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The Book Reviews section of this issue (Mycological
Research106(10): 1247–1248, October 2002) includes
an appraisal of Dick's Straminipilous Fungi (Dick
2001). This seminal work synthesises the state of our
knowledge of the Peronosporomycetes (syn. Oomycetes),
marine straminipilous protists, plasmodiophorids, and
similar organisms. It also introduces the new kingdom
name Straminipila M. W. Dick 2001 to be used in
preference to the earlier published kingdom name
Chromista Cavalier-Smith 1981. This step is taken
because it is the flagellar apparatus of the zoospores
(heterokont; one whiplash and one tinsel) that is the
critical diagnostic feature of the kingdom, not the
presence of pigmented organelles (i.e. chromophyte
endosymbionts). For this reason, the terms ‘stramenopilous’ and ‘straminipilous’ had already gained popularity in the literature during the last decade, although
the kingdom name has not been formally proposed.
More detailed information is given in the review, but
mycologists in general need to be aware of this change
and to adopt the name in their teaching and writing for
what used to be known as the chromistan fungi,
oomycete fungi, or pseudofungi.
Mycological Research News features : Straminipila, a new kingdom name for oomycete fungi; and Fungi from coral
This issue starts with a major review of fungal siderophores, and includes 12 other papers. Molecular papers address
phylogeny and (or) infraspecific variation in Alternaria spp. (associated with apple core rot), Botrytis cinerea, Fusarium
sp. (on lichens), Alternaria spp., Phaeoacremonium (including grapevine disease agent), Pycnoporus spp., and
Verticillium fungicola, and, further heavily melanized variants of Gaemannomyces graminis var. tritici. Cell-wall
polysaccharides show Cephalotheca to be polyphyletic in this feature.
Also investigated are the degradative properties of a lichenicolus Fusarium sp. zoospore and cyst membrance proteins
in Phytophthora nicotianae, and phosphatase activities of an arbuscular mycorhizal fungus.
Revisions including keys are presented for Lichenostigma subgen. Lichenogramma (Arthoniales) and the British
species of Tazzetta (Pezizales).
The following new scientific names are introduced: Lichenostigma diploiciae, L. epipolina, L. gracilis, L. rouxii and L.
subradians spp. nov.; and Tazzetta scotica (syn. Pustularia scotica) comb. nov.
In April, Mycological Research News drew attention to
two studies on the fungi isolated from coral reefs
(Mycological Research106(4): 387, April 2002). Both
found that fungi generally encountered in terrestrial
environments predominated, and that while numerous
isolates could be obtained, the number of species
present was somewhat limited. It is always easier to
discover something than to find if it has been discovered
before. In this case, neither paper mentioned a
fascinating study by Kendrick et al. (1982) which
investigated fungi from the interior or living corals with
a view to identifying ones that might be involved in
their bioerosion. These authors discovered 18 species,
again mainly from ‘terrestrial’ genera such as Aspergillus, Cladopsorium, and Penicilliu. Further, they
demonstrated the presence of microborings attributed
to fungal hyphae in the aragonite coral skeletons by
light and scanning electron microscopy following plastic
infiltration; that the borings were of fungal origin was
confirmed by reinoculating samples of the coral
Siderastrea siderea with A. versicolor and P. stoloniferum
and reproducing the phenomenon in the laboratory.
The extent to which such fungi are involved in coral
declines, either as causal agents or secondary invaders
appears to be a fascinating area for further study,
particularly as bacteria rather than fungi have received
most attention in relation to coral reef health (Santavy
Siderophores are low molecular weight, iron-chelating ligands produced by nearly all microorganisms. Fungi synthesize a wide range of hydroxamate siderophores. This review considers the chemical and biological aspects of these siderophores, their distribution amongst fungal genera and their possible applications. Siderophores function primarily as iron transport compounds. Expression of siderophore biosynthesis and the uptake systems is regulated by internal iron concentrations. Transport of siderophores is an energy-dependent process and is stereoselective, depending on recognition of the metal ion coordination geometry. In addition to transporting iron, siderophores have other functions and effects, including enhancing pathogenicity, acting as intracellular iron storage compounds and suppressing growth of other microorganisms. Siderophores can complex other metals apart from iron, in particular the actinides. Because of their metal-binding ability there are potential applications for siderophores in medicine, reprocessing of nuclear fuel, remediation of metal-contaminated sites and the treatment of industrial waste.
