Isolation of a homothallic mutant in <Emphasis Type="Italic">Lentinula edodes</Emphasis>

To obtain a homothallic mutant in Lentinula edodes, basidiospores derived from the common Bmut dikaryon (A1B1mut × A2B1mut) were treated with UV irradiation. Of a total of approximately 5000 monosporous cultures recovered, a single basidiospore isolate was found to produce the hyphae bearing clamp connections without mating. This mutant strain could form fruit bodies, and all its single basidiospore isolates developed into colonies with clamp connections. Such homothallic behaviors were transmitted from the mutant strain to the next generation. During the germination and following hyphal elongation in a single basidiospore of mutant strain, clamp connections were clearly detected in multicellular hyphae, which contained two nuclei in each cell. Their clamp connections were morphologically variable, viz., pseudo, abnormal, and true clamps. Amplified fragment length polymorphism (AFLP) profiles among the basidiospore isolates of mutant strain were identical, indicating that the mutant strain produced isogenic basidiospore progeny. Contribution no. 385 from the Tottori Mycological Institute     

Enviromentally Induced Changes in Clamp Connection Incidence in Hyphal Branching Systems of Coprinus disseminatus

The incidence of clamp connections among surface hyphae at thecolony margin of apparent dikaryons from four stocks of Coprinusdisseminatus has been investigated under several environmentalconditions. On 2 per cent malt agar, clamp connections are formed at allnodes of the main leader hyphae, but they are absent from theearlier-formed nodes of primary branch hyphae. Most primarybranches have begun to form clamp connections by their fifthcell division, and continue to do so subsequently. Onset ofclamp connection formation in primary branches is delayed whenthe concentration of malt in the medium is reduced. The occurrenceof clamp connections on main leader hyphae is reduced or preventedwhen nutrient supply in the medium is reduced, or when the mediumis ‘pre-staled’ by previous growth of C. disseminatus.Clamp-free main hyphal tips revert to formation of clamp connectionswhen the intact hyphal system is transferred to more favourableenvironmental conditions. Presence of clamp connections on bothmain and branch hyphae is associated with high hyphal diameter,and in some instances, also with high hyphal extension rate. The significance of these observations to mechanisms of growthof hyphal branching systems and their relevance to other speciesthat form clamp connections intermittently, are discussed.     

Light and electron microscope study of unilateral mating between a secondary mutant and a wild-type strain ofSchizophyllum commune

Summary After hyphal fusions between the secondary mutant and wild-type strains ofSchizophyllum commune some of the fused hyphae show several nuclei per cell and dissolved septa. These hyphae are designated migration hyphae because they are evidently the main routes of nuclear exchange between the two strains. On the wild-type side of the mating the nuclei spread gradually from the main part of the migration hyphae into the side branches, which develop into an extensive network with many anastomoses. The first cells with pseudoclamps or clamp connections are observed in this network.On the mutant side of the mating the branching is less developed and the number of anastomoses is smaller. The cross walls of the septa are poorly dissolved, and nuclear aggregations occur in the hyphae. No development of clamp connections or pseudoclamps is observed. It is suggested that the unilateral mating response of the secondary mutant strain might possibly be caused by the failure of the septa in the mutant hyphae to dissolve, which inhibits the distribution of the nuclei into the side branches of migration hyphae.     

Septins enforce morphogenetic events during sexual reproduction and contribute to virulence of Cryptococcus neoformans

Septins are conserved, cytoskeletal GTPases that contribute to cytokinesis, exocytosis, cell surface organization and vesicle fusion by mechanisms that are poorly understood. Roles of septins in morphogenesis and virulence of a human pathogen and basidiomycetous yeast Cryptococcus neoformans were investigated. In contrast to a well‐established paradigm in S. cerevisiae, Cdc3 and Cdc12 septin homologues are dispensable for growth in C. neoformans yeast cells at 24°C but are essential at 37°C. In a bilateral cross between septin mutants, cells fuse but the resulting hyphae exhibit morphological abnormalities, including lack of properly fused specialized clamp cells and failure to produce spores. Interestingly, post‐mating hyphae of the septin mutants have a defect in nuclear distribution. Thus, septins are essential for the development of spores, clamp cell fusion and also play a specific role in nuclear dynamics in hyphae. In the post‐mating hyphae the septins localize to discrete sites in clamp connections, to the septa and the bases of the initial emerging spores. Strains lacking CDC3 or CDC12 exhibit significantly reduced virulence in a Galleria mellonella model of infection. Thus, C. neoformans septins are vital to morphology of the hyphae and contribute to virulence.     

