The forcibly launched spores of ascomycete fungi must eject through several millimeters of nearly still air surrounding fruiting bodies to reach dispersive air flows. Because of their microscopic ...size, spores experience great fluid drag, and although this drag can aid transport by slowing sedimentation out of dispersive air flows, it also causes spores to decelerate rapidly after launch. We hypothesize that spores are shaped to maximize their range in the nearly still air surrounding fruiting bodies. To test this hypothesis we numerically calculate optimal spore shapes--shapes of minimum drag for prescribed volumes--and compare these shapes with real spore shapes taken from a phylogeny of >100 species. Our analysis shows that spores are constrained to remain within 1% of the minimum possible drag for their size. From the spore shapes we predict the speed of spore launch, and confirm this prediction through high-speed imaging of ejection in Neurospora tetrasperma. By reconstructing the evolutionary history of spore shapes within a single ascomycete family we measure the relative contributions of drag minimization and other shape determinants to spore shape evolution. Our study uses biomechanical optimization as an organizing principle for explaining shape in a mega-diverse group of species and provides a framework for future measurements of the forces of selection toward physical optima.
Spores are the most resistant form of microbial cells, thus difficult to inactivate. The pathogenic or food spoilage effects of certain spore-forming microorganisms have been the primary basis of ...sterilization and pasteurization processes. Thermal sterilization is the most common method to inactivate spores present on medical equipment and foods. High pressure processing (HPP) is an emerging and commercial non-thermal food pasteurization technique. Although previous studies demonstrated the effectiveness of thermal and non-thermal spore inactivation, the in-depth mechanisms of spore inactivation are as yet unclear. Live and dead forms of two food spoilage bacteria, a mould and a yeast were examined using scanning electron microscopy before and after the inactivation treatment. Alicyclobacillus acidoterrestris and Geobacillus stearothermophilus bacteria are indicators of acidic foods pasteurization and sterilization processes, respectively. Neosartorya fischeri is a phyto-pathogenic mould attacking fruits. Saccharomyces cerevisiae is a yeast with various applications for winemaking, brewing, baking and the production of biofuel from crops (e.g. sugar cane). Spores of the four microbial species were thermally inactivated. Spores of S. cerevisiae were observed in the ascus and free form after thermal and HPP treatments.
Different forms of damage and cell destruction were observed for each microbial spore. Thermal treatment inactivated bacterial spores of A. acidoterrestris and G. stearothermophilus by attacking the inner core of the spore. The heat first altered the membrane permeability allowing the release of intracellular components. Subsequently, hydration of spores, physicochemical modifications of proteins, flattening and formation of indentations occurred, with subsequent spore death. Regarding N. fischeri, thermal inactivation caused cell destruction and leakage of intracellular components. Both thermal and HPP treatments of S. cerevisiae free spores attacked the inner membrane, altering its permeability, and allowing in final stages the transfer of intracellular components to the outside. The spore destruction caused by thermal treatment was more severe than HPP, as HPP had less effect on the spore core. All injured spores have undergone irreversible volume and shape changes. While some of the leakage of spore contents is visible around the deformed but fully shaped spore, other spores exhibited large indentations and were completely deformed, apparently without any contents inside. This current study contributed to the understanding of spore inactivation by thermal and non-thermal processes.
•SEM is a useful tool to visualize differences between live and dead spores.•Injured bacterial, mould and yeast spores had irreversible volume and shape changes.•Thermal treatment attacked the bacterial spore inner core.•Thermally treated Neosartorya fischeri spores showed cell destruction and intracellular leakage.•Thermal treatment caused more severe damage than HPP on Saccharomyces cerevisiae ascospores.
Summary
Rhizophagus irregularis is the model species for arbuscular mycorrhizal fungi (AMF) research and the most widely propagated species for commercial plant biostimulants.
Using asymbiotic and ...symbiotic cultivation systems initiated from single spores, advanced microscopy, Sanger sequencing of the glomalin gene, and PacBio sequencing of the partial 45S rRNA gene, we show that four strains of R. irregularis produce spores of two distinct morphotypes, one corresponding to the morphotype described in the R. irregularis protologue and the other having the phenotype of R. fasciculatus.
