University of Sydney

Event Date: 
Wednesday, August 29, 2012 - 19:00 - 20:00
Institution: 
University of Sydney
Title: 

The distribution of Phytophthora in the Greater Blue Mountains WHA.

Abstract: 

 
Disease caused by Phytophthora cinnamomi is becoming increasingly prevalent within the Greater Blue Mountains World Heritage Area (GBMWHA), yet little is known of the distribution of pathogens or the impact of disease. An understanding of the disease distribution is required to develop management strategies in natural ecosystems like the GBMWHA. However where only sporadic information is available, conservation efforts may be limited by incomplete sampling for pathogen presences due to remoteness and inaccessibility of many sites. Risk models can overcome some of these drawbacks. Hence, we modelled the distribution of P. cinnamomi in the GBMWHA by combining landscape and environmental information using a GIS approach. Data layers were reclassified into risk layers using FUZZY logic such that localities conducive to dieback were given the highest risk rating enabling the compilations of a relative risk surface. The area identified with the highest risk was the Blue Mountains National Park primarily due to optimal temperatures for pathogen development, known infestations and an abundance of roads, tracks and paths To investigate the range of Phytophthora infestation soil sampling was conducted based on the risk levels in the model using a stratified random approach. Results indicate the pathogen is widespread across the WHA. However, infestation is sporadic with negative samples occurring frequently. Isolations were more common in areas of greater human activity, such as the highly visited Blue Mountains National Park. Results also implicate vehicles in anthropogenic dispersal. Further testing is being undertaken to improve our understanding of the pathogen-environment-disturbance relationship and genetic analysis of isolates will explore inter and intraspecific species variation. Information gained from the survey will allow managers to prioritise hygiene and quarantine measures, and facilitate the development of ecological models of the distribution of Phytophthora within the GBMWHA. 

Event Date: 
Wednesday, June 27, 2012 - 19:15 - 20:00
Institution: 
Faculty of Agriculture & Environment, University of Sydney, Sydney, NSW.
Title: 

Sulfur cycling in the rhizosphere: the role of sulfatase and sulfonatase diversity.

Abstract: 

Growth of healthy, high-yielding crop plants requires a stable input not only of nitrogen and phosphorus, but also of sulfur (S). Although S is naturally present in soils, it is usually bound in organic form as sulfate esters or sulfonates, which are not directly bioavailable to plants. Sulfur can be supplemented by addition of inorganic fertilizer, but most sulfate for plant nutrition is provided by microbial turnover of organically-bound sulfur. To identify the rhizosphere organisms responsible for this turnover, we focused on the key genes atsA, which encodes arylsulfatase, and asfA, which is required for aryldesulfonation. Functional T-RFLP analysis was used to analyse atsA diversity in a range of agricultural and natural soils, and clear atsA community differences associated with land use and soil/bedrock types were observed, which were mirrored in the arylsulfatase activity of the cultivable fraction of the population. Soil arylsulfatase activity is routinely assayed as a measure of soil health, but these data highlight the need for detailed studies on arylsulfatase gene diversity in the soil. Sulfonatase diversity was measured in rhizospheres of field-grown wheat plants and in a sulfate-limited Agrostis-dominated grassland, and the effect of adding sulfate in long-term or short-term treatments was tested. Functional asfA community analysis showed that desulfonation genes from both wheat and Agrostis rhizospheres were dominated by Variovorax and Polaromonas species. This distribution of taxa was also found in a cultivation-dependent analysis, and these genera appear to be key players in rhizosphere sulfonate transformations in several environments. Increasing our understanding of the rhizosphere microbes that catalyse soil organosulfur turnover will allow us to develop management practices to maximize soil sulfur availability, and minimize the costs associated with fertilization.

Event Date: 
Wednesday, May 30, 2012 - 18:15 - 18:30
Institution: 
University of Sydney
Title: 

A proteomic interrogation of flagellum function

Abstract: 

The eukaryotic flagellum is involved in an array of biological processes and is implicated in an ever-growing spectrum of inherited human disease. Trypanosoma brucei, the causative agent of sleeping sickness in humans, produces a single flagellum that is essential in many critical aspects of cell biology and pathogenicity. Here we employ a combined approach utilising reverse genetics and comparative proteomics to interrogate the protein composition of the paraflagellar rod, an accessory structure of the trypanosome flagellum that is required for correct flagellum function. We have identified more than twenty novel components and confirmed the localisation of a large test set by epitope tagging. This discovery process was iterated to identify at least two co-dependent sub-groups of proteins. The protein domain characteristics of the sub-groups suggest a link between calcium sensing and adenine nucleotide homeostasis in the paraflagellar rod which has wider implications for the regulation of flagellum function generally.

