Cycloheximide resistance in the Lipomycetaceae revisited

Cycloheximide (CYH) is a heterocyclic, glutarimide antibiotic that is a potent inhibitor of protein biosynthesis in most eukaryotes. This study demonstrated that yeasts from all species of the Lipomycetaceae, with the exception of Dipodascopsis spp., can grow in the presence of up to 5 g·L–1 CYH — a concentration that is five times higher than the accepted “highest” concentration of 1 g·L–1 used in physiological tests for yeast identification. Lipomycetaceous yeasts are known to utilize heterocyclic nitrogen-containing compounds such as thymine as sole nitrogen source. CYH contains a glutarimide ring, which is chemically similar to thymine. We investigated the possibility that CYH resistance in the Lipomycetaceae might be due to an ability to degrade CYH and use it as the sole nitrogen source. However, we were unable to demonstrate significant growth on CYH as sole nitrogen source. When thymine was used as positive control, we could demonstrate its utilization as sole nitrogen source.

Immunocontraceptive Effects on Female Rabbits Infected with Recombinant Myxoma Virus Expressing Rabbit ZP2 or ZP3

Recombinant myxoma viruses expressing rabbit zona pellucida 2 (rZP2) or rabbit zona pellucida 3 (rZP3) glycoproteins were constructed and tested in domestic rabbits to assess their potential to induce autoimmune infertility. The recombinant virus expressing rZP2 had no effect on fertility or ovarian histology, despite all animals developing antibodies against the rZP2 antigen. However, recombinant viruses expressing rZP3 induced infertility in 70% of animals at the first breeding. Serum antibodies were relatively short-lived, but antibody was bound to zona pellucida of all rabbits from Day 10 onward. There was no obvious correlation between infertility and rZP3 antibody titer. There was a transient inflammatory response in the ovaries of rZP3-immunized rabbits at Day 15 but no T-cell response to rZP3 could be detected at any time. Dysfunctional follicular formation was present in ovaries from rabbits infected with rZP3-expressing viruses 15-40 days postinfection but this had disappeared at later time points. A recombinant myxoma virus expressing a modified rZP3 antigen with the C-terminal hydrophobic putative anchor sequence deleted was also tested. This virus did not induce either infertility or an antibody response against the zona pellucida. Thus, the context of antigen presentation was crucial for an autoimmune response.

Prevalence of serum antibodies to canine adenovirus and canine herpesvirus in the European red fox (Vulpes vulpes) in Australia

OBJECTIVES

To determine the seroprevalence and aspects of the epidemiology of canine adenovirus (CAdV) and canine herpesvirus (CaHV-1) in European red foxes (Vulpes vulpes) in Australia.

DESIGN

Serum samples were collected opportunistically from foxes in 1991-1994 in Western Australia (WA) and South Australia (SA) and in 1980-1984 and 1990-1994 in New South Wales (NSW) and the Australian Capital Territory (ACT). The sera were examined for antibody to CAdV and CaHV-1 using ELISAs. Seroprevalence in the different regions was determined for both viruses and the CAdV data were analysed for interactions between decade of collection, age, season, region and gender using logistic regression.

RESULTS

The overall prevalence of antibody to CAdV was 23.2% (308/1326) but was significantly higher in sera collected in the eastern states of Australia (47%: 233/498) than in WA (9%: 75/828). Overall, in NSW and the ACT, there was a significantly lower prevalence in juveniles than in adults and the prevalence in juveniles in the 1990s was significantly lower than in the 1980s. The prevalence was also significantly lower in the autumn than in the winter for juveniles but the reverse held for adults. The NSW and ACT data were subdivided into eastern (including the ACT) and western regions. This revealed a significantly higher prevalence in the winter than in the autumn for the west and the reverse in the east. In WA, the northern rangeland regions of WA had lower prevalence (1.9%) than the southern agriculture regions (10.7%). Seasonally, there was a peak prevalence in the spring dropping through the summer and autumn and rising again in the winter. This seasonal pattern was also found in the combined data for all sites in the 1990s. There was no gender difference in prevalence of CAdV either overall or in different regions. The overall prevalence of antibody to CaHV-1 was 2.2% (28/1300). The small number of positives allowed only limited statistical analysis that did not reveal any differences in decade of collection, age, season or region.

CONCLUSIONS

CAdV infection is common in the Australian fox population whereas CaHV-1 infection is rare. For CAdV, the age and seasonal patterns of seroprevalence were generally consistent with the recruitment of young susceptible foxes into the population in the spring and the accumulation of infections with age. The differences in regional prevalences correlated with fox density. The low prevalence of antibody to CaHV-1 suggests that CaHV-1 may be a more suitable vector than CAdV for bait delivery of immunocontraceptive antigens to foxes in Australia.

