Conidial Wall Research Articles

Erratum: Structure of chitin in the cell walls of newly formed and mature conidia of Fusarium sulphureum

Samples of 7-day-old septate conidia (mature conidia) and newly released aseptate ones (immature conidia) of Fusarium sulphureum were hydrolyzed successively in KOH, acetic acid – H2O2, and H2SO4. The cell wall residue of the mature conidia remained intact throughout the hydrolysis but that of immature conidia dissolved in the H2SO4. Thus, the immature conidial cell wall is substantially different from that of mature conidial cells or growing hyphae and the cell wall undergoes a structural transformation following conidium release from the conidiogenous cell. X-ray diffraction analyses of the wall residues following KOH and acetic acid – H2O2 hydrolysis showed that the mature conidial wall residue had a crystalline chitin component, while the residue of the immature conidial wall was more amorphous and had smaller crystals. An X-ray diffraction pattern of the dissolved immature conidial wall that was recovered from the H2SO4 hydrolysate showed that it contained crystalline chitin.Infrared spectroscopic an...

Fine structural studies of the Chrysosporium state of Renispora flavissima.

Aspects of the fine structural characteristics of conidial and hyphal cells of the imperfect Chrysosporium state of the newly reported gymnoascaceous fungus, Renispora flavissima, are described and illustrated by electron micrographs of ultrathin sections. Preservation of the substructure of the thick-walled, smooth to tuberculate conidia was best achieved after fixation in permanganate. The conidial wall consisted of two conspicuous zones (or layers) of varying thickness, texture, and electron opacity. The tuberculate ornamatations arose as extensions of the electron opaque outer zone. The outer layer(s) of the conidial wall proper was continuous with an outer wall layer of the conidiogenous hypha. The conidial cytoplasm was cytologically complex containing numerous but typical fungal inclusions and organelles scattered throughout. This ultrastructural feature of the tuberculate conidia of the Chrysosporium sp. differs from that observed for the morphologically similar large tuberculate conidia of the zoopathogenic Histoplasma capsulatum.

Structure of chitin in the cell walls of newly formed and mature conidia of Fusarium sulphureum

Samples of 7-day-old septate conidia (mature conidia) and newly released aseptate ones (immature conidia) of Fusarium sulphureum were hydrolyzed successively in KOH, acetic acid – H2O2, and H2SO4. The cell wall residue of the mature conidia remained intact throughout the hydrolysis but that of immature conidia dissolved in the H2SO4. Thus, the immature conidial cell wall is substantially different from that of mature conidial cells or growing hyphae and the cell wall undergoes a structural transformation following conidium release from the conidiogenous cell. X-ray diffraction analyses of the wall residues following KOH and acetic acid – H2O2 hydrolysis showed that the mature conidial wall residue had a crystalline chitin component, while the residue of the immature conidial wall was more amorphous and had smaller crystals. An X-ray diffraction pattern of the dissolved immature conidial wall that was recovered from the H2SO4 hydrolysate showed that it contained crystalline chitin.Infrared spectroscopic analysis of the mature conidial cell wall residue showed absorption bands due to inter- and intra-molecular hydrogen bonding and for hydrogen stretching associated with crystalline chitin. Such bands were lacking in the immature cell wall analogue.

Cell constituents of mycelia and conidia of Aspergillus fumigatus

Cell-wall components of mycelia and conidia of Aspergillus fumigatus contain alkali-soluble polysaccharides comprised of d-galacto- d-mannans which coprecipitated with small proportions of a d-glucan, tentatively identified as glycogen. The fine structures of the d-galacto- d-mannans varied as a function of the cell type. In a 5-day-old mycelium, the polysaccharide consisted of a main chain of (1→6)-linked α- d-mannopyranose residues substituted at O-2 by 1 to 3 α- d-mannopyranosyl units that are (1→2)-interlinked. β- d-Galactofuranosyl units are (1→6)-linked to the d-mannan core, being components of side-chains of average length of ∼6 units, which are (1→5)-interlinked. The 10-day-old mycelium had a similar d-galacto- d-mannan, but the proportion of glycogen was smaller. Conidia contain polysaccharides of different structure, as shown by the 13C-n.m.r. spectrum and by methylation analysis. Side chains composed of a single unit of β- d-galactofuranosyl linked (1→6) to adjacent d-mannopyranosyl units were identified with a minor proportion of 6- O-substituted d-galactofuranosyl units. Also present were nonreducing d-galacto-pyranosyl end-groups and 2-amino-2-deoxyglycosyl units. The glucan component was not glycogen. Conidial walls have much less protein than mycelial walls. Predominant amino acids in the latter were aspartic and glutamic acids, tyrosine, alanine, and glycine. Fatty acids C 16, C 18, C 18:1, and C 18:2 were present in the mycelial and conidial walls, C 18:2 was present in minor amounts in the mycelial wall, but was a major component of the lipid fraction from whole cells.

