Diversity of arbuscular mycorrhizal fungi colonising roots of the grass species<Emphasis Type="Italic"> Agrostis capillaris</Emphasis> and<Emphasis Type="Italic"> Lolium perenne</Emphasis> in a field experiment

Analysis of arbuscular mycorrhizal (AM) fungal diversity through morphological characters of spores and intraradicular hyphae has suggested previously that preferential associations occur between plants and AM fungi. A field experiment was established to investigate whether AM fungal diversity is affected by different host plants in upland grasslands. Indigenous vegetation from plots in an unimproved pasture was replaced with monocultures of either Agrostis capillaris or Lolium perenne. Modification of the diversity of AM fungi in these plots was evaluated by analysis of partial sequences in the large subunit (LSU) ribosomal RNA (rDNA) genes. General primers for AM fungi were designed for the PCR amplification of partial sequences using DNA extracted from root tissues of A. capillaris and L. perenne. PCR products were used to construct LSU rDNA libraries. Sequencing of randomly selected clones indicated that plant roots were colonised by AM fungi belonging to the genera Glomus, Acaulospora and Scutellospora. There was a difference in the diversity of AM fungi colonising roots of A. capillaris and L. perenne that was confirmed by PCR using primers specific for each sequence group. These molecular data suggest the existence of a selection pressure of plants on AM fungal communities.     

Genetic covariation of the marine fungal symbiont Haloguignardia irritans (Ascomycota, Pezizomycotina) with its algal hosts Cystoseira and Halidrys (Phaeophyceae, Fucales) along the west coast of North America

The fungal endophyte Haloguignardia irritans induces gall formation on the brown algal genera Cystoseira and Halidrys occurring from Oregon to Baja California, Mexico. Here we examine genetic covariation and compare rDNA phylogenies to investigate the coevolutionary histories of H. irritans and its algal hosts. Despite recognition of H. irritans as a single morphological species, internal transcribed spacer rDNA sequences representative of its geographic range are characterized by sequence variation at the intraspecific to intrageneric levels. An assessment of parallel cladogenesis between endophyte and host phylogenies provides evidence for a combination of independent fungal divergence and host jumping, similar to that observed in terrestrial lichens. Our results suggest that reduced gene flow due to geographic isolation is a major contributing factor to more concerted covariation observed at one island site, rather than to differences among algal host species alone. Because geography and its effects on gene flow can create heterogeneous mosaics of coevolution for symbioses in terrestrial environments, our results support the notion that conservation efforts toward the maintenance of genetic diversity in marine environments should likewise consider geographic complexity and its effects on coevolving marine species.     

Estimating and comparing the diversity of marine actinobacteria

This paper reviews the application of species richness estimators to microbial diversity data and describes phylogenetic approaches to comparing microbial communities. The techniques are demonstrated using a community of marine actinobacteria. Results demonstrate that marine environments harbour massive actinobacterial diversity. Furthermore, these predictions are likely to be severe underestimates due to the use of arbitrary OTU definitions.     

Identification,molecular characterization,and evolution of group I introns at the expansion segment D11 of 28S rDNA in Rhizoctonia species

The nuclear ribosomal DNA of Rhizoctonia species is polymorphic in terms of the nucleotide composition and length. Insertions of 349–410 nucleotides in length with characteristics of group I introns were detected at a single insertion point at the expansion segment D11 of 28S rDNA in 12 out of 64 isolates. Eleven corresponded to Rhizoctonia solani (teleomorph: Thanatephorous) and one (AG-Q) to Rhizoctonia spp. (teleomorph: Ceratobasidium). Sequence data showed that all but AG-Q contained conserved DNA catalytic core regions (P, Q, R, and S) essential for selfsplicing. The predicted secondary structure revealed that base-paired helices corresponded to subgroup IC1. Isolates from same anastomosis group and even subgroups within R. solani were variable with regard to possession of introns. Phylogenetic analyses indicated that introns were vertically transmitted. Unfortunately, sequence data from the conserved region from all 64 isolates were not useful for delimiting species. Analyses with IC1 introns at same insertion point, of both Ascomycota and Basidiomycota indicated the possibility of horizontal transfer at this site. The present study uncovered new questions on evolutionary pattern of change of these introns within Rhizoctonia species.     