The two spore morphs are easily distinguished by spore colour, thickness of the subtending hypha, thickness of the second wall layer, lamination of the innermost layer, and the dextrinoid reaction of the two outer spore wall layers to Melzer's reagent. The glomalin gene of the two spore morphs is identical and that of the PacBio sequences of the partial SSU‐ITS‐LSU region (2780 bp) obtained from single spores of the R. cf fasciculatus morphotype has a median pairwise similarity of 99.8% (SD = 0.005%) to the rDNA ribotypes of R. irregularis DAOM 197198.
Based on these results, we conclude that the model AMF species R. irregularis is dimorphic, which has caused taxonomic confusion in culture collections and possibly in AMF research.
Myxogastria is a group of protozoa characterized by cellular uninucleate amoeboflagellates (myxamoebae and flagellated swarm cell), acellular multinucleate plasmodia, and stationary spore‐bearing ...sporocarps. The Stemonitales is a large order in the Myxogastria and contains approximately 230 species, but only 13 species have their completed life cycles observed so far. Here, we described the life cycles of two species in Stemonitales, Stemonitopsis typhina and Stemonitis fusca by culturing in water agar medium and observing the morphogenesis of their spore germination, plasmodium, and sporocarp development. The spore‐to‐spore life cycles of Ste. typhina and S. fusca were completed in approximately 67 and 12 d, respectively. Both species possessed an aphanoplasmodium. However, the spores of Ste. typhina and S. fusca germinated by the V‐shape split and pore methods, respectively. Unlike S. fusca with an evanescent peridium, Ste. typhina produced a shiny persistent peridium which was continuous with the membrane surrounding its stalk. The information will contribute to a better understanding of their taxonomy and phylogeny.
Background. Germination is a key step for successful Bacillus anthracis colonization and systemic dissemination. Few data are available on spore germination in vivo, and the necessity of spore and ...host cell interactions to initiate germination is unclear. Methods. To investigate the early interactions between B. anthracis spores and cutaneous tissue, spores were inoculated in an intraperitoneal cell-free device in guinea pigs or into the pinna of mice. Germination and bacterial growth were analyzed through colony-forming unit enumeration and electron microscopy. Results. In the guinea pig model, germination occurred in vivo in the absence of cell contact. Similarly, in the mouse ear, germination started within 15 minutes after inoculation, and germinating spores were found in the absence of surrounding cells. Germination was not observed in macrophage-rich draining lymph nodes, liver, and spleen. Edema and lethal toxin production were not required for germination, as a toxin-deficient strain was as effective as a Sterne-like strain. B. anthracis growth was locally controlled for 6 hours. Conclusions. Spore germination involving no cell interactions can occur in vivo, suggesting that diffusible germinants or other signals appear sufficient. Different host tissues display drastic differences in germinationtriggering capacity. Initial control of bacterial growth suggests a therapeutic means to exploit host innate defenses to hinder B. anthracis colonization.
Bacillus endospores have a wide variety of important medical and industrial applications. This is an overview of the fundamental aspects of the life cycle, spore structure and factors that influence ...the spore resistance of spore-forming Bacillus. Bacillus atrophaeus was used as reference microorganism for this review because their spores are widely used to study spore resistance and morphology. Understanding the mechanisms involved in the cell cycle and spore survival is important for developing strategies for spore killing; producing highly resistant spores for biodefense, food and pharmaceutical applications; and developing new bioactive molecules and methods for spore surface display.
Bacillus cereus is a gram-positive, endospore forming pathogenic bacterium that is ubiquitous in the environment and is frequently associated with emetic and diarrheal types of foodborne illness. In ...this study, 178 samples of raw rice from retail food stores were analyzed for the presence of
B. cereus spores. Spores of
Bacillus species were found in 94 (52.8%) of the rice samples with an average concentration of 32.6 CFU/g (3.6–460 CFU/g for