Integrated shrub management in semi-arid woodlands of eastern Australia: ground and aerial application of defoliant to shrubs regenerating after disturbance

This paper describes experiments undertaken at several sites in semi-arid woodlands of eastern Australia to determine if chemicals applied either on the ground or from the air reduce the density of shrubs regenerating after disturbance. Ground-spraying of Roundup® in the autumn was more effective than spring application in defoliating shrubs, especially 2-year-old coppice growth. Spraying of Roundup with a hand-held boom at 0.5 up to 2.5 kg glyphosate/ha identified rates to be used for boom spraying. Aerial spraying experiments were then undertaken across several sites and involved several target species. The location of sufficiently large areas where shrub regeneration was of an optimum age (i.e. about 2–3 years) proved to be extremely difficult due to prevailing drought conditions precluding the use of prescribed fire as a preliminary treatment. Nonetheless in one experiment, young (1-year-old) regrowth of firebush (Senna pleurocarpa) exhibited increased sensitivity to Roundup with significant shoot mortality recorded after it had been applied at 0.5 kg glyphosate/ha. Aerial spraying based on an ultra-low volume application of 10 L/ha further enhanced cost-effectiveness on this occasion. Economic analyses structured around 20-year partial budgeting and determination of net present value (NPV) suggested a profitable return could be expected where treatment was based on Roundup applied at this threshold rate 2 years after a prescribed fire, especially when the rehabilitation costs were spread over an entire paddock that had been only partially sprayed. Finally, operational aspects involving aerial spraying in these semi-arid woodlands are also discussed.

Death model for tussock perennial grasses: a rainfall threshold for survival and evidence for landscape control of death in drought

We investigated relationships between rainfall (and landscape, zonation and nearby grazing disturbance) and the death rates of four perennial grass species in a highly functional semi-arid wooded grassland in eastern Australia. Two grasses were palatable C3 species (Monachather paradoxa Steud. and Thyridolepis mitchelliana (Nees) S. T. Blake) and two were unpalatable C4 species (Aristida jerichoensis (Domin) Henr. var. subspinulifera Henr. and Eragrostis eriopoda Benth.). During the 10-year study the grasses were protected from large herbivore grazing within paddocks continuously grazed by sheep. Death occurred only during droughts and rates of death were species-dependent. When plotted against several water availability indices, rainfall and rainfall/evaporation during the preceding 3 months provided best predictions of death. Longer preceding periods gave inferior predictions. A 3-month rainfall total of 75 mm and a 3-month rainfall/evaporation ratio of 0.15 were survival critical thresholds below which deaths began. The 3-month rainfall totals, rainfall/evaporation and estimated water status of plants were equally reasonable predictors of deaths, but were inconsistent in their effectiveness. Rainfall was adopted for the grass death model; death begins when 3-month rainfall total declines below a threshold of 75 mm and the death rate rises with lower rainfall. Position of plants in the gently undulating landscapes influenced water status and, hence, death rates. Water status of grasses on the two water-shedding zones and the ‘flat’ zone were similar at each assessment, but higher on ‘ridge run-on’ and ‘toe-of-slope’ zones. Foliage height and diameter also influenced death rate but were species dependent. Basal diameter did not influence death rate. Survivorship of several perennial grass species at widely spaced sites in south-eastern Australia provided equivocal support for generality of the grass death model.

Statistical models for the effect of age and maternal antibodies on the development of rabbit haemorrhagic disease in Australian wild rabbits

Statistical models have been developed to explain the influence of age and maternal antibody on the outcome of rabbit haemorrhagic disease virus (RHDV) infection of Australian wild rabbit kittens in terms of survival, survival time in those that failed to survive, and pyrexia (temperature response, or fever). Similar models describing survival and survival time were derived by substituting mass for age, owing to their high correlation. The models were developed from data obtained following the inoculation of 78 kittens 5–11 weeks old born to does with varying levels of α-RHDV immunoglobulin (IgG) antibody as measured by enzyme-linked immunosorbent assay (ELISA). A significant correlation was found between survival and doe titre but not between survival and kitten titre. It was deduced that maternal antibody in kittens can fall below the level of detection in the ELISA but still be protective. The model describing the influence of age and doe titre had the form logit(SURVIVAL) = 5.98 – 0.944(AGE) + 0.000473(DOE TITRE), and showed, for example, that kittens born to seronegative does had a 50% probability of survival at about 6 weeks old and, with a doe titre of 10 240, a 50% probability of survival at about 11 weeks old. There was a significant influence of kitten titre on pyrexia, and the model developed had the form logit(TEMPERATURE RESPONSE) = 1.436 – 0.0531(KITTEN TITRE). The influence of age and maternal antibody on survival time was fitted using Cox proportional hazard models. A parametric regression gave rise to a final model of the form S(t | AGE, DOE TITRE) = exp[–(t/ηAGE)1.7979], where ηAGE = exp[7.1838 – 0.2976(AGE) + 0.000227(DOE TITRE)]. The model showed that survival time decreased with age, but for each age category there was an increase in survival time with increasing doe titre. Kitten titre had only a marginally significant effect on seroconversion; there was no effect of kitten age or mass, or of doe titre. No kitten with a titre of 60 or more seroconverted.

