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PubMed2006

Developmental control of a parAB promoter leads to formation of sporulation-associated ParB complexes in Streptomyces coelicolor.

The Streptomyces coelicolor partitioning protein ParB binds to numerous parS sites in the oriC-proximal part of the linear chromosome. ParB binding results in the formation of large complexes, which behave differentially during the complex life cycle (D. Jakimowicz, B. Gust, J. Zakrzewska-Czerwinska, and K. F. Chater, J. Bacteriol. 187:3572-3580, 2005). Here we have analyzed the transcriptional regulation that underpins this developmentally specific behavior. Analysis of promoter mutations showed that the irregularly spaced complexes present in vegetative hyphae are dependent on the constitutive parABp(1) promoter, while sporulation-specific induction of the promoter parABp(2) is required for the assembly of arrays of ParB complexes in aerial hyphae and thus is necessary for efficient chromosome segregation. Expression from parABp(2) depended absolutely on two sporulation regulatory genes, whiA and whiB, and partially on two others, whiH and whiI, all four of which are needed for sporulation septation. Because of this pattern of dependence, we investigated the transcription of these four whi genes in whiA and whiB mutants, revealing significant regulatory interplay between whiA and whiB. A strain in which sporulation septation (but not vegetative septation) was blocked by mutation of a sporulation-specific promoter of ftsZ showed close to wild-type induction of parABp(2) and formed fairly regular ParB-enhanced green fluorescent protein foci in aerial hyphae, ruling out strong morphological coupling or checkpoint regulation between septation and DNA partitioning during sporulation. A model for developmental regulation of parABp(2) expression is presented.

Bacterial Proteins↗
PubMed1963

NUCLEOTIDE COMPOSITION OF RIBONUCLEIC ACID FROM NEUROSPORA CRASSA.

Henney, H. (The University of Texas, Austin) and R. Storck. Nucleotide composition of ribonucleic acid from Neurospora crassa. J. Bacteriol. 85:822-826. 1963.-The nucleotide composition of total, ribosomal, and soluble ribonucleic acid (RNA) from the conidia and the hyphae of Neurospora crassa was determined. The corresponding RNA classes from the two morphological types had the same base ratio. Total, ribosomal, and soluble RNA from hyphae contained, respectively, 51.0, 50.2, and 61.6% guanylic acid (G) plus cytidylic acid (C), and from conidia, 50.6, 49.9, and 62.1%. The proportion of nucleotides in ribosomal RNA was in close agreement with that reported for ribosomal RNA from other organisms. Soluble RNA contained 2.8% pseudouridylic acid, 36.0% C, and 25.5% G, and differed from soluble RNA from other sources in its high C content. Centrifugation of purified RNA from conidia and hyphae, through a linear sucrose-density gradient, yielded identical sedimentation profiles.

Neurospora↗
PubMed1963

EFFECTS OF THE ANTIFUNGAL PEPTIDE RO 2-7758 ON MORPHOLOGY OF MUCOR CORYMBIFERA.

Gale, Glen R. (Veterans Administration Hospital and Duke University Medical Center, Durham, N.C.). Effects of the antifungal peptide Ro 2-7758 on morphology of Mucor corymbifera. J. Bacteriol. 85:833-837. 1963.-Hyphae of Mucor corymbifera grown in the presence of the antifungal peptide, Ro 2-7758, were examined in an electron microscope. The predominant change, compared with control hyphae, was a marked thickening of the cell wall, with apparent maintenance of normal structure. Cell walls of control hyphae were from 0.03 to 0.11 mu in thickness; drug-treated walls varied from 0.22 to over 0.75 mu in thickness. The possible sites and mechanisms of action, as well as the significance of a thickened cell wall in antibiosis, are discussed.

Antifungal Agents↗
PubMed1965

ELECTRON MICROSCOPIC OBSERVATION OF THE SPORANGIAL STRUCTURE OF A STRAIN OF ACTINOPLANES.

Lechevalier, Hubert (Rutgers, The State University, New Brunswick, N.J.), and Pauline E. Holbert. Electron microscopic observation of the sporangial structure of a strain of Actinoplanes. J. Bacteriol. 89:217-222. 1965.-Actinoplanes sp. P 128 has polarly flagellated sporangiospores. The numerous flagella, formed by the helical winding of subfibrils, were seen clearly only in shadowed preparations. Flagella were never seen in sections of spores. Sporangial formation was followed by examining sections of sporangia at various stages of maturity. The sporangial envelope was the continuation of the outer sheath of the sporangiophore. The sporangiospores were formed by the division of hyphae enclosed within the sporangial wall. The spores were probably formed by simultaneous division of these hyphae. An intersporal substance, which seemed to originate from the outer sheaths of the intrasporangial hyphae, could be seen.

