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- Mazza, P., et al.
(författare)
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MreB of Streptomyces coelicolor is not essential for vegetative growth but is required for the integrity of aerial hyphae and spores
- 2006
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 60:4, s. 838-852
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Tidskriftsartikel (refereegranskat)abstract
- MreB forms a cytoskeleton in many rod-shaped bacteria which is involved in cell shape determination and chromosome segregation. PCR-based and Southern analysis of various actinomycetes, supported by analysis of genome sequences, revealed mreB homologues only in genera that form an aerial mycelium and sporulate. We analysed MreB in one such organism, Streptomyces coelicolor. Ectopic overexpression of mreB impaired growth, and caused swellings and lysis of hyphae. A null mutant with apparently normal vegetative growth was generated. However, aerial hyphae of this mutant were swelling and lysing; spores doubled their volume and lost their characteristic resistance to stress conditions. Loss of cell wall consistency was observed in MreB-depleted spores by transmission electron microscopy. An MreB-EGFP fusion was constructed to localize MreB in the mycelium. No clearly localized signal was seen in vegetative mycelium. However, strong fluorescence was observed at the septa of sporulating aerial hyphae, then as bipolar foci in young spores, and finally in a ring- or shell-like pattern inside the spores. Immunogold electron microscopy using MreB-specific antibodies revealed that MreB is located immediately underneath the internal spore wall. Thus, MreB is not essential for vegetative growth of S. coelicolor, but exerts its function in the formation of environmentally stable spores, and appears to primarily influence the assembly of the spore cell wall.
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| 3. |
- Schirner, Leonard, et al.
(författare)
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Aligned fractures on asteroid Ryugu as an indicator of thermal fracturing
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 684
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Tidskriftsartikel (refereegranskat)abstract
- Context. Asteroid and comet surfaces are exposed to a complex environment that includes low gravity, high temperature gradients, and a bombardment of micrometeorites and cosmic rays. Surface material exposed to this environment evolves in a specific way depending on various factors such as the bodiesa-size, heliocentric distance, and composition. Fractures in boulders, as seen on asteroid Ryugu, can help to determine and constrain the dominant processes eroding small-body surface materials. It is also possible to estimate fracture growth timescales based on the abundance and length of fractures in boulders.Aims. We analyse the number, orientation, and length of fractures on asteroid Ryugu to establish the relation between the fractures and the processes that may have formed them. We also compare our results to similar investigations conducted on other small bodies and estimate the timescale of fracture growth.Methods. 198 high-resolution Hayabusa2 images of asteroid Ryugu suitable for our fracture analysis were selected and map-projected. Within these images, fractures in boulders were manually mapped using the QGIS software. The fracture coordinates were extracted and the fracturesa-orientation and length were computed for 1521 identified fractures.Results. Fractures in boulders on asteroid Ryugu are found to be preferentially north-south aligned, suggesting a formation through thermal erosion. Modeling the fracture length indicates a fracture growth timescale of 30 000 to 40 000 yr, slightly younger than ages found previously for asteroid Bennu. The errors in these ages, due to uncertainties about the thermophysical parameters used in this model, are substantial (âà  à  33 000 yr +250 000 yr). However, even with these large errors, the model suggests that thermal fracturing is a geologically fast process. These times are not too dissimilar to those quoted in the literature for Ryugu and Bennu, since similar thermophysical material parameters for Ryugu and Bennu seem likely.
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