Event Date: 
Tuesday, April 24, 2012 - 18:15 - 18:30
Institution: 
University of Sydney
Title: 

Factors affecting insect-associated bacterial communities

Abstract: 

Like all animals, insects harbor bacteria that influence host traits. The factors affecting insect-associated bacterial assemblages have historically been difficult to study due to limited sampling, but recent technological advances in microbial ecology (namely, bar-tagged pyrosequencing) permit the characterization of hundreds of microbial communities. I used this approach to explore insect-associated bacterial communities in three separate studies: 1) Flea-associated bacteria across space, time, and species; 2) Aphid-associated bacteria across space, diet, and host species; 3) Insect-associated bacteria from 87 unique insect species. Results suggest that communities differ among insect species and that communities shift across space and time within insect species.

Event Date: 
Wednesday, March 28, 2012 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Genetically controlled network architecture in the filamentous fungus Neurospora crassa constrains amino acid translocation

Abstract: 

Effective nutrient translocation in fungi is essential for nutrient cycling, mycorrhizal symbioses, virulence and substrate utilization. An interconnected mycelial network is proposed to influence resource translocation, but has not been empirically tested. By comparing amino acid translocation in Neurospora crassa colonies defective in network formation and translocation between wild type colonies of different developmental ages, we can gain insight into the influence of network formation on nutrient translocation.

Event Date: 
Wednesday, January 25, 2012 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Vaccinia Virus BTB-Kelch Proteins and the Ubiquitin-Proteasome System during poxvirus infection.

Abstract: 

Vaccinia virus (VACV)—the live-virus vaccine used to eradicate smallpox (Variola virus)—encodes three BTB-Kelch protein (BBK) orthologues, a family of cellular proteins that have demonstrated roles in the Ubiquitin-Proteasome System (UPS). The UPS is the common mechanism by which specific proteins are degraded at specific times inside the host cell. Substrate proteins are multiply-ligated with ubiquitin and are thus flagged for degradation by the 26S Proteasome. If an invading virus were to commandeer such a system it may be rewarded with a unique and powerful solution to avoid the intrinsic cellular defences. BBKs function as UPS substrate adaptors, acting as a link between the ubiquitination machinery and the ubiquitin-ligated substrates themselves.

By encoding BBKs VACV can hijack the UPS and selectively degrade a wide range of host proteins to its advantage; preventing the establishment of an antiviral immune response, transforming the cell into a virus-production factory or enhancing viral spread. Manipulation of the UPS is a phenomena known to play a role in mediating infection in many other viral contexts. The identification of VACV BBK substrates may highlight new mechanisms by which VACV and other viruses overcome the intrinsic cellular defences to mediate infection.

We have previously shown, using fluorescently tagged BBKs, partial colocalisation with the ubiquitinylation machinery, indicating that these proteins act via a common UPS-based mechanism. These results are consistent with partial redundancy observed in BBK mutants and the obstructive effect of UPS inhibitors on poxvirus replication. We are now attempting to further elucidate any potential interactions and dissect the global implications of poxviral interactions with the UPS.

Event Date: 
Wednesday, November 30, 2011 - 18:15 - 18:30
Institution: 
University of Sydney
Title: 

The fungal secretome and virulence: analysis of the proteins secreted by Cryptococcus gattii strains with different virulence profiles.

Abstract: 
Cryptococcus gattii is a ubiquitous environmental yeast-like fungus capable of causing disease in a wide range of animal hosts. In humans, disease progression begins after inhalation of the infectious propagule leading to infection of the lung. The infective yeast cells can then disseminate to the central nervous system, resulting in meningoencephalitis, which can be fatal if left untreated.

Closely related strains of C. gattii exhibit significantly different degrees of virulence in the mammalian host. Fungi utilize absorbtive nutrition and produce a range of secreted degrative enzymes, and as these may invoke a host response, the fungal secretome is likely to be very important in modulating the host-pathogen interaction. In this study, we compare the secretomes of two C. gattii strains, one categorized as hypervirulent (R265) and the other exhibiting low-level virulence (R272). C. gattii was grown under conditions designed to be as similar as possible to those encountered in vivo. Secreted proteins were captured from the culture supernatant by re-circulating across ProteominerTM beads using a closed peristaltic pump system. Concentrated protein was analysed via 1D nanoLC-MS/MS. A total of 27 proteins were identified with only four protein identifications being shared by both strains. The secretome of R265 primarily included uncharacterized proteins containing catalytic cores with roles in carbohydrate degradation as well as the antioxidant superoxide dismutase and a GTPase. R272 secreted a more diverse set of proteins including enolase and transaldolase, enzymes canonically involved in glycolysis and the pentose phosphate pathway respectively, but both also described as fungal allergens that bind IgE.

This work indicates that very different cohorts of proteins are secreted by closely related strains of C. gattii exhibiting different levels of virulence. By enhancing our understanding of the fungal secretome and unraveling these differences it may suggest novel therapeutic strategies or help devise diagnostic markers predicting for disease progression.
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