Crop productivity in relation to species of previous crops and management of previous pasture

An experiment at Rutherglen in north-eastern Victoria compared 5 grass-removal methods in subterranean clover-based pastures that were grown before cropping sequences of canola–wheat–lupin–wheat or wheat–wheat–lupin–wheat. The cropping sequences were started in 3 successive years to provide replication in time. Grass removal from the pasture was more effective in winter than in spring and led to yield increases by the first and second crops. The largest increase (80%) was by the first canola crop after winter-cleaned pasture. The yield increase by the equivalent wheat crop was 42%. Since annual grasses and canola do not host the same root pathogens, we conclude that the yield responses were not due to root-disease control but probably to increased N supply. Assays of wheat roots confirmed that root disease was negligible throughout the experiment. Wheat growing in the year after canola yielded 11% more than wheat growing after wheat. The most surprising result was a 17% increase in the yield of wheat growing 3 years after canola compared with wheat growing 3 years after wheat, with wheat–lupin sequences in the intervening years for both systems. We suggest that canola and lupin, both of which are non-hosts of arbuscular mycorrhizal fungi, reduced mycorrhizal root colonisation in the fourth-year wheat crop, leading to less drain on assimilates.

The effect of buprenorphine on the course of disease in laboratory rabbits infected with myxoma virus

The only method of assessing the virulence of myxoma virus is to record survival times of rabbits inoculated with the virus. This raises ethical concerns about using animals in experiments where death is the end point. We investigated whether or not the opioid analgesic buprenorphine could be used in rabbits without compromising the myxoma virus virulence assay and on the presumption that animals may suffer pain during the course of the disease. Thirty, 5-month-old New Zealand White rabbits were divided into two groups stratified for weight and gender, and inoculated intradermally with 100 pfu of the Standard Laboratory Strain (SLS) of myxoma virus. At day 6 post infection (p.i.), when eyelid swelling was first seen, each animal in one group was treated with 0.03 mg/kg buprenorphine, subcutaneously, morning and evening until death. Animals in the other group were untreated. Animals were weighed daily and rectal temperatures taken morning and evening. Intake of food and water was assessed as was general demeanor including respiratory effort. There was no significant difference in mean survival time, weight change, or demeanor between the two groups. Increased respiratory effort was seen from day 10 p.i. in animals surviving up to and beyond that time but again there was no difference between groups. Animals treated with buprenorphine refused food and water a day earlier than untreated animals, and had lower temperatures immediately prior to death. It was concluded that the opiate analgesic buprenorphine can be used without compromising the current virulence assay for the SLS of myxoma virus in New Zealand White rabbits but that the clinical signs of myxomatosis that could be attributed to pain were not abrogated.

Prevalence of viral antibodies and helminths in field populations of house mice (Mus domesticus) in southeastern Australia

A 13-month study of wild mice (Mus domesticus) in wheatlands in southeastern Australia contrasted changes in the seroprevalence of antibody to 13 viruses and the occurrence of helminths with changes in their population dynamics. Mice were seropositive for mouse hepatitis virus (MHV), rotavirus, minute virus of mice (MVM), mouse adenovirus (MAdV), reovirus (reo 3), and murine cytomegalovirus (MCMV). The seroprevalences of all but rotavirus varied significantly with time and increased with host density. Near the end of the study, host density declined rapidly and the seroprevalence of MVM and reo 3 increased significantly. These two viruses had low seroprevalence when host survival was high and high seroprevalence when host survival was low, indicating they may play a role in regulating mouse populations. In the case of MVM, there was evidence of a viral epizootic during the decline in mouse abundance. The prevalence of four helminths (Taenia taeniaeformis, Syphacia obvelata, and Vampirolepis spp.) differed significantly with time but showed no apparent association with host density. These findings highlight the need for further study on the effect of viruses on the population dynamics of mice.

Multiline varieties and disease control : 6. Effects of selection at different stages of the pathogen life cycle on the evolution of virulence

Existing theoretical models have led to conflicting predictions concerning the likely effect of the widespread use of dirty crop multilines on the evolution of virulence in pathogen populations. Here we attempt to clarify these problems by extending existing models to include selection against unnecessary genes for virulence at two different stages in the life cycle of the pathogen. The results of these studies indicate that the stage of the life cycle at which selection occurs can significantly influence the evolution of virulence in pathogen populations growing on multiline varieties.

Phenotypic Variation and Plasticity in the Colonizing Species Xanthium Strumarium L. (Noogoora Burr)

Levels of genotypic (O'G 2) and environmentally induced (O'E2) variation for 15 quantitative characters were estimated in seven populations of the four naturalized races of X. strumarium in Australia. Estimates of O'G2 indicated that populations of X. strumarium were often genetically variable for quantitative traits. However, for the majority of the characters studied, O'E2 was a larger component of the total phenotypic variation than was O'G 2 , indicating that phenotypic plasticity is the major mode of adaptation of this species to variable and varying environments. Few significant differences were found among the races, or among populations within a race, in either O'G2 or O'E2. This suggests that marked differences in colonizing ability of the four races of X. strumarium are probably not .due to differences in phenotypic plasticity (individual buffering) or genotypic variation (populational buffering) but to differences in such factors as their reproductive strategies and photoperiodic requirements for flowering.