Actinomycetales↗
PubMed1966

Susceptibility and resistance of several fungi to microbial lysis.

Potgieter, H. J. (Cornell University, Ithaca, N.Y.), and M. Alexander. Susceptibility and resistance of several fungi to microbial lysis. J. Bacteriol. 91:1526-1532. 1966.-Strains of Streptomyces, Nocardia, and Pseudomonas capable of lysing hyphae of Fusarium solani or Neurospora crassa were obtained by selective culture, but attempts to isolate an organism lysing Rhizoctonia solani failed. When provided with F. solani or N. crassa as carbon sources, the actinomycetes tested produced beta-(1 --> 3) glucanase and chitinase. A mixture containing purified chitinase and beta-(1 --> 3) glucanase induced spheroplast formation in F. solani, caused some morphological changes in N. crassa, but had almost no effect on R. solani hyphae. The polysaccharides in R. solani walls, which contain a large amount of glucose as well as galactose, mannose, and glucosamine, were not hydrolyzed appreciably by the two enzymes. Laminaribiose and laminaritriose were released by enzymatic hydrolysis of F. solani and N. crassa walls, and gentiobiose was liberated from R. solani and N. crassa walls. Melaninlike materials were found in R. solani walls, accounting for 8.50% of the wall weight. A role for melanin in protecting hyphae from microbial lysis is suggested.

Basidiomycota↗
PubMed1966

Electron microscopic observation of the sporangial structure of strains of Actinoplanaceae.

Lechevalier, Hubert A. (Rutgers, The State University, New Brunswick, N.J.), Mary P. Lechevalier, and Pauline E. Holbert. Electron microscopic observation of the sporangial structure of strains of Actinoplanaceae. J. Bacteriol. 92:1228-1235. 1966.-Eight strains of Streptosporangium spp. and one strain each of Spirillospora albida and an Ampullariella-like Actinoplanes sp. were observed by electron microscopy. The sporangiospores of all these organisms had a smooth surface. All formed their sporangia by the ingrowth of a hypha inside a bag formed by the extension of the outer sheath of the sporangiophore. The sporogenic hypha was not branched in strains of Streptosporangium but was branched in S. albida and the Actinoplanes sp. Spore formation was by septation of the intrasporangial hyphae. When it occurred, septation took place by the same annular ingrowth of the cell wall common in gram-positive bacteria. The septum at the apex of the sporangiophore was formed before the others. Septation was seen to occur between two fully formed septa, indicating almost simultaneous formation of large segments dividing again, almost simultaneously, into smaller spore-sized segments.

Actinomycetales↗
PubMed1968

Mycelial phase of Paracoccidioides brasiliensis and Blastomyces dermatitidis: an electron microscope study.

A comparative study of the mycelial phase of Paracoccidioides brasiliensis and Blastomyces dermatitidis reveals that both fungi are very much alike, containing multiple nuclei and nuclear pores, mitochondria, ribosomes, scarce endoplasmic reticulum, intracytoplasmic membrane systems, glycogen, and vacuoles. Shadowed cell walls show fine fibrillar surfaces that contrast with those in the yeast phase. The intracytoplasmic membrane system is continuous with the plasma membrane and is similar to bacterial mesosomes. Granules with light cores and dark rims are observed in the plasma membrane. Live hyphae growing inside a dead hypha are found much more frequently in immersed cultures than in solid-medium cultures, suggesting that breakage of the hypha could elicit this phenomenon.

Blastomyces↗
PubMed1985

Pure spherules of Coccidioides immitis in continuous culture.

Investigation of host-parasite relationships involving the parasitic form of Coccidioides immitis has been difficult because, previously, spherules and endospores have not been grown continuously in tissue culture medium without detectable formation of hyphae. Arthroconidia were harvested from mycelial cultures and inoculated into tissue culture flasks which contained RPMI 1640 medium supplemented with 10% calf serum and N-Tamol (Rohm & Haas Co., Philadelphia, Pa.). Flasks were purged with 5% CO2, sealed, and placed on a reciprocating shaker at 35 degrees C. Hyphae which arose during incubation were removed by filtration. Arthroconidia readily converted to the spherule-endospore form within 12 days. Six days after complete conversion, spherules and endospores were transferred to RPMI 1640 without N-Tamol. The spherule-endospore cycle was maintained in tissue culture medium for 84 days without the formation of detectable hyphae.