Morphology and molecular phylogeny of Nitzschia bizertensis sp. nov.—A new domoic acid-producer

A new toxin-producing marine diatom, Nitzschia bizertensis sp. nov., isolated from the Bizerte Lagoon (Tunisia, Southwest Mediterranean Sea) is, based on studies on eight different strains, characterized morphologically by light microscopy, transmission and scanning electron microscopy, and phylogenetically using the nuclear rDNA regions: SSU, ITS1, 5.8S, ITS2 and D1–D3 of the LSU. The species belongs to the sections Lanceolatae or Lineares as defined by Cleve and Grunow (1880). These sections are characterized by species having linear-lanceolate valves with an eccentric raphe where the fibulae does not extend into the valve, and are otherwise famous for the lack of characters useful for delineation of species. Nitzschia bizertensis differs from most other species in these sections by having a high density of interstriae. The morphological and phylogenetic studies and comparisons with previously described Nitzschia species showed Nitzschia bizertensis sp. nov. to be a new species. Batch culture experiments were conducted for estimations of maximum growth rate and production of domoic acid (DA). Maximum cellular DA content of the examined strains ranged from 2 × 10⁻⁴ to 3.6 × 10⁻² pg cells⁻¹. The total DA concentration (pg mL⁻¹) was high already in exponential growth phase maybe due to reinoculation of “old” stationary phase cells, and increased into stationary growth phase where it reached a stationary level varying among the strains from ca. 4500 to 9500 pg mL⁻¹. Nitzschia bizertensis represents a new domoic acid-producing diatom and is the second toxin producing Nitzschia species. The resolution of Nitzschia bizertensis and Nitzschia navis-varingica in different parts of the LSU phylogenetic tree, and the recovery of the Pseudo-nitzschia species phylogenetically distant from those two species suggests that the ability to produce DA either evolved multiple times independently or was lost multiple times.     

青藏高原食草动物粪栖真菌的多样性

分别利用真菌通用引物和厌氧真菌特异引物构建了西藏地区3种反刍动物和1种单胃动物共8份新鲜粪样的ITS克隆文库,以通过系统发育分析解析其中好氧真菌与厌氧真菌的多样性。通用引物ITS文库测得324条真菌序列,分别属于子囊菌门Ascomycota 3个目、担子菌门Basidiomycota 2个目、接合菌门Zygomycota的1个目和严格厌氧的新丽鞭毛菌门Neocallimastigomycota,共24个OTUs。其中,子囊菌门相对丰度最高,占80.6%;新丽鞭毛菌门相对丰度最低,仅占0.6%。大部分OTUs与已知真菌属、种关系较远。厌氧真菌特异引物文库测得661条序列,全部属于新丽鞭毛菌门,包括所有已知的厌氧霉属Anaeromyces、盲肠菌属Caecomyces、肠霉属Cyllamyces、新丽鞭毛属Neocallimastix、奥式霉属Orpinomyces、胃梨囊霉属Piromyces 6个属和3个未培养的属级类群(NG9、NG10、NG11),共29个OTUs。其中3个已知的单中心属存在于所有反刍动物样品中,并以Piromyces相对丰度最高(37.4%)。单胃动物马粪样中全部为NG9类群。NG9是本研究新发现的属级类群,研究中同时揭示有多个未培养种和潜在的新种。研究结果证明青藏高原反刍动物粪栖真菌多样性较高,并存在丰富的未培养种和潜在的新属及新种。     

Three new asexual arthroconidial yeasts, Geotrichum carabidarum sp. nov., Geotrichum histeridarum sp. nov., and Geotrichum cucujoidarum sp. nov., isolated from the gut of insects

Twenty arthroconidial yeasts were isolated from the digestive tract of basidiome-feeding beetles and lepidopteran larvae. All of the yeasts reproduced only asexually by arthroconidia and some by endo- or blastoconidia as well. Based on the comparisons of sequences in ribosomal RNA genes and other taxonomic characteristics, the yeasts were identified as three unknown Geotrichum species. The three new species are described as Geotrichum carabidarum (NRRL Y-27727^T), G. histeridarum (NRRL Y-27729^T), and G. cucujoidarum (NRRL Y-27731^T). Phylogenetic analyses from ribosomal DNA sequences showed that members of the genus Geotrichum and related arthroconidial yeast taxa were divided into two major clades: (1) Dipodascus and Galactomyces with Geotrichum anamorphs including all the new species; and (2) Magnusiomyces with Saprochaete anamorphs. G. cucujoidarum formed a subclade with G. fermentans and Geotrichum sp. Y-5419, while the two closely related species, G. carabidarum and G. histeridarum, represent a new basal subclade in the clade of Geotrichum and its teleomorphs.