Restrictions patterns of the ITS rDNA and a partial fragment of the β-tubulin gene were shown to help identify Phaeoacremonium species associated with diseased grapevines. PCR-RFLP markers revealed a high frequency of P. parasiticum, together with P. aleophilum, in fungi isolated from stems and trunks of mature diseased vines showing ‘hoja de malvón’ disease, and from young declining plants in Argentina. This distribution is different from that in vineyards in other parts of the world, where P. aleophilum is dominant. Indeed, this is the first report associating P. parasiticum with diseased vines.
Dry core rot of apple (DCR) and Alternaria black rot of citrus (ABR) have in the past respectively been ascribed to Alternaria alternata and A. citri. In recent years, however, it has been speculated that several other species of Alternaria could also be associated with these diseases. In an attempt to elucidate the identity of these taxa, 25 isolates associated with DCR, and 26 isolates associated with ABR were selected for molecular characterisation. Nucleotide sequences of 1116 sites including the histone gene section and the internal transcribed spacers (ITS 1 and 2) of the rRNA gene were determined for these isolates. The gene trees generated from the individual and combined data sets using maximum parsimony, maximum likelihood and neighbour-joining analysis methods distinguished five clades with strong bootstrap support, namely Alternaria sp., A. arborescens, A. infectoria, A. tenuissima, and a clade containing isolates variable in morphology, referred to as the Alternaria group. In the alignment of the combined ITS and histone data set, unique transition/transversion substitutions, as well as positional insertions and deletions were observed for each of the above clades. In addition, key sequences in the form of serial composing nucleotides in both the ITS and histone sections of the alignment were also discovered for the molecular identification of A. arborescens, A. infectoria and A. tenuissima. The final phylogeny also indicated that no host specificity existed among the species associated with these two post-harvest disease complexes. Contrary to the host specificity observed on leaf diseases of these hosts in the field, it appears that the post-harvest diseases are the result of adverse storage conditions and opportunism of different small-spored Alternaria spp.
The objectives of this study were to examine genetic variation, physiological dissimilarities and diversity in pathogenicity between Verticillium fungicola var. aleophilum and var. fungicola and within a population of six V. fungicola var. fungicola strains responsible for dry bubble outbreaks on mushroom farms. Genetic variability was investigated using random amplification of polymorphic DNA (RAPD). Mycelial growth rate, extracellular enzyme production and susceptibility to hydrogen peroxide were used to examine physiological dissimilarities. Variation in pathogenicity was studied both in vitro and during mushroom cultivation. All the physiological properties studied indicated that var. aleophilum isolates were potentially more efficient than var. fungicola isolates for rapid colonisation of the mushroom cultivation medium. They could then interact more efficiently with Agaricus bisporus to produce dry bubble disease. RAPD analysis confirmed that all the French isolates belonged to var. fungicola, and two isolates were distinguishable from the homogeneous group constituted by the others. These isolates had a higher mycelial growth rate and lower extracellular enzyme activities in liquid media, except for chitinases. Their spores were more susceptible to germination inhibition by hydrogen peroxide, and they were responsible for higher levels of affected mushrooms. The two varieties might be regarded as pathotypes that are geographically isolated, and variation in isolates of var. fungicola might have consequence for mushroom growers.