Direct microscopic studies of clamp connection formation in growing hyphae of Schizophyllum commune

Summary Photomicroscopic studies of clamp connection formation were collated with microscopic measurements of apical extension and mitosis in rapidly growing dikaryotic hyphae of Schizophyllum commune. Intercalary clamp connection formation was described in sub-terminal regions of the dikaryon. Conventional (i.e., rearward) clamp initiation was compared to forward clamp connection formation. Primary branch emergence was observed from clamp connections in growing hyphae and contrasted to sub-basidial branching in the hymenium of dikaryotic fruit-bodies.     

Multinucleate nature,and mating by use of isozyme analysis inPoria cocos

Double staining study of nuclei and cell walls inPoria cocos indicated that the hyphal cells were multinucleate and had no clamp connections. Isozyme analysis of alcohol dehydrogenase (ADH) in 52 natural isolates revealed that there were three types of banding patterns: type I, five bands; type II, one slow band; type III, one fast band. Regenerants expressing type-II or type-III ADH-isozyme pattern were obtained from type-I isolates via protoplast manipulation. When the type-II regenerants were mated with the type-III regenerants, hyphae of type-I phenotype appeared. These data indicated that these type-II and type-III regenerants derived from protoplasts of the type-I isolates were primary hyphae. These primary hyphal cells were also multinucleate. Inter-strain mating ofP. cocos was performed and confirmed by ADH-isozyme analysis. Confronting cultures of a type-III regenerant derived from protoplasts of a type-I isolate and a type-II regenerant derived from a type-II isolate resulted in type-I hyphae.     

Curved fossil bee cells as tools for reconstructing the evolutionary history and palaeogeographical distribution of Diphaglossinae (Apoidea,Colletidae)

The new ichnospecies Celliforma curvata is described to include curved fossil bee cells from Argentina, Uruguay and the USA. The upper part of the cell (neck) of the new ichnospecies is curved, and accordingly, it can be attributed to bees of the subfamily Diphaglossinae (Colletidae). The oldest record of C. curvata, from the early Eocene of North America (52–49 Ma), provides a minimum age for the appearance of this subfamily, in accordance with an already proposed calibrated phylogeny. It is also proposed that these fossil cells could be used for future calibrations of molecular clocks. C. curvata indicates that Diphaglossinae had a widespread distribution, from southern Utah to extra‐Andean Patagonia at 42°S. In contrast, extant representatives reach only 38°S in this region. Diphaglossinae were more extended southwards in the past thanks to better environmental conditions in extra‐Andean Patagonia.     

Direct studies of dikaryotization in Schizophyllum commune

The growth, duplication and fate of multikaryotic hyphae bearing true clamp connections, as derived from compatible matings of Schizophyllum commune, were studied by phase contrast microscopy. The nuclei (N) of multikaryotic apices maintained a near central position during hyphal growth. True clamp connection formation occurred with near synchronous mitosis followed by septal synthesis across the clamp neck and main hyphal axis. Nuclear progeny after mitosis in a hexakaryon included 6 N in the apex, 1 N in the clamp and 5 N in the penultimate cell; the solitary nucleus in the clamp later entered the penultimate cell. Similar events occurred for clamp connection formation and mitosis in the trikaryon, quadrikaryon or pentakaryon, whether in the apex or primary branches. Nuclear content of the multikaryotic apex (2 N through 10 N) had no apparent effect on the rate of individual hyphal growth. Reduction of the nuclear number in a trikaryon occurred by long-term entrappment of a solitary nucleus in the clamp and subsequent outgrowth of the dikaryotic penultimate cell. Occasionally, more than one nucleus became entrapped in the clamp cell. The ephemeral nature of the multikaryon was indicated by the fact that older cultures appeared to be exclusively dikaryotic hyphae at the colony periphery.     

