The Cul3–KLHL21 E3 ubiquitin ligase targets Aurora B to midzone microtubules in anaphase and is required for cytokinesis

Selective ubiquitination of Aurora B by different Cul3 adaptors targets it at the correct time to the correct place during mitosis

Intracellular Vesicles as Reproduction Elements in Cell Wall-Deficient L-Form Bacteria

Cell wall-deficient bacteria, or L-forms, represent an extreme example of bacterial plasticity. Stable L-forms can multiply and propagate indefinitely in the absence of a cell wall. Data presented here are consistent with the model that intracellular vesicles in Listeria monocytogenes L-form cells represent the actual viable reproductive elements. First, small intracellular vesicles are formed along the mother cell cytoplasmic membrane, originating from local phospholipid accumulation. During growth, daughter vesicles incorporate a small volume of the cellular cytoplasm, and accumulate within volume-expanding mother cells. Confocal Raman microspectroscopy demonstrated the presence of nucleic acids and proteins in all intracellular vesicles, but only a fraction of which reveals metabolic activity. Following collapse of the mother cell and release of the daughter vesicles, they can establish their own membrane potential required for respiratory and metabolic processes. Premature depolarization of the surrounding membrane promotes activation of daughter cell metabolism prior to release. Based on genome resequencing of L-forms and comparison to the parental strain, we found no evidence for predisposing mutations that might be required for L-form transition. Further investigations revealed that propagation by intracellular budding not only occurs in Listeria species, but also in L-form cells generated from different Enterococcus species. From a more general viewpoint, this type of multiplication mechanism seems reminiscent of the physicochemical self-reproducing properties of abiotic lipid vesicles used to study the primordial reproduction pathways of putative prokaryotic precursor cells

Genome Sequences of Three Frequently Used Listeria monocytogenes and Listeria ivanovii Strains

We present the complete de novo assembled genome sequences of Listeria monocytogenes strains WSLC 1001 (ATCC 19112) and WSLC 1042 (ATCC 23074) and Listeria ivanovii WSLC 3009, three strains frequently used for the propagation and study of bacteriophages because they are presumed to be free of inducible prophages.ISSN:2169-828

<i>Enterococcus</i> L-form cells.

<p><i>E. faecium</i> (A) and <i>E. faecalis</i> (B) L-form cells were generated and stained with Rho123 (10 µg ml⁻¹) to indicate charged membranes. In contrast to <i>Listeria</i> L-forms, the intracellular vesicles of <i>Enterococcus</i> L-forms still enclosed in the mother cell cytoplasm frequently feature stronger phase contrast (upper panels) and more intense Rho123 accumulation and fluorescence (lower panels).</p

L-form cells feature intracellular viable progeny vesicles.

<p>The viability of progeny vesicles was assessed by GFP synthesis and fluorescence (A–C), spatial distribution of Rho123 (D–F), and reductive metabolism of a tetrazolium dye (G–I). Intracellular vesicles either showed no signals, faint signals, or strong signals, in some cases stronger than the mother cell. Panel J shows baseline corrected and normalized Raman spectra of the average background control (lower curve, n = 10), mother cell cytoplasm with a strong GFP signal (middle curve, n = 13) and non-fluorescent large intracellular vesicles (upper curve, n = 18). The different spectral curves have been offset but the scale was retained. Relevant peaks are indicated by red boxes, and correspond to vibration signals from RNA/DNA (785 cm⁻¹, 1583 cm⁻¹), and proteins (1003 cm⁻¹, 1583 cm⁻¹ and 1666 cm⁻¹). These molecules are present both in the mother cell cytoplasm and, albeit less pronounced, inside the intracellular progeny vesicles. Panel K shows a box plot of Raman intensities measured for the background (buffer), mother cell cytoplasm, and intracellular vesicles at 1666 cm⁻¹, which reflects protein content. The median intensity is lower in intracellular vesicles compared to the mother cell cytoplasm, indicating a slightly lower protein content in the progeny vesicles.</p

Release of internal vesicles.

<p>(A) Following collapse of an L-form mother cell, intact progeny cells are released. Membranes are visible by using DIC (Differential Interference Contrast) microscopy (left); dye-labeled membranes (right) are shown immediately before (upper) and after the collapse (lower). (B) A vesiculated cell labeled with Rho123 (upper) disintegrates and releases a vesicle (lower image, arrow head). The increase in the Rho123 signal on the surface of the released vesicle suggests an increase in membrane charge.</p

Origin of intracellular vesicles.

<p>(A) First, uniformity of the unilamellar membrane structure is disturbed and phospholipids accumulate along the membrane. (B) Small intracellular vesicles are always generated in direct proximity to these lipid domains (left), and cytoplasmic material of the maternal cell is encapsulated into the vesicles as visualized by the compartmentalization of GFP (right). Membranes stained with CellTrace BODIPY TR methyl ester and cytoplasmic GFP fluorescence are shown in red and green, respectively. All images are confocal. (D) Current model for vesicle genesis. Lipid accumulations act as a pool for incorporation of phospholipids into a membrane structure, resulting in enlargement of intracellular progeny vesicles by a self-organizing, spontaneous process typical for bipolar phospholipids.</p