Botrytis cinerea (anamorph of Botryotinia fuckeliana) is a filamentous ascomycete that causes grey mould especially on grapevine. Based on the presence or the absence of two transposable elements (Boty and Flipper) two sibling sympatric populations named transposa and vacuma have been described. Among the vacuma population, some strains (designated HydR1) were found to be resistant to fenhexamid (a sterol C-4 demethylase inhibitor) and to show an increased sensitivity to 14α-demethylase inhibitors (DMIs). In order to assess whether or not mutations at the target gene level (CYP51) could underlie increased sensitivity to DMIs in HydR1 strains, we cloned the CYP51 gene and determined its DNA sequence in various B. cinerea strains. The gene was highly polymorphic, with mutations detected at 58 positions in the 35 strains analysed. The polymorphisms did not discriminate between transposa and vacuma strains, but did distinguish between HydR1 and non-HydR1 ones. Two expressed mutations were present in all HydR1 strains, namely phenylalanine to leucine at position 15 of the inferred protein, and serine to asparagine at position 105. These data, combined with the existence of morphological differences and somatic incompatibility between HydR1 and non-HydR1 strains, suggest that these two groups comprise distinct genetic entities.
Gaeumannomyces graminis var. tritici is the aetiologic agent of take-all disease of wheat and barley. Heavily-melanized variants of a lightly pigmented, virulent wild-type strain were isolated and characterized. These variants were phenotypically similar to Phialophora sp., the proposed anamorph of Gaeumannomyces graminis var. tritici. Unlike the wild-type G. graminis strain, Phialophora-like variants produced conidia and lost their ability to reproduce sexually after serial transfer. Some ascospores from initial self-crosses of the Phialophora-like variants regained the G. graminis phenotype, and these derivatives could again produce Phialophora-like variants. As with Phialophora isolates from the field, Phialophora-like variants produced in this study were non-pathogenic and produced less extracellular protein.
The cell wall alkali-extractable water-soluble polysaccharide (F1SS) purified from the three species of Cephalotheca has been characterized. Two different structures have been deduced by chemical and structural analyses. The structure of the polysaccharide F1SS from C. purpurea and C. reniformis is similar, and composed of 3,6-di-O-substituted mannopyranose with terminal residues of rhamnopyranose. The polysaccharide F1SS from C. sulfurea contains 2,6-di-O-substituted mannopyranose and terminal residues of galactofuranose. Our results confirm the relatedness of C. purpurea and C. reniformis with Ophiostomatales and of C. sulfurea with Sordariales.
The production of laccase, an enzyme of industrial interest, was screened among species of the genus Pycnoporus, in particular P. sanguineus. Strains were isolated from various tropical Chinese environments and phylogenetically compared to ones deposited in international collections. Molecular clustering, based on ribosomal ITS1-5.8S-ITS2 genomic sequence analysis, showed that the Chinese strains of P. sanguineus formed an homogeneous phylogenetic group distinguished by its laccase-overproducing character. The dikaryotic strain P. sanguineus G05 was selected for its ability to produce up to 40 000 U l−1 laccase in the presence of 2,5-xylidine, Tween 80 and maize bran. Since fruit bodies of P. sanguineus could be formed in the laboratory, monokaryotic laccase-hyperproducing strains were isolated using classic genetical methods. Among these isolates, strain G05.10 synthesized up to 71 000 U l−1 laccase, with a productivity of 5069 U l−1 d−1. The laccase was purified and identified as a 70 kDa protein with an acidic pI, and was very stable at high temperatures.
We compared the degradative enzymology of fusaria in a small clade of closely related species as determined by phylogenetic analysis of nuclear 28S rDNA sequences. The clade includes entomogenous species and at least one recently discovered lichenicolous species. The lichenicolous Fusarium sp. and three entomogenous species were tested for the ability to degrade lichen tissue in both the presence and the absence of antibiotic secondary compounds. Only the undescribed lichenicolous Fusarium sp. showed degradative ability irrespective of lichen secondary chemistry and this was correlated with its ability to hydrolyse enzymatically the antibiotic depside, lecanoric acid. Similarly, the lichenicolous Fusarium sp. exhibited the greatest capacity for degrading lichen cell walls and the highest levels of cell wall-degrading polysaccharidases. These results correlate the ability to exploit lichen substrates with the production of specific enzyme activities able to overcome the chemical and physical barriers that characterize lichen hosts.
