Biology and life cycle ofAtelocauda koae,an unusual demicyclic rust

Atelocauda koae, a rust of the native HawaiianAcacia koa, is considered as a demicyclic species, having spermogonial, aecial, and telial states, but is unusual in production of aeciospores simultaneously with teliospores rather than consecutively. Host inoculation with spores of each state separately confirmed that the life cycle was perpetuated by the telial state, but the aeciospores, while capable of germination and stomal penetration, did not produce detectable infection. This rust therefore behaves as a microcyclic species, and appears to be in evolutionary transition toward this reduced state. Teliospores produced vestigial, permanently attached basidiosopores which germinated to produce infective hyphae. The hyphae entered the host either through stomata or penetrated the epidermis directly, with the latter method being more common. Unusual nuclear associated with teliospore germination, in which meiosis occurs in more than one diploid nucleus was observed, in confirmation of an earlier study.     

New and interesting species ofEmericella from Chinese soil

Emericella miyajii, a new species isolated from Chinese soil, is described and illustrated. It is characterized by pale orange to brownish orange colonies on malt extract agar, subglobose to broadly elliptical ascospores with defective four equatorial crests and smooth convex walls, and with anAspergillus anamorph.Emericella undulata is also described as an uncommon species from Chinese soil.     

Relationships among microarthropods,fungi, and their environment

Temporal and spatial relationships in a maple-forest soil among mycophagous microarthropods, total hyphal length, vesicular-arbuscular mycorrhizal (VAM) fungus spores, microfungus diversity, root biomass and some abiotic variables (temperature, water content, pH, organic matter content) were investigated. Samples were obtained from spring 1991 to winter 1992 at four soil depths. Canonical correspondence analysis was used to analyze the data. Four species of sporulating VAM fungi were identified, along with 23 species of mites and springtails, 9 of which were common. Hyphal length, VAM fungus spores, and soil animals peaked in spring and autumn. Canonical correspondence analysis suggests that animal abundance and success in the soil is dependent on a number of environmental variables. The most important variables that influence microarthropod community structure are: (i) temperature, (ii) water content, (iii) pH, (iv) total length of fungal hyphae, and (v) diversity of darkly-pigmented fungi. However, the relative importance of these variables changes with increasing soil depth. We have also shown a relationship between arthropod populations and their food supply under field conditions, a phenomenon that has been demonstrated previously under controlled laboratory conditions.     

Entomopathogenic fungi associated with Ixodes ricinus ticks

The objective of this study was to demonstrate the occurrence of entomopathogenic fungi on Ixodes ricinus ticks in relation to the tick stage, engorgement and season. Ticks were collected from the vegetation, from small rodents and from deer. All entomopathogenic fungi found belonged to the Hyphomycetes. Paecilomyces farinosus and Verticillium lecanii were the predominant species. Other species, found only on engorged females were: Beauveria bassiana, B. brongniartii, P. fumosoroseus and V. aranearum. Eight out of 1833 ticks collected from the vegetation and three out of 269 engorged nymphs were infected with fungi. Thirty-three out of 149 engorged females were infected, whereas males and engorged larvae were not infected. Throughout the season, a significantly higher proportion of ticks collected in autumn were infected. Entomopathogenic fungi may have a significant impact on the size of the I. ricinus population, since females were the most frequently infected stage.     

Gene pho-2 codes for the multiple active forms of Pi-repressible alkaline phosphatase in the mould Neurospora crassa

The mycelial Pi-repressible alkaline phosphatase of the wild-type strain 74A of Neurospora crassa was separated into at least ten isoforms by isoelectric focusing. The components visualized by activity with sodium -naphthyl phosphate as the substrate were predominantly acidic proteins with isoelectric points ranging from pH 4.5 to 7.6. The number of these isoforms was a function of growth pH. Strain pho-2A did not produce active Pi-repressible alkaline phosphatase (the pho-2 gene codes for its amino acid sequence), which gives an indication that these isoforms are encoded by the same structural gene.     

Cloned DNA probes distinguish endemic and exotic Entomophaga grylli fungal pathotype infections in grasshopper life stages

Entomophaga grylli is a fungal pathogen of grasshoppers and at least three pathotypes are recognized world-wide. Pathotypes 1 and 2 are endemic to North America while the Australian pathotype 3 had been released into two field sites in North Dakota between 1989 and 1991. Grasshoppers were collected over the summer at the field sites in 1992 and assessed for pathotype infection by cloned DNA probe analysis. The three most predominant grasshopper species that were infected ( Melanoplus sanguinipes, M. bivittatus and Camnula pellucida ) were assessed for pathotype infection with respect to their life stages (nymphal instars and adult males and females). Pathotype 1 predominantly infected grasshoppers in the subfamilies Oedipodinae and Gomphocerinae and pathotype 2 predominantly infected grasshoppers in the subfamily Melanoplinae. Early-instar M. sanguinipes and M. bivittatus had higher pathotype 2 infection frequencies, while late-instar and adult C. pellucida had higher pathotype 1 infection frequencies. Cross-infection by the pathotypes did occur in up to 3% of the individuals, on a per species basis, and primarily in later instar and adult grasshoppers. Pathotype 3 infections occurred in later instar and adults of the three grasshopper species. Infection of grasshoppers by E. grylli pathotypes is discussed with reference to the fungal life cycles.     

Metal loading and enzymatic degradation of fungal cell walls and chitin

The capacity of chitin (from crab shells) and of fungal cell walls from Trichoderma harzianum to accumulate zinc, cadmium and mercury was studied as well as the effects of adsorbed metals on the enzymatic hydrolysis by Novozym 234 of the two substrates. The total adsorbing capacity with respect to these metals was estimated to be at least 10 mmol kg^–1 chitin (dry weight) and 50 mmol kg^–1 fungal cell walls (dry weight), respectively, at pH 6.1. Enzymatic digestion of fungal cell walls preloaded with mercury and cadmium was significantly reduced, while zinc did not cause any significant inhibition. The effect of metal complexation by chitin on the enzymatic digestion was not as pronounced as for fungal cell walls. This could reflect the fact that chitin sorbed a lower total amount of metals. The inhibitory effect of metals on the enzymatic hydrolysis was caused by the association of the metals with the two substrates and not by the presence of free metals in solution.     

Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review

A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed.     

Stimulation of growth and glucose catabolite enzymes by succinate in some thermophilic fungi

Thermophilic Humicola lanuginosa, Penicillium duponti, Sporotrichum thermophile and Mucor pusillus required succinate in addition to glucose for optimal growth. The requirement for succinate was concentration-dependent and the concentration needed for one half of the maximal growth was 6.14 mM. In the presence of succinate, glucose utilization from the medium was markedly increased and this was associated with increased levels of the enzymes of the glycolytic and Krebs cycle pathways. Addition of succinate to cultures growing in glucose at any stage of growth stimulated the growth with the resulting rate of growth remaining high if the addition was made within 3 days of inoculation. Cycloheximide (71.4 M) prevented the succinate-mediated derepression of the enzymes suggesting that succinate may remove the catabolite repression in the presence of glucose.A preliminary part of this work was presented at the 17th annual meeting of the Association of Microbiologists of India at Manipal (India) held from Dec. 13 to 15, 1976