A new Eocene fossil of the genus Phycopeltis (Ulvophyceae,Chlorophyta)

A fossil of the aerophytic green algal genus Phycopeltis (Trentepohliaes, Ulvophyceae) dated to 35 Ma, is reported from the Pikopiko Fossil Forest, Southland, New Zealand. Previous reports of fossilized Phycopeltis have been subsequently synonymized with fungi by other authors; however, our specimen is not vulnerable to their criticisms. Inflated cells present in two approximately concentric rings are interpreted as gametangia, with irregular structures resembling the gametangial pores of modern material; sporophytic material is absent. The fossil resembles the modern disc‐forming species P. novae‐zelandiae, P. expansa, and P. arundinacea. The limited material available prevents the assignation of a specific epithet, but the habit and dimensions of the fossil clearly fall within those of modern representatives of the genus. Its single cell thickness throughout, absence of distinct melanization, and larger size demonstrate that it is not a fungal shield. The specimen constitutes arguably the most convincing fossil belonging to Trentepohliales, and the first unambiguously for the genus Phycopeltis. It is consistent in age with other known fossils of the order that, when combined with molecular evidence, suggests a terrestrial radiation far more recent than that of land plants.     

A discovery of riphean heterotrophs in the Lakhanda group of Siberia

New fossil remains have been discovered from the well-known Lakhanda Microbiota (1015–1025 Ma, Uchur-Maya Region, Southeastern Siberia). The microfossils have characters observed in microscopic fungi, such as a reticulate mycelium, formed by anastomizing hyphae of non-cellular structure and of variable width. The fungal mycelium shows that hyphae grew in a certain direction, both forwards and backwards. As their length increased, the hyphae became curved and merged with neighboring hyphae to form enclosed spaces. The presence on hyphae of knoblike trapping structures and secretion of adhesive enzymes suggest a similarity with modern nematophagous fungi. Microorganisms associated with the adhesive hyphae consist of colonial green unicellular algae and thin bacterial sheaths, which may indicate mutually beneficial relationships between morphologically and biologically different partners. Microfossils of fungal origin are systematically described. They include Aimonema ramosa gen. et sp. nov. and the green unicellular alga Eoprotoderma neruenica gen. et sp. nov., forming a symbiotic association.     

Athelia termitophila sp. nov. is the teleomorph of the termite ball fungus Fibularhizoctonia sp.

A new species of Athelia, A. termitophila, from Japan is described and illustrated on the basis of morphological and phylogenetic analyses. Basidiomes of this species are characterized by having hyphae sometimes with clamp connections at the septa, basidia without clamp connections at the basal septa, and ellipsoid to ovoid basidiospores measuring 4.5–6 × 3–4.5 μm. In culture, mycelia produce pale brown, orange-brown to brown, globose sclerotia measuring 0.24–0.41 mm diam. The sclerotia are distinctly different in shape and size from those of other Athelia species, and are occasionally found inside the woody substrate beneath basidiomes. They are identical in shape and size to those of Fibularhizoctonia sp., also known as termite balls. Phylogenetic analysis using internal transcribed spacer (ITS) sequence data revealed that A. termitophila is the teleomorph of Fibularhizoctonia sp.     

The structure and formation of host-parasite pit connections between the red algal alloparasiteHarveyella mirabilis and its red algal hostOdonthalia floccosa

