Sporangiospore Size Dimorphism Is Linked to Virulence of Mucor circinelloides

Mucor circinelloides is a zygomycete fungus and an emerging opportunistic pathogen in immunocompromised patients, especially transplant recipients and in some cases otherwise healthy individuals. We have discovered a novel example of size dimorphism linked to virulence. M. circinelloides is a heterothallic fungus: (+) sex allele encodes SexP and (−) sex allele SexM, both of which are HMG domain protein sex determinants. M. circinelloides f. lusitanicus (Mcl) (−) mating type isolates produce larger asexual sporangiospores that are more virulent in the wax moth host compared to (+) isolates that produce smaller less virulent sporangiospores. The larger sporangiospores germinate inside and lyse macrophages, whereas the smaller sporangiospores do not. sexMΔ mutants are sterile and still produce larger virulent sporangiospores, suggesting that either the sex locus is not involved in virulence/spore size or the sexP allele plays an inhibitory role. Phylogenetic analysis supports that at least three extant subspecies populate the M. circinelloides complex in nature: Mcl, M. circinelloides f. griseocyanus, and M. circinelloides f. circinelloides (Mcc). Mcc was found to be more prevalent among clinical Mucor isolates, and more virulent than Mcl in a diabetic murine model in contrast to the wax moth host. The M. circinelloides sex locus encodes an HMG domain protein (SexP for plus and SexM for minus mating types) flanked by genes encoding triose phosphate transporter (TPT) and RNA helicase homologs. The borders of the sex locus between the three subspecies differ: the Mcg sex locus includes the promoters of both the TPT and the RNA helicase genes, whereas the Mcl and Mcc sex locus includes only the TPT gene promoter. Mating between subspecies was restricted compared to mating within subspecies. These findings demonstrate that spore size dimorphism is linked to virulence of M. circinelloides species and that plasticity of the sex locus and adaptations in pathogenicity have occurred during speciation of the M. circinelloides complex

Expanding the Paradigms of Plant Pathogen Life History and Evolution of Parasitic Fitness beyond Agricultural Boundaries

International audienc

Transcription Factors Mat2 and Znf2 Operate Cellular Circuits Orchestrating Opposite- and Same-Sex Mating in Cryptococcus neoformans

Cryptococcus neoformans is a human fungal pathogen that undergoes a dimorphic transition from a unicellular yeast to multicellular hyphae during opposite sex (mating) and unisexual reproduction (same-sex mating). Opposite- and same-sex mating are induced by similar environmental conditions and involve many shared components, including the conserved pheromone sensing Cpk1 MAPK signal transduction cascade that governs the dimorphic switch in C. neoformans. However, the homeodomain cell identity proteins Sxi1α/Sxi2a encoded by the mating type locus that are essential for completion of sexual reproduction following cell–cell fusion during opposite-sex mating are dispensable for same-sex mating. Therefore, identification of downstream targets of the Cpk1 MAPK pathway holds the key to understanding molecular mechanisms governing the two distinct developmental fates. Thus far, homology-based approaches failed to identify downstream transcription factors which may therefore be species-specific. Here, we applied insertional mutagenesis via Agrobacterium-mediated transformation and transcription analysis using whole genome microarrays to identify factors involved in C. neoformans differentiation. Two transcription factors, Mat2 and Znf2, were identified as key regulators of hyphal growth during same- and opposite-sex mating. Mat2 is an HMG domain factor, and Znf2 is a zinc finger protein; neither is encoded by the mating type locus. Genetic, phenotypic, and transcriptional analyses of Mat2 and Znf2 provide evidence that Mat2 is a downstream transcription factor of the Cpk1 MAPK pathway whereas Znf2 functions as a more terminal hyphal morphogenesis determinant. Although the components of the MAPK pathway including Mat2 are not required for virulence in animal models, Znf2, as a hyphal morphology determinant, is a negative regulator of virulence. Further characterization of these elements and their target circuits will reveal genes controlling biological processes central to fungal development and virulence

Relationship of salt marsh vegetation zonation to spatial patterns in soil moisture, salinity and topography

An intertidal San Francisco Bay salt marsh was used to study the spatial relationships between vegetation patterns and hydrologic and edaphic variables. Multiple abiotic variables were represented by six metrics: elevation, distance to major tidal channels and to the nearest channel of any size, edaphic conditions during dry and wet circumstances, and the magnitude of tidally induced changes in soil saturation and salinity. A new approach, quantitative differential electromagnetic induction (Q-DEMI), was developed to obtain the last metric. The approach converts the difference in soil electrical conductivity (ECa) between dry and wet conditions to quantitative maps of tidally induced changes in root zone soil water content and salinity. The result is a spatially exhaustive map of edaphic changes throughout the mapped area of the ecosystem. Spatially distributed data on the six metrics were used to explore two hypotheses: (1) multiple abiotic variables relevant to vegetation zonation each exhibit different, uncorrelated, spatial patterns throughout an intertidal salt marsh; (2) vegetation zones and habitats of individual plant species are uniquely characterized by different combinations of key metrics. The first hypothesis was supported by observed, uncorrelated spatial variability in the metrics. The second hypothesis was supported by binary logistic regression models that identified key vegetation zone and species habitat characteristics from among the six metrics. Based on results from 108 models, the Q-DEMI map of saturation and salinity change was the most useful metric of those tested for distinguishing different vegetation zones and plant species habitats in the salt marsh

Cosmic-Ray Exposure History of the Norton Country Enstatite Achondrite

We report measurements of cosmogenic nuclides in up to 11 bulk samples from various depths in Norton County. The activities of 36Cl, 41Ca, 26Al, and 10Be were measured by accelerator mass spectrometry; the concentrations of the stable isotopes of He, Ne, Ar, and Sm were measured by electron and thermal ionization mass spectrometry, respectively. Production rates for the nuclides were modeled using the LAHET and the Monte Carlo N-Particle codes. Assuming a one-stage irradiation of a meteoroid with a pre-atmospheric radius of approximately 50 cm, the model satisfactorily reproduces the depth profiles of 10Be, 26Al, and 53Mn (< 6%) but overestimates the 41Ca concentrations by about 20%. 3He, 21Ne, and 26Al data give a one-stage cosmic-ray exposure (CRE) age of 115 Ma. Argon-36 released at intermediate temperatures, 36Ar(n), is attributed to production by thermal neutrons. From the values of 36Ar(n), an assumed average Cl concentration of 4 ppm, and a CRE age of 115 Ma, we estimate thermal neutron fluences of 1-4 x 1016 neutrons cm-2. We infer comparable values from epsilon 149Sm and epsilon 150Sm. Values calculated from 41Ca and a CRE age of 115 Ma, 0.2-1.4 x 1016 neutrons cm-2, are lower by a factor of approximately 2.5, indicating that nearly half of the 149Sm captures occurred earlier. One possible irradiation history places the center of proto-Norton County at a depth of 88 cm in a large body for 140 Ma prior to its liberation as a meteoroid with a radius of 50 cm and further CRE for 100 Ma. © 2011, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.co

Origin and Evolution of Water in the Moon’s Interior

Nearly forty years after the return of the first lunar samples to Earth, improvements in laboratory detection limits made possible the first definitive discovery of magmatic water in lunar volcanic samples. The intervening decade has seen an exponential increase in the amount of data on the abundance of magmatic water, and its hydrogen isotope composition, in various rock types recovered from the Moon. Here we review these data and describe how the abundance of water in the lunar interior places important constraints on models for the high-temperature origin and evolution of the Moon