Coccidioides↗
PubMed1986

Osteolytic phaeohyphomycosis in a German shepherd dog caused by Phialemonium obovatum.

Phialemonium obovatum was found to be the cause of osteomyelitis in a German shepherd dog. Histologic examination of the biopsied material from the left tibia revealed septate, irregularly branched hyphae, swollen cells, and ovate-to-spherical cells divided by a transverse septum. The majority of the fungal elements were hyaline, but a few had lightly pigmented cell walls that had a greenish yellow tint. The presence of melanin in the cell walls of the hyphae and especially in their septa was verified by the use of the Fontana-Masson silver stain. P. obovatum formed moist, off-white-to-ochraceous, spreading colonies with a characteristic green pigment on their reverse side. The pigment was more prominent in cultures grown at 37 degrees C than in those grown at 25 degrees C. The isolate also grew at 40 degrees C. The dog isolate produced characteristic adelophialides without conspicuous collarettes and also basal septa from the creeping vegetative hyphae growing on the surface of the medium. The numerous obovate phialoconidia were smooth and one-celled.

Animals↗
PubMed1994

Developmental decisions in Aspergillus nidulans are modulated by Ras activity.

To better understand how Ras controls development of multicellular organisms, we have chosen Aspergillus nidulans as a model system. When grown on solid medium, this fungus follows a well-defined program of development, sequentially giving rise to several cell types which produce three distinct structures: vegetative hyphae, aerial hyphae, and the conidiophore structure. Here we describe a ras homolog found in this fungus (Aras) and demonstrate that it is an essential gene that regulates the ordered program of development. We created dominant alleles of this gene and expressed them to different levels in order to vary the ratio of GTP-bound (active) to GDP-bound (inactive) A-Ras protein. When the amount of active Ras is large, nuclear division proceeds, but further development is inhibited at the early step of germ tube formation. At an intermediate level of active Ras, aerial hypha formation is inhibited, while at a low level, conidiophore formation is inhibited. Maintenance of an even lower level of the active Ras is essential for initiation and progression of conidiophore formation, the final stage of development. When the level of active Ras is artificially lowered, each stage of development is initiated prematurely except germination, the initial stage of development. Therefore, the progression of the ordered developmental pathway of A. nidulans is dependent upon an initial high level of active Ras followed by its gradual decrease. We propose that several concentration threshold exist, each of which allows development to proceed to a certain point, producing the proper cell type while inhibiting further development.

Amino Acid Sequence↗
PubMed2000

Regulation of conidiation and adenylyl cyclase levels by the Galpha protein GNA-3 in Neurospora crassa.

We have identified a new gene encoding the G protein alpha subunit, gna-3, from the filamentous fungus Neurospora crassa. The predicted amino acid sequence of GNA-3 is most similar to the Galpha proteins MOD-D, MAGA, and CPG-2 from the saprophytic fungus Podospora anserina and the pathogenic fungi Magnaporthe grisea and Cryphonectria parasitica, respectively. Deletion of gna-3 leads to shorter aerial hyphae and premature, dense conidiation during growth on solid medium or in standing liquid cultures and to inappropriate conidiation in submerged culture. The conidiation and aerial hypha defects of the Deltagna-3 strain are similar to those of a previously characterized adenylyl cyclase mutant, cr-1. Supplementation with cyclic AMP (cAMP) restores wild-type morphology to Deltagna-3 strains in standing liquid cultures. Solid medium augmented with exogenous cAMP suppresses the premature conidiation defect, but aerial hypha formation is still reduced. Submerged-culture conidiation is refractory to cAMP but is suppressed by peptone. In addition, Deltagna-3 submerged cultures express the glucose-repressible gene, qa-2, to levels greatly exceeding those observed in the wild type under carbon-starved conditions. Deltagna-3 strains exhibit reduced fertility in homozygous crosses during the sexual cycle; exogenous cAMP has no effect on this phenotype. Intracellular steady-state cAMP levels of Deltagna-3 strains are decreased 90% relative to the wild type under a variety of growth conditions. Reduced intracellular cAMP levels in the Deltagna-3 strain correlate with lower adenylyl cyclase activity and protein levels. These results demonstrate that GNA-3 modulates conidiation and adenylyl cyclase levels in N. crassa.

Adenylyl Cyclases↗
PubMed2000

Crk1, a novel Cdc2-related protein kinase, is required for hyphal development and virulence in Candida albicans.