Motile zoospores of species of oomycetes encyst rapidly to form walled cysts that germinate and infect host plants. Differences in the protein composition of the plasma membrane and endomembranes of zoospores and cysts of the oomycete Phytophthora nicotianae have been explored by comparing patterns of polypeptides in one- and two-dimensional gels of microsomal fractions. Against a backdrop of common components, this comparison revealed that at least 53 proteins were specific to, or occurred preferentially in, the microsomal fraction of one spore type or the other. In addition, proteins common to zoospore and cyst plasma membranes were further investigated by immunocytochemical labelling with a panel of 10 monoclonal antibodies raised against P. nicotianae spore components. The results of immunolocalisation studies and immunoblotting showed that the antibodies reacted with four different sets of membrane proteins, and were grouped accordingly. Group 1 antibodies bound preferentially to the bladder of the water expulsion vacuole or a region of the cell surface associated with it. Group 2 antibodies reacted with a protein of high relative molecular weight (>200 kDa) found in zoospores and cyst plasma membranes and in the cleavage membranes of sporangia. Group 3 antibodies reacted with a set of proteins occurring in the plasma membrane of zoospores and cysts, in the peripheral cisternae, in the spongiome membranes of the water expulsion vacuole, in the cleavage membranes of sporangia, and in the plasma membrane and apical vesicle membranes in hyphae and germinating cysts. Group 4 antibodies bound to a set of proteins present in the zoospore and cyst plasma membrane, in sporangial cleavage membranes and in the spongiome but not present in the peripheral cisternae, hyphae or germinating cysts. The results document the presence of proteins that are common to the plasma membrane of all stages of the asexual life cycle of P. nicotianae, of proteins that occur in the plasma membrane of the asexual spores but not of hyphae, and of proteins that occur in the membranes of either zoospores or cysts. The results also indicate that zoospore and cyst plasma membrane proteins may be present in specific subsets of other membranes within the zoospores.
We investigated the influence of changes in external phosphorus (P) concentration on the proportion of phosphatase-active structures of the arbuscular mycorrhizal fungus Gigaspora margarita associated with Allium cepa. The P treatment was started when mycorrhizal colonisation had been established, and plant systems were harvested three times after the start of the P treatment. Higher shoot dry weights and P contents were observed in the high-P treated plants at the last harvest. We did not find any change in the proportion of phosphatase-active extraradical mycelium following P treatment. However, the proportion of alkaline phosphatase-active mycelium was positively correlated for extraradical and intraradical mycelium. Also, the proportion of alkaline phosphatase-active arbuscules seemed to increase with the shoot fresh weight, whereas the proportion of acid phosphatase-active arbuscules decreased with higher shoot P concentration and dry weight. We have shown experimentally that the intraradical mycelium of G. margarita, but not the extraradical mycelium, responds metabolically to plant P concentration, and possibly also to external P availability.
A synopsis of the subgenus of lichenicolous fungi Lichenogramma is presented. It comprises eight species of Lichenostigma with oval to elongate ascomata connected to superficial strands of vegetative hyphae. Five of them are described here as new: Lichenostigma diploiciae (on Diploicia subcanescens); L. epipolina (on Diplotomma epipolium); L. gracilis (on Acarospora fuscata); L. rouxii (on Squamarina spp.); and L. subradians (on Acarospora spp., mainly subgen. Acarospora). The concept of the genus Lichenostigma is enlarged to accommodate also species with submuriform ascospores. A key to all the species of the subgenus is provided.
Notes on the nomenclature and taxonomy of British species recorded in the genus Tazzetta, and in its synonym Pustularia, are presented. The new combination T. scotica is proposed, with a neotype designated. Four species are recognised as British, and a key for their identification provided.