Summary Harveyella mirabilis is a colourless red algal alloparasite which grows on and within its photosynthetic hostOdonthalia floccosa. Cells ofHarveyella establish secondary pit connections (PCs) with other parasite cells and with cells of the host. Small, uninucleate conjunctor cells are produced by parasite cells and remain connected to them by PCs. Conjunctor cells may fuse with either an adjacent host or parasite cell, with the parasite-conjunctor cell PC becoming either a host-parasite or parasite-parasite secondary PC. Occasionally the conjunctor cell does not fuse with an adjacent cell (either host or parasite) and degenerates. The secondary pit plug which forms between a parasite cell and its conjunctor cell always develops with two structurally distinct surfaces characteristic of a host-parasite pit plug. Only if the conjunctor cell fuses with another parasite cell will the structure of the pit plug be altered to that of a parasite-parasite pit plug. Fungal hyphae also invade the region of infection, andHarveyella cells respond by producing nonfunctional conjunctor cells that grow towards adjacent hyphae. Evidence suggests that secondary PCs may be induced to form mechanically, by the physical presence of another cell, rather than in direct response to a message received from an adjacent cell. The mechanism of secondary PC formation described here is similar to that reported for the closely related alloparasiteHolmsella and may be common to a number of red algal parasitic associations. Helen Margaret Quirk, B. Sc. (Hons), M. Sc. (1953–1982), student, research assistant and friend, died after a long illness on October 24, 1982.     

A new Sparassis species from Spain described using morphological and molecular data

Sparassis miniensis, collected in Pinus pinaster forests in Galicia (northwest Iberian Peninsula) is described as a new species, based on morphological and molecular data. Sparassis miniensis is morphologically distinct from all other species in the genus Sparassis based on scattered flabellae, which are strongly laciniated, azonate, and arise from an orange to rose-purplish base. The sporadic presence of clamp connections is restricted to subhymenial hyphae. Molecular data from LSU-rDNA, ITS and partial gene coding RNA polymerase subunit II (rpb2) suggest a close relationship between the new species S. miniensis and S. brevipes, another European species producing large fruiting bodies but with entire flabellae and no clamp connections.     

Long‐term evolutionary and ecological responses of calcifying phytoplankton to changes in atmospheric CO2

Calcifying phytoplankton play an important role in marine ecosystems and global biogeochemical cycles, affecting the transfer of both organic and inorganic carbon from the surface to the deep ocean. Coccolithophores are the most prominent members of this group, being well adapted to low‐nutrients environments (e.g., subtropical gyres). Despite urgent concerns, their response to rising atmospheric carbon dioxide levels (pCO₂) and ocean acidification is still poorly understood, and short‐term experiments may not extrapolate into longer‐term climatic adaptation. Current atmospheric pCO₂ (~390 ppmv) is unprecedented since at least 3 million years ago (Ma), and levels projected for the next century were last seen more than 34 Ma. Hence, a deep‐time perspective is needed to understand the long‐term effects of high pCO₂ on the biosphere. Here we combine a comprehensive fossil data set on coccolithophore cell size with a novel measure of ecological prominence: Summed Common Species Occurrence Rate (SCOR). The SCOR is decoupled from species richness, and captures changes in the extent to which coccolithophores were common and widespread, based on global occurrences in deep‐sea sediments. The size and SCOR records are compared to state‐of‐the‐art data on climatic and environmental changes from 50 to 5 Ma. We advance beyond simple correlations and trends to quantify the relative strength and directionality of information transfer among these records. Coccolithophores were globally more common and widespread, larger, and more heavily calcified in the pre‐34 Ma greenhouse world, and declined along with pCO₂ during the Oligocene (34–23 Ma). Our results suggest that atmospheric pCO₂ has exerted an important long‐term control on coccolithophores, directly through its availability for photosynthesis or indirectly via weathering supply of resources for growth and calcification.     

Nuclear and Non-nuclear Factors influencing Clamp Connection Formation in Coprinus disseminatus