Both mitogen-activated protein kinases and cyclin-dependent kinases play a role in hyphal development in Candida albicans. Using an oligonucleotide probe-based screen, we have isolated a new member of the Cdc2 kinase subfamily, designated Crk1 (Cdc2-related kinase). The protein sequence of Crk1 is most similar to those of Saccharomyces cerevisiae Sgv1 and human Pkl1/Cdk9. In S. cerevisiae, CRK1 suppresses some, but not all, of the defects associated with an sgv1 mutant. Deleting both copies of CRK1 in C. albicans slows growth slightly but leads to a profound defect in hyphal development under all conditions examined. crk1/crk1 mutants are impaired in the induction of hypha-specific genes and are avirulent in mice. Consistent with this, ectopic expression of the Crk1 kinase domain (CRK1N) promotes filamentous or invasive growth in S. cerevisiae and hyphal development in C. albicans. The activity of Crk1 in S. cerevisiae requires Flo8 but is independent of Ste12 and Phd1. Similarly, Crk1 promotes filamentation through a route independent of Cph1 and Efg1 in C. albicans. RAS1(V13) can also activate filamentation in a cph1/cph1 efg1/efg1 double mutant. Interestingly, CRK1N produces florid hyphae in ras1/ras1 strains, while RAS1(V13) generates feeble hyphae in crk1/crk1 strains.

Amino Acid Sequence↗
PubMed2001

The basic helix-loop-helix transcription factor Cph2 regulates hyphal development in Candida albicans partly via TEC1.

Candida albicans undergoes a morphogenetic switch from budding yeast to hyphal growth form in response to a variety of stimuli and growth conditions. Multiple signaling pathways, including a Cph1-mediated mitogen-activated protein kinase pathway and an Efg1-mediated cyclic AMP/protein kinase A pathway, regulate the transition. Here we report the identification of a basic helix-loop-helix transcription factor of the Myc subfamily (Cph2) by its ability to promote pseudohyphal growth in Saccharomyces cerevisiae. Like sterol response element binding protein 1, Cph2 has a Tyr instead of a conserved Arg in the basic DNA binding region. Cph2 regulates hyphal development in C. albicans, as cph2/cph2 mutant strains show medium-specific impairment in hyphal development and in the induction of hypha-specific genes. However, many hypha-specific genes do not have potential Cph2 binding sites in their upstream regions. Interestingly, upstream sequences of all known hypha-specific genes are found to contain potential binding sites for Tec1, a regulator of hyphal development. Northern analysis shows that TEC1 transcription is highest in the medium in which cph2/cph2 displays a defect in hyphal development, and Cph2 is necessary for this transcriptional induction of TEC1. In vitro gel mobility shift experiments show that Cph2 directly binds to the two sterol regulatory element 1-like elements upstream of TEC1. Furthermore, the ectopic expression of TEC1 suppresses the defect of cph2/cph2 in hyphal development. Therefore, the function of Cph2 in hyphal transcription is mediated, in part, through Tec1. We further show that this function of Cph2 is independent of the Cph1- and Efg1-mediated pathways.

Amino Acid Sequence↗
PubMed1985

Protein changes during the asexual cycle of Neurospora crassa.

A method for synchronizing conidiation and isolating large numbers of cells at discrete stages of conidia development is described. Using two-dimensional gel electrophoresis, we analyzed the protein profiles of mycelia, aerial hyphae, and conidia and observed that the concentration of 14 polypeptides increase and 38 decrease during the asexual cycle. Twelve polypeptides were present in extracts of aerial hyphae or conidia, but not mycelia, suggesting that they may be conidiation specific. The protein profiles of mutants defective in conidiation were also analyzed. Differences were detected in the two-dimensional profiles of protein extracts from fluffy and wild-type aerial hyphae. Polyadenylated RNA isolated from wild-type mycelia and conidiating cultures was translated in vitro in a rabbit reticulocyte lysate. Differences were detected in the polypeptide products specified by the two RNA populations, suggesting that changes in steady-state levels of polyadenylated RNAs also occur during conidiation.

Cell Differentiation↗
PubMed1991

Mucor dimorphism.

