Involvement of actin filaments in rhizoid morphogenesis of Spirogyra

The role of actin filaments in rhizoid morphogenesis was studied in Spirogyra . When the algal filaments were severed, new terminal cells started tip growth and finally formed rhizoids. Actin inhibitors, latrunculin B and cytochalasin D, reversibly inhibited the process. A mesh-like structure of actin filaments (AFs) was formed at the tip region. Gd³⁺ inhibited tip growth and decreased AFs in the tip region. Either a decrease in turgor pressure or lowering of the external Ca²⁺ concentration also induced similar results. It was suggested that the mesh-like AF structure is indispensable for the elongation of rhizoids. A possible organization mechanism of the mesh-like AF structure was discussed.     

Ste20-related kinases: effectors of signaling and morphogenesis in fungi

The family of Ste20-related kinases is conserved from yeast to mammals and includes the p21 activated kinases (PAKs) and germinal centre kinases (GCKs). These kinases have been shown to be involved in signaling through mitogen activated protein kinase (MAPK) pathways and in morphogenesis through the regulation of cytokinesis and actin-dependent polarized growth. This review concentrates on the role of Ste20-related kinases in fungi where recent research has revealed roles for both PAKs and GCKs in the regulation of cytokinesis and in previously unidentified roles in promoting hyphal growth and differentiation of asexual development structures. In particular, the importance of PAKs during pathogenesis will be examined.     

Chitinases of fungi and plants: their involvement in morphogenesis and host-parasite interaction

Abstract: There has been a considerable amount of recent research aimed at elucidating the roles of chitinase in fungi and plants. In filamentous fungi and yeasts, chitinase is involved integrally in cell wall morphogenesis. Chitinase is also involved in the early events of host-parasite interactions of biotrophic and necrotrophic mycoparasites, entomopathogenic fungi and vesicular arbuscular mycorrhizal fungi. In plants, induction of chitinase and other hydrolytic enzymes is one of a coordinated, often complex and multifaceted defense mechanism triggered in response to phytopathogen attack. Chitinase induction in plants is not considered solely as an antifungal resistance mechanism. Plant chitinases can be induced by various abiotic factors as well and there is some circumstantial evidence to suggest a morphogenetic role despite the apparent absence of the substrate in plant cells. Finally, some chitinases and other chitin-binding proteins including some plant lectins share chitin-binding domains as part of their molecular structure and provide fuel for the so-called 'lectin-chitinase' debate and speculation for the origin of chitinase in plants.     

Copper resistance mechanisms in bacteria and fungi

Abstract: Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chromosomal and plasmid copper-resistance systems in bacteria have been reported, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced effiux of cupric ions, or copper complexation by cell components. Copper tolerance in fungi has also been ascribed to diverse mechanisms involving trapping of the metal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothionein chelation mechanism has been approached with molecular detail.     

Studies on the physiological bases of morphogenesis in fungi; the respiratory metabolism of dimorphic pathogenic fungi

The interconversions of mycelial and yeast-like forms (M right harpoon over left harpoon Y) in Blastomyces dermatitidis and in Blastomyces brasiliensis are characterized as examples of thermal dimorphism since the phenomena are apparently dependent only on the temperature of incubation of these two species. The change in morphology consequent upon Y --> M conversion is considered to result from the selective inhibition of cell division, without the simultaneous inhibition of growth. Such selective inhibition is viewed in a wider context as an example of the differential operation of the physicochemical apparatus of the cell in the control of form development by an organism. To analyze this differential operation, which is here dependent only on temperature, we have studied the effect of temperature on oxygen consumption by each of the dimorphic forms. In the absence of external substrate the yeast forms consume 5 to 6 times more oxygen per unit dry weight than do the M forms.The Y forms exhibit an exogenous oxidation of acetate and of glucose, as well as an oxidative assimilation of these substrates, whereas the M forms exhibit no exogenous metabolism in either a resting or starved condition. A study of the effect of a wide range of temperatures on oxygen consumption by the M forms indicates the operation of two rate-limiting processes: (a) one with an activation energy of 13,250 calories/gm. molecule over the range 5-30 degrees , and (b) reversible enzyme inactivation; the latter process assuming importance in the higher temperature range. On abrupt, large changes in temperature the balance between these two rate-limiting reactions (which it is suggested characterizes the steady state) is apparently disrupted as a result of a lag in the assumption of a rate of reversible enzyme inactivation characteristic of the new temperature. This disruption of balance is evidenced in overshoot phenomena. The effect of an analogous disruption of balance, and of increasing enzymic inactivation; on a competition between enzyme systems, competing for substrate for cell elongation and for cell division, is considered in explanation of the observed dependence of the cell division mechanism on the maintenance of an elevated temperature.     

Interactions among endophytic bacteria and fungi: Effects and potentials

Plants benefit extensively by harbouring endophytic microbes. They promote plant growth and confer enhanced resistance to various pathogens. However, the way the interactions among endophytes influence the plant productivity has not been explained. Present study experimentally showed that endophytes isolated from rice (Oryza sativa) used as the test plant produced two types of interactions; biofilms (bacteria attached to mycelia) and mixed cultures with no such attachments. Acidity, as measured by pH in cultures with biofilms was higher than that of fungi alone, bacteria alone or the mixed cultures. Production of indoleacetic acid like substances (IAAS) of biofilms was higher than that of mixed cultures, fungi or bacteria. Bacteria and fungi produced higher quantities of IAAS than mixed cultures. In mixed cultures, the potential of IAAS production of resident microbes was reduced considerably. There was a negative relationship between IAAS and pH of the biofilms, indicating that IAAS was the main contributor to the acidity. However, such a relationship was not observed in mixed cultures. Microbial acid production is important for suppressing plant pathogens. Thus the biofilm formation in endophytic environment seems to be very important for healthy and improved plant growth. However, it is unlikely that an interaction among endophytes takes place naturally in the endophytic environment, due to physical barriers of plant tissues. Further, critical cell density dependant quorum sensing that leads to biofilm formation may not occur in the endophytic environment as there is a limited space. As suchin vitro production and application of beneficial biofilmed inocula of endophytes are important for improved plant production in any agro-ecosystem. The conventional practice of plant inoculation with monocultures or mixed cultures of effective microbes may not give the highest microbial effect, which may only be achieved by biofilm formation.     

