Biomedical subjects

P Jeffries

Publications and source records attributed to P Jeffries.

8 recordsLinked to original sources

PubMed2002

Phenotypic degeneration occurs during sector formation in Metarhizium anisopliae.

AIMS: The formation of sectors was observed during subculturing of an isolate of the entomopathogenic fungus Metarhizium anisopliae, a fungus used for biological control of insect pests. The aim of the investigation was to establish whether sector formation was accompanied by changes in physiological characters. METHODS AND RESULTS: Four degenerative morphological states, with reduced sporulation capacity, were characterized. Subcultures were taken from each sector and four new culture lines established. The new lines were further subcultured every 21 d. A physiological assessment of each line was undertaken after 42 d using TLC of secondary metabolites and fluorogenic enzyme tests. Full sporulation capacity was not regained on subculture, although some cultures recovered partially. Changes in secondary metabolite profiles and the loss in detection of activity of specific enzymes were observed. CONCLUSIONS: Sector formation was frequently accompanied by changes in the ability to produce secondary metabolites and enzymes. SIGNIFICANCE AND IMPACT OF THE STUDY: The results illustrate the importance of maintaining the stability of important cultures during routine subculture. The consequences could have significant implications if degenerate cultures are used as inocula for liquid fermentation cultures or industrial scale production.

Enzymes↗

PubMed2001

Ribotyping of rhizobia nodulating Acacia mangium and Paraserianthes falcataria from different geographical areas in Indonesia using PCR-RFLP-SSCP (PRS) and sequencing.

Acacia mangium and Paraserianthes falcataria are leguminous tree species widely grown for timber in Indonesia and other tropical countries, yet little is known about the identity of their rhizobial symbionts. Polymerase chain reaction-restriction fragment length polymorphism-single-strand conformational polymorphism (PRS) analysis of the 16S rRNA gene was used along with sequencing to assess the diversity of 57 rhizobia isolated from nodules of A. mangium and P. falctaria in Indonesia. In total, 26 rhizobia isolated from A. mangium were analysed by PRS and sequencing. The PRS patterns indicated that 12 (46%) clustered with Bradyrhizobium elkanii, 13 (50%) with B. lianoningense/japonicum and one (4%) with Mesorhizobium loti. Thirty-one isolates were analysed from P. falcataria: five (16%) clustered with B. elkanii and 26 (84%) with B. lianoningense/japonicum. These results were confirmed by phylogenetic analysis of sequences. Intraspecific diversity of the 16S rRNA genes from rhizobia nodulating A. mangium and P. falcataria revealed by PRS was low, only one genotype was found within the isolates that clustered with B. elkanii and two within the B. liaoningense/japonicum group. These Bradyrhizobium species are apparently ubiquitous throughout the Indonesian archipelago and it is clear why the two tree species are able to successfully establish outside their native range without the need for inoculation with indigenous rhizobia.

Acacia↗

PubMed2001

Management of indigenous plant-microbe symbioses aids restoration of desertified ecosystems.

Disturbance of natural plant communities is the first visible indication of a desertification process, but damage to physical, chemical, and biological soil properties is known to occur simultaneously. Such soil degradation limits reestablishment of the natural plant cover. In particular, desertification causes disturbance of plant-microbe symbioses which are a critical ecological factor in helping further plant growth in degraded ecosystems. Here we demonstrate, in two long-term experiments in a desertified Mediterranean ecosystem, that inoculation with indigenous arbuscular mycorrhizal fungi and with rhizobial nitrogen-fixing bacteria not only enhanced the establishment of key plant species but also increased soil fertility and quality. The dual symbiosis increased the soil nitrogen (N) content, organic matter, and hydrostable soil aggregates and enhanced N transfer from N-fixing to nonfixing species associated within the natural succession. We conclude that the introduction of target indigenous species of plants associated with a managed community of microbial symbionts is a successful biotechnological tool to aid the recovery of desertified ecosystems.

Desert Climate↗

PubMed1994

Production of antibacterial compounds by phylloplane-inhabiting yeasts and yeastlike fungi.