Infundibura, a new hyphomycete with unique appendages

A new hyphomycete is described with gelatinous, sporodochioid conidiomata; holoblastic-solitary conidia with a characteristic basal footlike process, a funnel-shaped, mucoid, apical appendage, and a terete, mucoid basal appendage. The novel mode of appendage development by gelatinization of predetermined areas of conidium wall and significance in conidium secession and dispersal are examined.

Ultrastructure and Chemistry of cell walls of Geotrichum candidum: with special reference to Conidiogenesis.

The conidiogenesis of Geotrichum candidum grown on Czapek agar containing 1% yeast extract was examined by electron microscopy. The results showed that the entire wall of the fertile hypha is incorporated into the conidial wall and also that increase in thickeness of the inner wall layer and differentiation of crosswalls are likely to be due to new wall synthesis which occur during conidium formation. Furthermore, the chemical composition was analysed for the purified conidial walls, and was compared with that of haloarthric conidial walls produced by Trichophyton mentagrophytes.

Conidium germination in the Chalara state of Ceratocystis adiposa: A light and electron microscope study

Germination of the conidia of the Chalara state of Ceratocystis adiposa , at the light and electron microscope level, is described. Germ-tube production is by the polarized growth of a newly deposited inner layer of the conidium wall. This mode of germination is discussed in relation to recent reports on spore germination.

Authors' reply

Botryosphaeria spp. are common endophytes of woody plants, and they also include some serious pathogens of Eucalyptus and Acacia species. Numerous anamorphs have been associated with Botryosphaeria, of which the species Fusicoccum are amongst the most common. Here, we characterize two new Fusicoccum species, isolated from Eucalyptus and Acacia trees in Venezuela, based on morphological features in culture and comparisons of DNA sequence data. The two taxa named Fusicoccum andinum and F. stromaticum spp. nov, reside in two well-supported clades (BS values = 100 %) based on a combined data set of the ITS of the rDNA operon and translation elongation factor 1-α (EF1- α) gene sequences. The conidia of F. andinum are unusually large amongst Botryosphaeria anamorphs, and peripherally resemble those of B. mamane and B. melanops. F. stromaticum is characterized by large conidiomata in cultures, growth at 35 °C and slightly thickened conidial walls, which is different to most other Fusicoccum spp. No teleomorphs were observed for these fungi, but DNA sequence data show that they are anamorphs of Botryosphaeria.

Coelomycetes on Liliales: Dothiorella smilacina and Stagonospora smilacis

The fungi related to Dothiorella smilacina (Peck) Petrak & Sydow and Stagonospora smilacis (Ellis & Everh.) Saccardo were studied. Because of the continuity of variation observed in the available herbarium material and in numerous isolates, a large number of epithets are placed in synonymy with Macrophoma smilacina (Peck) Berl. & Vogl. Two varieties are distinguished for the species, with M. smilacina var. smilacis (Ellis & Everh.) comb. nov. differing from M. smilacina var. smilacina primarily in the production of a pigment in the walls of mature conidia of the former. Both varieties are widely distributed in North America with hosts in Liliaceae (Asparagoideae and Melanthioideae) and Smilacaceae.

Surface ultrastructure and chemical composition of the cell walls of conidial fungi

Freeze-fractures of the conidial wall surface of the deuteromycetous fungi Penicillium sp., Cladobotryum varium, Cladosporium macrocarpum, and Aspergillus niger and of the sporangiospore surface of the zygomycetous fungus Mycotypha microspora reveal rodlet fascicles. Shadow replicas and deep-etching of these cells demonstrate an outermost amorphous layer adjacent to the rodlet fascicles. In each case, individual rodlets are apparently composed of chains of subunits (approx 50 A diam) while interdigitated fascicles consist of clusters of rodlets arranged in parallel. The conidial wall of A. niger was separated into an outer and inner layer by passing the cells through a cell fractionator. Rodlets were present on the extracellular surface of the isolated and purified outer layer, but absent from the inner layer. The hyphal wall of A. niger was also isolated and purified. A comparison of the chemical composition of the three wall layers demonstrated distinct quantitative differences in total carbohydrate, monosaccharide, total hexosamine, peptide, and lipid content. On the basis of the gross chemical composition of the outer conidial wall layer, as well as data obtained from enzymatic digestion and various chemical treatments of this layer followed by ultrastructural examinations, it is suggested that rodlets of A. niger are mainly proteinaceous.