B. cereus and 3.6–23 CFU/g for
Bacillus thuringiensis). Eighty three of the 94 isolates were identified as
B. cereus and 11 were identified as
B. thuringiensis.
Bacillus mycoides (240 CFU/g) was the predominant isolate in one rice sample. Using PCR the isolates were checked for the presence of the cereulide synthetase gene (
ces), the
hblA and
hblD genes of the hemolysin BL (HBL) complex and the
nheA and
nheB genes of the nonhemolytic (NHE) enterotoxin complex. The
ces gene was not identified in any of the isolates. By contrast 47 (56.6%)
B. cereus isolates possessed the
hblA and
hblD genes and 74 (89.1%) isolates possessed the
nheA and
nheB genes. As determined by commercial assay kits, forty four (53.0%) of the 83
B. cereus isolates produced both NHE and HBL enterotoxins whereas 78 (93.9%) were positive for either one or the other. Protein toxin crystals were detected visually in the 11
B. thuringiensis isolates. PCR analysis revealed 10 (90.9%) of those 11 isolates carried the
cry gene. All the
B. thuringiensis isolates were positive for NHE and HBL enterotoxins. Our results suggest that foodborne illness in the U.S. due to
B. cereus with rice as the vehicle would be most likely associated with the diarrheal-type syndrome.
Clostridium difficile is a major cause of intestinal infection and diarrhoea in individuals following antibiotic treatment. Recent studies have begun to elucidate the mechanisms that induce spore ...formation and germination and have determined the roles of C. difficile toxins in disease pathogenesis. Exciting progress has also been made in defining the role of the microbiome, specific commensal bacterial species and host immunity in defence against infection with C. difficile. This Review will summarize the recent discoveries and developments in our understanding of C. difficile infection and pathogenesis.
Fungi play an important role in plant communities and ecosystem function. As a result, variation in fungal community composition can have important consequences for plant fitness. However, there are ...relatively few empirical data on how dispersal might affect fungal communities and the ecological processes they mediate.
We established sampling stations across a large area of coastal landscape varying in their spatial proximity to each other and contrasting vegetation types. We measured dispersal of spores from a key group of fungi, the Basidomycota, across this landscape using qPCR and 454 pyrosequencing. We also measured the colonization of ectomycorrhizal fungi at each station using sterile bait seedlings.
We found a high degree of spatial and temporal variability in the composition of Basidiomycota spores. This variability was in part stochastic and in part explained by spatial proximity to other vegetation types and time of year. Variation in spore community also affected colonization by ectomycorrhizal fungi and seedling growth.
Our results demonstrate that fungal host and habitat specificity coupled with dispersal limitation can lead to local variation in fungal community structure and plant–fungal interactions. Understanding fungal communities also requires explicit knowledge of landscape context in addition to local environmental conditions.
spores incubated on plates for 2 to 98 days at 37°C had identical Ca-dipicolinic acid contents, exhibited identical viability on rich- or poor-medium plates, germinated identically in liquid with all ...germinants tested, identically returned to vegetative growth in rich or minimal medium, and exhibited essentially identical resistance to dry heat and similar resistance to UV radiation. However, the oldest spores had a lower core water content and significantly higher wet heat and NaOCl resistance. In addition, 47- and 98-day spores had lost >98% of intact 16S and 23S rRNA and 97 to 99% of almost all mRNAs, although minimal amounts of mononucleotides were generated in 91 days. Levels of 3-phosphoglyceric acid (3PGA) also fell 30 to 60% in the oldest spores, but how the 3PGA was lost is not clear. These results indicate that (i) translation of dormant spore mRNA is not essential for completion of spore germination, nor is protein synthesis from any mRNA; (ii) in sporulation for up to 91 days at 37°C, the RNA broken down generates minimal levels of mononucleotides; and (iii) the lengths of time that spores are incubated in sporulation medium should be considered when determining conditions for spore inactivation by wet heat, in particular, in using spores to test for the efficacy of sterilization regimens.
We show that spores incubated at 37°C on sporulation plates for up to 98 days have lost almost all mRNAs and rRNAs, yet the aged spores germinated and outgrew as well as 2-day spores, and all these spores had identical viability. Thus, it is unlikely that spore mRNA, rRNA, or protein synthesis is important in spore germination. Spores incubated for 47 to 98 days also had much higher wet heat resistance than 2-day spores, suggesting that spore "age" should be considered in generating spores for tests of sterilization assurance. These data are the first to show complete survival of hydrated spores for ∼100 days, complementing published data showing dry-spore survival for years.
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