Mucor dimorphism has interested microbiologists since the time of Pasteur. When deprived of oxygen, these fungi grow as spherical, multipolar budding yeasts. In the presence of oxygen, they propagate as branching coenocytic hyphae. The ease with which these morphologies can be manipulated in the laboratory, the diverse array of morphopoietic agents available, and the alternative developmental fates that can be elicited from a single cell type (the sporangiospore) make Mucor spp. a highly propitious system in which to study eukaryotic cellular morphogenesis. The composition and organization of the cell wall differ greatly in Mucor yeasts and hyphae. The deposition of new wall polymers is isodiametric in yeasts and apically polarized in hyphae. Current research has focused on the identity and control of enzymes participating in wall synthesis. An understanding of how the chitosome interacts with appropriate effectors, specific enzymes, and the plasma membrane to assemble chitin-chitosan microfibrils and to deposit them at the proper sites on the cell exterior will be critical to elucidating dimorphism. Several biochemical and physiological parameters have been reported to fluctuate in a manner that correlates with Mucor morphogenesis. The literature describing these has been reviewed critically with the intent of distinguishing between causal and casual connections. The advancement of molecular genetics has afforded powerful new tools that researchers have begun to exploit in the study of Mucor dimorphism. Several genes, some encoding products known to correlate with development in Mucor spp. or other fungi, have been cloned, sequenced, and examined for transcriptional activity during morphogenesis. Most have appeared in multiple copies displaying independent transcriptional control. Selective translation of stored mRNA molecules occurs during sporangiospore germination. Many other correlates of Mucor morphogenesis, presently described but not yet explained, should prove amenable to analysis by the emerging molecular technology.

Carbon↗
PubMed1975

Electron microscopy of vesicular-arbuscular mycorrhizae of yellow poplar. III Host-endophyte interactions during arbuscular development.

Scanning- and transmission-electron microscopy were used to examine developing and mature functional arbuscules in mycorrhizal roots of yellow poplar. Arbuscules developed from intracellular hyphae which branched repeatedly upon penetration into the host cells. Intermediate and late stages of developemnt were characterized by the production of numerous, short, bifurcate hyphae throughout the arbuscule. Mature arbuscules exhibited a coralloid morphology which resulted in a considerable increase in the surface area of the endophyte exposed within the host cells. Distinctive ultrastructural features of arbuscular hyphae included osmiophilic walls, nuclei, abundant cytoplasm, glycogen, and numerous small vacuoles. All arbuscular components were enclosed by host wall material and cytoplasm during development and at maturity. In infected cells, host nuclei were enlarged and the cytoplasm associated with the arbuscular branches typically contained abundant mitochondria, endoplasmic reticulum, and proplastids. Ultrastructural observations suggested that nutrient transfer may be predominantly directed toward the fungal endophyte during arbuscular development and while mature arbuscules remain functional.

Cell Wall↗
PubMed1976

Electron microscopy of vesicular-arbuscular mycorrhizae of yellow poplar. IV. Host-endophyte interactions during arbuscular deterioration 1,2.

Scanning electron stereoscopy and transmission electron microscopy were used to correlate morphological alterations and cytological phenomena associated with deterioration of arbuscules in yellow poplar mycorrhizae. Arbuscular degradation was initiated at the tips of the finest branches and progressed basipetally. Cytoplasm in arbuscular hyphae progressively deteriorated and was followed by collapse of the fungal walls. Degraded portions of the arbuscules aggregated into clumps comprised of host wall material and the distorted fungal walls. Host nuclei, abundant mitochondria, and proplastids were closely associated with arbuscular branches undergoing cytoplasmic deterioration and with clumped portions of the arbuscule which contained degraded hyphal branches. Most of the arbuscules observed had deteriorated to the clumped stage. Some cortical cells contained several clumped arbuscules and nearly mature, intact arbuscules which indicated that reinfection occurs even as degradative phenomena are in progress. It is suggested that substantial quantities of mineral nutrients may be made available to the host via degradation of fungal cytoplasm in the arbuscular hyphae preceding aggregation of degraded hyphae into discrete clumps.

Cell Nucleus↗
PubMed1977

Hyphal interference by Trametes hispida.

The antagonistic activity of Trametes hispida Bagl. in dual culture with Hirschioporus species and other non-basidiomycetous fungi is interpreted as hyphal interference. Hyphae of T. hispida grow into and over colonies of sensitive fungi. Contact with hyphae of T. hispida results in cessation of growth and rapid necrosis of affected cells. Ultrastructural studies of the affected hyphae of Hirschioporus pargamenus (Fr.) Bond. & Sing. showed an early formation of extraplasmalemmal wall deposits, disruption of membrane systems, coagulation of cytoplasm, localized dissolution of walls, and loss of cell contents without penetration by the antagonist.

Basidiomycota↗