwater that passed through a ~0.2-μm filter reveals a wide diversity of bacteria from the WWE3, OP11 and OD1 candidate phyla. Cryogenic transmission electron microscopy demonstrates that, despite morphological variation, cells consistently have small cell size (0.009±0.002 μm³). Ultrastructural features potentially related to cell and genome size minimization include tightly packed spirals inferred to be DNA, few densely packed ribosomes and a variety of pili-like structures that might enable inter-organism interactions that compensate for biosynthetic capacities inferred to be missing from genomic data. The results suggest that extremely small cell size is associated with these relatively common, yet little known organisms.



Cryo-electron tomography images from 3D reconstructions of ultra-small bacteria.

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CRISPR/Cas is all the rage—and getting more precise and efficient.

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CRISPR (clustered, regularly interspaced, short palindromic repeats) is named for particular DNA loci that are found in many archaea and bacteria. CRISPR works with associated nucleases, including Cas9, to protect the cells from viral infection by inserting short snippets of viral DNA into the CRISPR cassette. By combining the Cas9 nuclease with a short guide RNA that’s custom-designed to bind a specific target, CRISPR/Cas can easily edit any gene you want. Just in the past year, for example, it has allowed researchers to cure a rare liver disease in mice, to excise HIV-inserted genes from human immune cells, and to block HIV from entering blood stem cells. CRISPR/Cas is easier than the other nuclease-based editing technologies, says John Schimenti of Cornell University; scientists are basically a reagent catalog and a round of PCR away from having everything they need to utilize CRISPR.

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