Special Issue "Genetic and Functional Diversity of Microorganisms"

Abstract: Forty-five Xanthomonas arboricola pv. juglandis (Xaj) strains originating from Juglans regia cultivation in different countries were molecularly typed by means of MultiLocus Sequence Typing (MLST), using acnB, gapA, gyrB and rpoD gene fragments. A total of 2.5 kilobases was used to infer the phylogenetic relationship among the strains and possible recombination events. Haplotype diversity, linkage disequilibrium analysis, selection tests, gene flow estimates and codon adaptation index were also assessed. The dendrograms built by maximum likelihood with concatenated nucleotide and amino acid sequences revealed two major and two minor phylotypes. The same haplotype was found in strains originating from different continents, and different haplotypes were found in strains isolated in the same year from the same location. A recombination breakpoint was detected within the rpoD gene fragment. At the pathovar level, the Xaj populations studied here are clonal and under neutral selection. However, four Xaj strains isolated from walnut fruits with apical necrosis are under diversifying selection, suggesting a possible new adaptation. Gene flow estimates do not support the hypothesis of geographic isolation of the strains, even though the genetic diversity between the strains increases as the geographic distance between them increases. A triplet deletion, causing the absence of valine, was found in the rpoD fragment of all 45 Xaj strains when compared with X. axonopodis pv. citri strain 306. The codon adaptation index was high in all four genes studied, indicating a relevant metabolic activity.

Abstract: Form and function of mycorrhizas as well as tracing the presence of the mycorrhizal fungi through the geological time scale are herein first addressed. Then mycorrhizas and plant fitness, succession, mycorrhizas and ecosystem function, and mycorrhizal resiliency are introduced. From this, four hypotheses are drawn: (1) mycorrhizal diversity evolved in response to changes in Global Climate Change (GCC) environmental drivers, (2) mycorrhizal diversity will be modified by present changes in GCC environmental drivers, (3) mycorrhizal changes in response to ecological drivers of GCC will in turn modify plant, community, and ecosystem responses to the same, and (4) Mycorrhizas will continue to evolve in response to present and future changes in GCC factors. The drivers of climate change examined here are: CO₂ enrichment, temperature rise, altered precipitation, increased N-deposition, habitat fragmentation, and biotic invasion increase. These impact the soil-rhizosphere, plant and fungal physiology and/or ecosystem(s) directly and indirectly. Direct effects include changes in resource availability and change in distribution of mycorrhizas. Indirect effects include changes in below ground allocation of C to roots and changes in plant species distribution. GCC ecological drivers have been partitioned into four putative time frames: (1) Immediate (1–2 years) impacts, associated with ecosystem fragmentation and habitat loss realized through loss of plant-hosts and disturbance of the soil; (2) Short-term (3–10 year) impacts, resultant of biotic invasions of exotic mycorrhizal fungi, plants and pests, diseases and other abiotic perturbations; (3) Intermediate-term (11–20 year) impacts, of cumulative and additive effects of increased N (and S) deposition, soil acidification and other pollutants; and (4) Long-term (21–50+ year) impacts, where increased temperatures and CO₂ will destabilize global rainfall patterns, soil properties and plant ecosystem resilience. Due to dependence on their host for C-supply, orchid mycorrhizas and all heterotrophic mycorrhizal groups will be immediately impacted through loss of habitat and plant-hosts. Ectomycorrhizal (ECM) associations will be the principal group subject to short-term impacts, along with Ericoid mycorrhizas occurring in high altitude or high latitude ecosystems. This is due to susceptibility (low buffer capacity of soils) of many of the ECM systems and that GCC is accentuated at high latitudes and altitudes. Vulnerable mycorrhizal types subject to intermediate-term GCC changes include highly specialized ECM species associated with forest ecosystems and finally arbuscular mycorrhizas (AM) associated with grassland ecosystems. Although the soils of grasslands are generally well buffered, the soils of arid lands are highly buffered and will resist even fairly long term GCC impacts, and thus these arid, largely AM systems will be the least affect by GCC. Once there are major perturbations to the global hydrological cycle that change rainfall patterns and seasonal distributions, no aspect of the global mycorrhizal diversity will remain unaffected.

Abstract: Coprinoid mushrooms grown on wood of broad-leaf species were collected for the first time in Armenia and dikaryotic mycelial cultures were established. ITS (internal transcribed spacer) sequences identified one species as Coprinopsis strossmayeri and the other as a species closely related to Coprinellus radians. Mycelial growth and morphological features on different media are described. The pearl-white-silky colonies of C. strossmayeri are characterized by mycelial strands and by a light-yellow agar colorization. The species forms chlamydospores intercalary in its hyphae. Some hyphal ends form hyphal loops. Colonies of C. aff. radians have a characteristic yellow pigmentation and stain the agar yellowish. Hyphae are mostly clampless but at some septa, pseudoclamps are seen from which side-branches develop growing along the parental hyphae. In the mycelium of C. aff. radians, hyphal loops, hyphal swellings, cystidia and typical allocysts were observed. Both new species from Armenia show growth optima at temperatures of 25 to 30 °C and pHs of 6.0 to 7.0. Both grow in alkaline conditions up to pH 12.0 but not at pHs 3.0 and 4.0, classifying them with other coprinoid mushrooms as “ammonia fungi”. Both species grew on a variety of lignocellulosic substrates and both show polyphenol oxidase activities.