Orchestration of morphogenesis in filamentous fungi: conserved roles for Ras signaling networks

Filamentous fungi undergo complex developmental programs including conidial germination, polarized morphogenesis, and differentiation of sexual and asexual structures. For many fungi, the coordinated completion of development is required for pathogenicity, as specialized morphological structures must be produced by the invading fungus. Ras proteins are highly conserved GTPase signal transducers and function as major regulators of growth and development in eukaryotes. Filamentous fungi typically express two Ras homologs, comprising distinct groups of Ras1-like and Ras2-like proteins based on sequence homology. Recent evidence suggests shared roles for both Ras1 and Ras2 homologs, but also supports the existence of unique functions in the areas of stress response and virulence. This review focuses on the roles played by both Ras protein groups during growth, development, and pathogenicity of a diverse array of filamentous fungi.     

Growth of fungi and bacteria in the reciprocating jet bioreactor

In a comprehensive study the properties of the reciprocating-jet-bioreactor have been investigated. Fermentations have been carried out with two fungi and one bacterium. The fungi were Cyathus striatus for the production of antibiotics and Aspergillus niger for the production of citric acid. The bacterium Zymomonas mobilis was used in an anaerobic fermentation for the production of ethanol. The reciprocating-jet-bioreactor showed excellent properties as fermenter, especially when the biosuspension is highly viscous and non-Newtonian by nature.Lecture held on the occasion of the Third Joint Schlesinger Seminar at the Institute of Technology of the Technion-Haifa, May, 8–9th, 1990     

Growth of saprotrophic fungi and bacteria in soil

Bacterial and fungal growth rate measurements are sensitive variables to detect changes in environmental conditions. However, while considerable progress has been made in methods to assess the species composition and biomass of fungi and bacteria, information about growth rates remains surprisingly rudimentary. We review the recent history of approaches to assess bacterial and fungal growth rates, leading up to current methods, especially focusing on leucine/thymidine incorporation to estimate bacterial growth and acetate incorporation into ergosterol to estimate fungal growth. We present the underlying assumptions for these methods, compare estimates of turnover times for fungi and bacteria based on them, and discuss issues, including for example elusive conversion factors. We review what the application of fungal and bacterial growth rate methods has revealed regarding the influence of the environmental factors of temperature, moisture (including drying/rewetting), pH, as well as the influence of substrate additions, the presence of plants and toxins. We highlight experiments exploring the competitive and facilitative interaction between bacteria and fungi enabled using growth rate methods. Finally, we predict that growth methods will be an important complement to molecular approaches to elucidate fungal and bacterial ecology, and we identify methodological concerns and how they should be addressed.     

Thermophilic fungi in the mycoflora of man and environmental air

The objective of this study was to determine if thermophilic fungi exist in the mycoflora of man and in the aeroflora of his environment.Humicola lanuginosa andHumicola grisea were isolated from 5 of 55 samples of outside air. Three thousand cultures were taken from the nasal mucosae, skin surfaces and recta of 570 children. Cultures were incubated at 50°C. Thermophilic fungi were isolated from 6 of 287 children receiving immunosuppressive therapy for malignancies and from 1 of 283 normal children.H. lanuginosa was recovered from the skin of one, the rectum of one and the nasal mucosae of three patients.Mucor pusillus was isolated from the nasopharynges of two patients.Further studies are now indicated to determine the pathogenicity of these organisms with respect to tissue invasive disease, antigenicity and metabolite toxicity.Supported by General Research Support Grant RR-05584 from National Institutes of Health; Cancer Research Center Grant CA-08480 and Training Grant CA-05176 from the National Cancer Institute, National Institutes of Health and by ALSAC.     

生防真菌分生孢子抗氧化能力与多糖含量的关系

作为重要的丝孢类昆虫病原真菌,球孢白僵菌和玫烟色棒束孢因其易于生产和环境友好等优点而在害虫生防防治中受到广泛青睐。为初步探求孢子耐氧化力及其与孢子多糖含量的关系,球孢白僵菌和玫烟色棒束孢11株菌经胁迫后的残存指数随氧化剂H2O2浓度增加而减小。所有菌株的残存指数均能良好地与Logistic方程拟合,并计算出各菌株在氧化胁迫条件下的半致死浓度。结果显示玫烟色棒束孢孢子的耐氧化力强于球孢白僵菌。两种真菌的分生孢子耐氧力与各自多糖含量呈现良好线性正相关。培养基碳源成分和浓度变化可影响球孢白僵菌孢子耐氧化力,但耐氧化力与多糖含量依旧呈现线性正相关。由此可见,生防真菌分生孢子的耐氧化力的确与多糖积累有关,并在一定程度上受培养条件的调节。研究结果有望为提高生防真菌孢子环境稳定性提供新的策略。