The production of antibacterial compounds by yeasts and yeastlike fungi isolated from the phylloplane is reported. Aureobasidium pullulans, Citeromyces matritensis, Cryptococcus laurentii, Rhodotorula glutinis, and Sporobolomyces roseus produced antibacterial compounds inhibitory to both Pseudomonas fluorescens and Staphylococcus aureus in an overlay bioassay. In contrast, isolates of Candida albicans, Filobasidium uniguttulatum, Saccharomyces cerevisiae, Torulaspora delbruckii, Tremella foliacea, Trichosporon beigelii, and Trichosporon dulcitum obtained from soil or from culture collections did not produce inhibitory compounds when screened by the same procedure. The production of antibacterial compounds was examined in more detail, using several isolates of A. pullulans distinguished by cluster analysis on the basis of biochemical and physiological tests. They were found to produce a range of antibacterial compounds with different activities. Two distinct antibiotics were produced by an isolate of A. pullulans in liquid culture during both the logarithmic and the stationary phases of growth.

Anti-Bacterial Agents↗

PubMed1985

Changes occurring in chloroplasts of Phaseolus following infection by Sclerotinia: a cytochemical study.

Dramatic changes occur in the ultrastructure of chloroplasts within host tissues during the infection of Phaseolus by the plant pathogenic fungus Sclerotinia. Electron-opaque deposits develop initially in the peripheral region of the chloroplast stroma, in cells in advance of the hyphal front. As infection continues, the amount and intensity of deposition increases and spreads throughout the chloroplast. The deposits possess a high degree of structural integrity in the form of a crystalline square lattice with 10 nm periodicity. Enzyme digestion studies have been used to show that the deposits are proteinaceous. Similar deposits are also induced by treatment with oxalic and citric acids, but not by the potassium salts of these acids buffered at pH 7.2. It is suggested that a pH change within the chloroplasts, resulting from oxalic acid secretion by the fungus, is responsible for induction of protein deposition. The likelihood that the deposits are ribulose, 1,5-bisphosphate carboxylase-oxygenase is discussed.

Ascomycota↗

PubMed1976

Physiology and fine structure of sporangiospore germination in Piptocephalis unispora prior to infection.

Germination of the sporangiospore of Piptocephalis unispora Benjamin, observed by means of light and electron microscopy, involved the formation of a new inner wall which became continuous with the inner layer of the wall of the germ tube. The outer wall layer of the germ tube was continuous with the original inner wall layer of the dormant spore. Preliminary details of appressorium structure were noted. Nutritional experiments indicated that sporangiospores required external sources of utilisable nitrogen and carbon compounds for maximal swelling and germ tube production. Limited development occurred when either nutrient was supplied singly. Comparison of germination of the asexual spore with that in other Mucorales, especially the Kickxellaceae, has been made, and the merosporangial status in P. unispora discussed.

Caseins↗

PubMed1975

Ultrastructure of the sporangiospore of Piptocephalis unispora (Mucorales).

Sporangiospore structure in Piptocephalis unispora Benjamin was studied using light microscopy, freeze-etching, scanning and transmission electron microscopy, and compared with that of other members of the Mucorales. A merosporangial wall, plasmalemmal invaginations, and wall protuberances were demonstrated in sections and their possible significance discussed.

Cell Wall↗

PubMedDate not supplied

Developing cryopreservation protocols to secure fungal gene function.

Protocols that involve a freezing process are frequently used for the preservation of fungi, but there have been few studies to assess the physiological and genetic stability of isolates after preservation. In this study, the effects of cryopreservation and lyophilisation on the viability, physiology and genetic stability of isolates of Metarhizium anisopliae, Fusarium oxysporum and Serpula lacrymans were examined. It was found that preservation regime influenced the characters of some of the test isolates. Secondary metabolite profiles and extracellular enzyme production can be affected by preservation. Polymorphism's were detected after PCR fingerprinting in replicates of 2 isolates of Metarhizium that had been preserved by cryopreservation and lyophilisation. The results indicated a need to improve existing preservation protocols. Research is being undertaken to develop novel cryopreservation regimes for recalcitrant micro-organisms. Biochemical and molecular techniques will be used to assess the effectiveness of preservation.

Cell Survival↗