Amino acid deprivation and central carbon metabolism regulate the production of outer membrane vesicles and tubes by <i>Francisella</i>

Sampath, Vinaya; McCaig, William D.; Thanassi, David G.

doi:10.1111/mmi.13897

Cited by 32 publications

(33 citation statements)

References 77 publications

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“…Although these authors discussed that OMT formation was caused by cell stress they did not explore the possibility that some cells were dying 8 . Finally, OMTs were also found in the pathogens Francisella novidica and Francisella tularensis where OMTs were stimulated by stress conditions induced by amino-acid deprivation or during macrophage infection 49 , 50 . Nevertheless, these structures, being formed from the outer membrane, do not have to cross the cell wall and, therefore, the mechanism of their formation is likely different from that one of B. subtilis NTs.…”

Section: Discussionmentioning

confidence: 99%

Bacterial nanotubes as a manifestation of cell death

et al. 2020

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Bacterial nanotubes are membranous structures that have been reported to function as conduits between cells to exchange DNA, proteins, and nutrients. Here, we investigate the morphology and formation of bacterial nanotubes using Bacillus subtilis. We show that nanotube formation is associated with stress conditions, and is highly sensitive to the cells’ genetic background, growth phase, and sample preparation methods. Remarkably, nanotubes appear to be extruded exclusively from dying cells, likely as a result of biophysical forces. Their emergence is extremely fast, occurring within seconds by cannibalizing the cell membrane. Subsequent experiments reveal that cell-to-cell transfer of non-conjugative plasmids depends strictly on the competence system of the cell, and not on nanotube formation. Our study thus supports the notion that bacterial nanotubes are a post mortem phenomenon involved in cell disintegration, and are unlikely to be involved in cytoplasmic content exchange between live cells.

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Section: Discussionmentioning

confidence: 99%

Bacterial nanotubes as a manifestation of cell death

et al. 2020

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“…These studies further suggest at the vaccine potential of a Fn slt mutant that overproduces OMTs able to elicit an effective immune response. A more recent study found that production of OMTs was triggered by cysteine deprivation in rich medium, indicating a role for OMTs in metabolism as well as in virulence (Sampath et al, 2018). Interestingly, F. novicida transposon mutants exhibiting hyper-vesiculation had interruptions in genes involved in cell division and peptidoglycan modification, such as ftsK and carboxypeptidases like dacD .…”

Section: Discussionmentioning

confidence: 99%

A Francisella novicida Mutant, Lacking the Soluble Lytic Transglycosylase Slt, Exhibits Defects in Both Growth and Virulence

et al. 2019

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Francisella tularensis is the causative agent of tularemia and has gained recent interest as it poses a significant biothreat risk. F. novicida is commonly used as a laboratory surrogate for tularemia research due to genetic similarity and susceptibility of mice to infection. Currently, there is no FDA-approved tularemia vaccine, and identifying therapeutic targets remains a critical gap in strategies for combating this pathogen. Here, we investigate the soluble lytic transglycosylase or Slt in F. novicida , which belongs to a class of peptidoglycan-modifying enzymes known to be involved in cell division. We assess the role of Slt in biology and virulence of the organism as well as the vaccine potential of the slt mutant. We show that the F. novicida slt mutant has a significant growth defect in acidic pH conditions. Further microscopic analysis revealed significantly altered cell morphology compared to wild-type, including larger cell size, extensive membrane protrusions, and cell clumping and fusion, which was partially restored by growth in neutral pH or genetic complementation. Viability of the mutant was also significantly decreased during growth in acidic medium, but not at neutral pH. Furthermore, the slt mutant exhibited significant attenuation in a murine model of intranasal infection and virulence could be restored by genetic complementation. Moreover, we could protect mice using the slt mutant as a live vaccine strain against challenge with the parent strain; however, we were not able to protect against challenge with the fully virulent F. tularensis Schu S4 strain. These studies demonstrate a critical role for the Slt enzyme in maintaining proper cell division and morphology in acidic conditions, as well as replication and virulence in vivo . Our results suggest that although the current vaccination strategy with F. novicida slt mutant would not protect against Schu S4 challenges, the Slt enzyme could be an ideal target for future therapeutic development.

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“…Production of OMV has previously been described in F. novicida (McCaig et al, 2013) and F. tularensis subsp. tularensis SchuS4 (Sampath et al, 2017) and a novel and unusual nanotubular shape was observed. Similar structures were also found in F. noatunensis , a related fish pathogen (Brudal et al, 2015).…”

Section: Introductionmentioning

confidence: 98%

Francisella tularensis subsp. holarctica Releases Differentially Loaded Outer Membrane Vesicles Under Various Stress Conditions

et al. 2019

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Francisella tularensis is a Gram-negative, facultative intracellular bacterium, causing a severe disease called tularemia. It secretes unusually shaped nanotubular outer membrane vesicles (OMV) loaded with a number of virulence factors and immunoreactive proteins. In the present study, the vesicles were purified from a clinical isolate of subsp. holarctica strain FSC200. We here provide a comprehensive proteomic characterization of OMV using a novel approach in which a comparison of OMV and membrane fraction is performed in order to find proteins selectively enriched in OMV vs. membrane. Only these proteins were further considered to be really involved in the OMV function and/or their exceptional structure. OMV were also isolated from bacteria cultured under various cultivation conditions simulating the diverse environments of F. tularensis life cycle. These included conditions mimicking the milieu inside the mammalian host during inflammation: oxidative stress, low pH, and high temperature (42°C); and in contrast, low temperature (25°C). We observed several-fold increase in vesiculation rate and significant protein cargo changes for high temperature and low pH. Further proteomic characterization of stress-derived OMV gave us an insight how the bacterium responds to the hostile environment of a mammalian host through the release of differentially loaded OMV. Among the proteins preferentially and selectively packed into OMV during stressful cultivations, the previously described virulence factors connected to the unique intracellular trafficking of Francisella were detected. Considerable changes were also observed in a number of proteins involved in the biosynthesis and metabolism of the bacterial envelope components like O-antigen, lipid A, phospholipids, and fatty acids. Data are available via ProteomeXchange with identifier PXD013074.

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Amino acid deprivation and central carbon metabolism regulate the production of outer membrane vesicles and tubes by Francisella

Cited by 32 publications

References 77 publications

Bacterial nanotubes as a manifestation of cell death

Bacterial nanotubes as a manifestation of cell death

A Francisella novicida Mutant, Lacking the Soluble Lytic Transglycosylase Slt, Exhibits Defects in Both Growth and Virulence

Francisella tularensis subsp. holarctica Releases Differentially Loaded Outer Membrane Vesicles Under Various Stress Conditions

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