Conidium ultrastructure and wall architecture in the Chalara state of Ceratocystis adiposa

When cultured on different media the Chalara state of Ceratocystis adiposa (Butl.) C. Moreau forms conidia of varying morphology. The major variation is in the thickness, elaboration and pigmentation of the wall of the coniduim. The appearance of conidial walls after chemical and enzymic treatments, and their binding properties with plant lectins is described. A model is proposed to show the distribution of polymers throughout the three wall layers.

Cell wall composition in different cell types of the dimorphic species Sporothrix schenckii

Cell wall components from the yeast, mycelial, and conidial forms of Sporothrix schenckii were compared. Mycelial and conidial walls were qualitatively and quantitatively similar. Minor differences included slightly higher levels of protein and carbohydrate and lower levels of lipids and phosphate in the conidial as compared to the mycelial cell walls. In contrast, yeast walls had higher contents of total carbohydrate, mainly water- and alkali-soluble polysaccharides, and lower contents of proteins and lipids. The lipid fraction from the yeast walls contained a different proportion of saturated and unsaturated fatty acids, including a C18:3 acid which was absent in the acid-extractable lipid fraction from mycelial and conidial walls. The amino acid composition of proteins from the yeast walls also differed from that of the other cell types mainly by containing more threonine, serine, and alanine and less lysine, arginine, and glutamic acid.

Sterol Metabolism during Germination of Conidia of Aspergillus fumigatus

The sterol content of germinating conidia of the opportunistic pathogenic fungus Aspergillus fumigatus has been correlated with germination phase and sensitivity to polyene antibiotics. The sterol and sterol ester contents of walls did not change during germination. The sterol ester content of membranes and cell sap remained constant during germination, whereas the sterol content increased during the outgrowth of germ tubes. On the basis of differential extraction studies it was concluded that the loss of resistance to polyenes that occurred in the early stages of swelling of conidia during germination was not due to a movement of sterol or sterol ester out of the wall. Radioactive-labelling experiments demonstrated that, although the amounts of conidial wall sterol and sterol ester did not change during germination, they were metabolically active. Changes in the turnover rate of wall and membrane sterol and sterol ester during germination were investigated and their relationship to a possible mechanism for the change from resistance to sensitivity to polyene antibiotics is discussed.

Cell wall of Fusarium sulphureum. II. Chemical composition of the conidial and chlamydospore walls.

Examination of the conidial and chlamydospore walls of Fusarium sulphureum by electron microscopy showed the presence of two distinct layers of differing electron densities. These include a relatively narrow outer electron-dense layer and a broader more transparent inner layer. Both chlamydospore cell wall layers were thicker than the conidial wall. The outer wall of the chlamydospore wall was 30% thicker while the inner cell wall layer was 250% thicker than the corresponding cell wall layers in the conidia. During conidial differentiation to form chlamydospores there was a considerable augmentation of all cell wall components which varied from 7 to 26-fold per cell. The augmentation of the major cell wall constituents (N-acetylglucoseamine (NAG), glucose, and protein) and the vast increase in the inner cell wall of the chlamydospore wall indicated that these newly synthesized constituents are predominently located in the inner cell wall layer.The major carbohydrate constituents on a dry weight basis in both the conidial and chlamydospore walls were glucose, glucuronic acid, and N-acetylglycosamine (NAG). However, the proportion of these and the other carbohydrate constituents were different for both spore walls. Thus, the conidial wall contained about 50% less NAG and glucuronic acid but twice the glucose content of the chlamydospore wall. Protein was a major component of both spore walls (21.6%, conidial wall; 28.5%, chlamydospore wall). Amino acid analysis indicated differences in the types of protein present in the two spore walls. The lipid content of both conidia and chlamydospore was low (1–2%).