Matings between sister single spore lines of Coprinus disseminatusshowed a cryptic tetrapolar pattern. The two groups of matingsthat resulted in formation of mycelia with clamp connections(apparent dikaryons) differed in rate of nuclear penetrationduring mating. In one group penetration occurred at rates comparablewith nuclear migration in other species and in the other groupit was often extensive but at a rate similar to, or less than,the dikaryon growth-rate. No differences were detected betweenthese two groups in stability, colony extension rate, frequencyof clamp connections, proportions of true clamp connectionsand pseudoclamps, or number of nuclei per hyphal tip cell. Cytological studies and the isolation of hyphal tips showedthat both groups of apparent dikaryons were heterokaryotic di-or trikaryons. The di- and trikaryotic conditions co-existedin the same mycelium, but adjacent cells of individual branchingsystems usually contained equal numbers of nuclei. Within apparentdikaryons the number and kinds of nuclei per cell were similarin hyphae with clamp connections and those with simple septa.Treatments that prevented clamp connection formation did notalter the nuclear status of most of the hyphae. Irregularities in nuclear distribution were infrequent and mostwere associated with pseudoclamps. Forty per cent of nodes withprobable pseudoclamps yielded homokaryotic branches, which wereof either constituent mating type. There was some indicationthat irregularities in nuclear distribution could also occurduring divisions associated with simple septa.     

Precambrian–Cambrian boundary interval occurrence and form of the enigmatic tubular body fossil Shaanxilithes ningqiangensis from the Lesser Himalaya of India

The affinity of the Ediacaran fossil Shaanxilithes ningqiangensis and putatively related forms has long been enigmatic; over the past few decades, interpretations ranging from trace fossils to algae to metazoans of uncertain phylogenetic placement have been proposed. Combined morphological and geochemical evidence from a new occurrence of S. ningqiangensis in the Krol and Tal groups of the Lesser Himalaya of India indicates that S. ningqiangensis is not a trace fossil, but rather an organic‐walled tubular body fossil of unknown taxonomic affinity. Specimens consist of compressed organic cylindrical structures, characterized by extended, overlapping or fragmented iterated units. Where specimens intersect, overlapping rather than branching or intraplanar crossing is observed. Lithologic comparisons and sequence stratigraphic data all suggest a late Ediacaran age for the uppermost Krol Group and basalmost Tal Group. By extending the biogeographical distribution of S. ningqiangensis, hitherto confined to the Ediacaran of China and potentially Siberia, to the Precambrian–Cambrian boundary interval of India, this new occurrence of S. ningqiangensis expands the biostratigraphic utility of this enigmatic fossil to the inter‐regional and intercontinental scale. Moreover, study of these new and exceptionally preserved samples may help to significantly constrain the long‐debated problem of Shaanxilithes' affinity, elucidating its ‘problematic’ status and shedding new light upon the ecology and taphonomy of one of the most significant intervals in early life history.     

Leucosporidium fellii sp. nov., a basidiomycetous yeast that degrades L(+)-tartaric acid

A new species of basidiomycetous yeast Leucosporidium fellii was isolated from soil in Portugal on a selective L(+)-tartaric acid medium. This yeast is self-sporulating but forms dikaryotic hyphae with clamp connections and is presumably homothallic. It differs from the type strain of Leucosporidium scottii in its life cycle, assimilation pattern and guanine-cytosine content and from the other described Leucosporidium species by additional characteristics.     

Ectomycorrhizal syntheses with Picea abies and three fungal species: a case study on the use of an in vitro technique to identify naturally occurring ectomycorrhizae

Ectomycorrhizal syntheses between Picea abies and the fungal associates Scleroderma citrinum, Boletus luridus, and Tricholoma vaccinum were carried out using Melin's Erlenmeyer flask technique. The symbioses of S. citrinum were characterized by a mantle composed of an outer prosenchymatous and an inner synenchymatous layer. The mantles of B. luridus and T. vaccinum were solely prosenchymatous. Rhizomorphs were produced in all treatments, but only in association with S. citrinum were they differentiated with additional, enlarged hyphae. All synthesized ectomycorrhizae were white or whitish to light orange and greyishorange. On large-scale root sampling in two differing Picea abies forests in Switzerland, nine out of a total of 22 morphological types of ectomycorrhizae were white or yellow in colour and were, therefore, comparable with the synthesized ectomycorrhizae. These nine natural types generally had distinct mantle features (irregular synenchyma, gelatinous matrix, cystides, thick-walled hyphae), but mostly lacked clamp connections. Synthesized ectomycorrhizae, on the other hand, lacked distinct mantle characteristics and always had clamp connections. Natural and synthesized white or yellow ectomycorrhizae did not coincide morphologically and thus identification of the fungal partners of natural symbioses by means of in vitro-synthesis with potential ectomycorrhizal fungi was not possible in the present study.     

Adeylithon bosencei gen. et sp. nov. (Corallinales,Rhodophyta): a new reef‐building genus with anatomical affinities with the fossil Aethesolithon

Adeylithon gen. nov. with one species, A. bosencei sp. nov., belonging to the subfamily Hydrolithoideae is described from Pacific coral reefs based on psbA sequences and morpho‐anatomy. In contrast with Hydrolithon, A. bosencei showed layers of large polygonal “cells,” which resulted from extensive lateral fusions of perithallial cells, interspersed among layers of vegetative cells. This anatomical feature is shared with the fossil Aethesolithon, but lacking DNA sequences from the fossils and the fragmentary nature of Aethesolithon type material, we cannot ascertain if Adeylithon and Aethesolithon are congeneric. Morpho‐anatomical features of A. bosencei were generally congruent with diagnostic features of the subfamily Hydrolithoideae: (i) outline of cell filaments entirely lost in large portions due to pervasive and extensive cell fusions, (ii) trichocytes not arranged in tightly packed horizontal fields, (iii) basal layer without palisade cells, and (iv) cells lining the canal pore oriented more or less perpendicular to roof surface and not protruding into the canal. However, it showed a predominant monomerous thallus organization and trichocytes were disposed in large pustulate, horizontal fields, although they were not tightly packed and did not become distinctly buried in the thallus. Only mature tetrasporangial conceptacles were observed, therefore the type of conceptacle roof formation remained undetermined. Adeylithon bosencei occurs on shallow coral reefs, in Australia, Papua New Guinea, and South Pacific islands (Fiji, Vanuatu). Fossil Aethesolithon is considered an important component of shallow coral reefs since the Miocene; fossil records showed a broad Indo‐Pacific distribution, but a long‐term process of range contraction in the last 2.6 million years, resulting in an overlap with the distribution of the extant Adeylithon. While the congeneric nature of extant and fossil taxa remained uncertain, similarities in morpho‐anatomy, habitat, and distribution may indicate that both taxa likely shared a common ancestor.     

Palaeomagnetic analysis of the Sterkfontein palaeocave deposits: implications for the age of the hominin fossils and stone tool industries

Palaeomagnetic analysis was conducted on speleothems from Members 1-5 at Sterkfontein Cave, South Africa. Palaeomagnetic analysis of siltstone and speleothem from the bulk of Member 4 indicate a reversed magnetic polarity that dates the deposits and its Australopithecus africanus fossils to between 2.58 and ∼2.16 Ma. Further confirmation of this age comes in the form of two short normal polarity events correlated to the Rèunion (∼2.16 Ma) and Huckleberry Ridge (∼2.05 Ma) events in speleothem capping the bulk of Member 4 and coeval with deposition of the final phase of Member 4, including A. africanus fossil Sts 5. At ∼2.16-2.05 Ma, Sts 5 is the youngest representative of A. africanus yet discovered. Palaeomagnetic analysis of the Silberberg Grotto deposits identifies a single short geomagnetic field event in flowstone overlying the StW 573 Australopithecus fossil, which is suggested to represent the Rèunion event at ∼2.16 Ma. This further supports the uranium lead age estimates of 2.3-2.2 Ma for the StW 573 fossil. Based on a reversed polarity for the deposits below the skeleton it cannot be older than 2.58 Ma. If StW 573 is considered to be a second species of Australopithecus then this indicates that two species of Australopithecus are present at Sterkfontein between 2.6 and 2.0 Ma. All of the Member 5 deposits date to less than 1.8 Ma based on a comparison of palaeomagnetic, faunal, and electron spin resonance age estimates. The StW 53 fossil bearing infill (M5A) is intermediate in age between Member 4 and the rest of Member 5 (B-C) at around 1.78-1.49 Ma. The rest of Member 5 (B-C) containing Oldowan and Acheulian stone tools and Homo and Paranthropus fossils was deposited gradually between 1.40 and 1.07 Ma, much younger than previously suggested.