Dolipore disjunction in Antromycopsis broussonetiae pat

Antromycopsis brousonnetiae , the coremioid imperfect state of Pleurotus cystidiosus , produces numerous phaeospores in a terminal mucous drop. The conidia are arthrospores and cell disarticulation requires cleavage of clamp and hyphal dolipores. Aspects of this sequence have been examined electron microscopically. The outer wall of the developing spore initially has a homogeneous light appearance like that of the hyphae, but as it matures it becomes dark and coarsely fibrous, a change that may result from a gelatinization associated with mucous drop formation. The first apparent indication of new conidial wall material is the appearance of barred material in the dolipore cusp of the future spore. Subsequently the new conidial wall forms beneath the degenerating outer wall. This secondary wall is composed of dark micelles oriented parallel to the cell surface. It is a thick wall and most of its middle is traversed by what appears to be a regular pattern of pores. In the course of spore maturation it seems that the half of the dolipore within the spore breaks down, that the socket becomes filled with conidial wall material, and that the occlusion and parenthesome disappear. The precursor of the wall material may be striated inclusions found in the synnemal apex. This material is believed to be organized as leaflet stacks of dark material that probably arise free in the cytoplasm and then become sequestered in vacuoles.

The fine structure of conidial development in the genus Torula. III. T. graminis Desm.

Torula graminis produced blastoconidia in acropetalous chains after the evagination of a characteristic conidiogenous cell. Conidia consisted of up to 15 cells and their cell wall was differentiated into an outer melanized zone and an inner hyaline zone. A consistent cytoplasmic feature of conidial cells was the presence of dictyosomal-like membranous stacks often closely associated with the nucleus. Vesicles that developed from the dictyosomal-like cisternae were probably involved in conidial wall synthesis.

Lipids from conidia of Erysiphe graminis tritici (powdery mildew)

Lipids of conidia of Erysiphe graminis tritici were analysed by thin-layer chromatography, gas chromatography and mass spectrometry. Saturated and unsaturated hydrocarbons (such as C 17 , C 19 , C 21:1 and C 25:1 and naturally occurring methyl esters of long-chain fatty acids (C 17 to C 25 ) were detected. The free fatty acids ranged from C 12 to C 24 and unsaturated fatty acids such as C 22:1 and C 24:1 were present. The conidial walls had different appearances when processed with scanning electron microscopy, freeze-etching and thin-sectioning procedures. Lipid bodies were not present in lipid extracted conidia and spore walls of lipid extracted conidia characteristically had electron dense tripartite layers and clumped together.

Some chemical and structural features of the conidial wall of Trichoderma viride

Cell wall of spores of Trichoderma viride contains polymers similar to those of mycelial cell wall, such as beta-(1 leads to 3), beta-(1 leads to 6) glucans and protein, but chitin, always present in the mycelium, cannot be found in spores. Melanin, which in other fungi appears associated with chitin, replaces this polymer in the spore wall of T. viride and is located in the outermost layer. Attempts to characterize the pigment of the spore wall indicate that it is a non-indolic melanin-like polyphenol.

An electron microscope study of spore germination in Fusarium sambucinum var. coeruleum

The ultrastructure of resting and germinating Fusarium sambucinum var. coeruleum Wr. conidia was studied with the scanning electron microscope (SEM) and the transmission electron microscope (TEM). Special attention was paid to the effect of osmotic pressure during fixation and washing, which had to be kept constant and fairly low, in order to observe conidial swelling. During germination the mitochondria seemed to become smaller and more numerous and dense bodies became vacuolate. The septal plugs remained in or next to the septal pores. The wall of the germ tube seemed to extend from the inner layer of the conidial wall.

Microcycle conidiation in Penicillium urticae: an ultrastructural investigation of conidiogenesis.

A cultivation system has been developed for Penicillium urticae which yields 'microcycle' conidiation in submerged culture. Spherical growth of spores was initiated by incubation at 37 degrees C in a growth-favoring medium. Transfer of these enlarged spores to a nitrogen-poor medium at 35 degrees C results in synchronous germination and limited outgrowth followed by roughly synchronous conidiation. A study of the conidiation stage showed that a phialide and an immature conidium began to form at the tip of all germ tubes 18 h after the temperature shift. By 24 h additional phialides commonly appeared as a branch near the tip of the germ tube and the more mature conidia exhibited increasing refractility. The earliest ultrastructural signs of conidiation were various round invaginations in the plasma membrane and a thickening and rounding of the new spore wall which appeared as an inner extension of the phialide cell wall. Upon segregation of the conidium from the phialide cell by conidial wall formation, 'trench-like' invaginations gradually appeared in the plasma membrane and a disorganized rodlet pattern was formed on the outer surface of the maturing conidial wall. Continued maturation involved the formation of chains of conidia and phialide senescence which was characterized by a general degradation of intracellular structure. A comparison with standard surface and submerged culture conidiation indicated that 'microcycle' conidiation, while less prolific, was essentially identical.