Our 2011 seminar series has been kindly supported by the following organisations.
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Gene Cassette Products and Their Role in Vibrio Physiology: A Proteomics Approach
Vibrios are marine bacteria that are highly adaptable and subsequently capable of colonizing various niches. The integron/gene cassette system is a genetic element present in Vibrio spp., that incorporates mobile genes termed gene cassettes into a reserved genetic site via site-specific recombination. The integron consists of three basic elements: an integrase gene (IntI), an attachment site (attI) and a promoter (Pc). Gene cassettes contain an open reading frame and an IntI-identifiable recombination site called attC. Insertion (and excision) of gene cassettes is facilitated by an integrase-mediated recombination between attI and attC where cassettes can be accumulated forming a cassette array. Cassette arrays in Vibrio spp. are uniquely large, containing hundreds of contiguous gene cassettes. There is a consensus that these gene cassettes add to the adaptive potential of vibrios and have likely been an important driver in the evolution of vibrios into their respective niches. How this is achieved has been difficult to understand since 80% of gene cassettes are novel and consequently of unknown physiological function. Whole cell proteomic analysis comparing wild-type Vibrio rotiferianus DAT722 with isogenic mutants that have deletions in regions of their gene cassette array show the deletions have altered surface associated structures including extracellular polysaccharide and outer membrane proteins/porins. Studies into how the deletions impact the secretome/surfaceome are currently underway. This data aims to understand how the integron/gene cassette system drives Vibrio evolution by determining how these unique genes impact vibrio physiology.
Neosporosis: the nemesis of Australian fauna?
Neosporosis caused by an apicomplexan parasite Neospora caninum is a major protozoal reproductive disease in cattle and a recognised neurological disease in dogs. Currently, the majority of research on neosporosis has focused on cattle because the cattle industry identified the disease as a significant economic burden worldwide. However, virtually all vertebrates are assumed to be susceptible to neosporosis, with the degree of pathology varying between host species. Since no information exists on neosporosis in Australian native small marsupials, our aim was to provide evidence using experimentally infected animals. Our trial used Sminthopsis crassicaudata, the fat-tailed dunnart, a carnivorous marsupial widely distributed throughout the arid and semi-arid zones of Australia and one of only a few marsupial species bred in laboratory. The fat-tailed dunnart inhabits the same geographical areas as the dingo, feral fox and rangeland cattle, and, as its name suggests, its fat is stored in the tail, from a few millimetres from the base and almost to the tip. In contrast to existing models that develop relatively few N. caninum tissue cysts, dunnarts offer a new animal model in which active neosporosis is dominated by tissue cyst production. The results provide evidence for a sylvatic life cycle of N. caninum in Australia between marsupials and wild dogs. It establishes the foundation for an investigation of the impact and costs of neosporosis to wildlife.
The healthy human gut microbiota and how chemotherapy and antibiotics affect its composition.
Recent science associates the gut microbiota composition with the development of complex diseases such as for example cardio-vascular diseases, diabetes and inflammatory bowel diseases. Now, the human gastro-intestinal microbiota must be understood as a microbial organ whose metabolism provides essential functions to the host rather than just supplementary nutrient acquisition.
The first aim of this talk is to discuss what makes a “healthy” gut microbiota together with results from analysing vegetarian and elderly gut microbiota.
The second aim will be to discuss results from analysing the gut microbiota of people undergoing chemotherapy and antibiotics.
Whether (and how) diet and age affect the gut microbiota composition is not only really interesting; knowing the diversity of healthy gut microbiotas may help us to decide which composition to restore a perturbed microbiota to, for example after chemotherapy and antibiotic treatment.
Cheating, trade-offs and the evolution of virulence in a natural pathogen population
The evolutionary dynamics of pathogens are critically important for disease outcomes, prevalence and emergence. In this talk I will discuss some specific ecological conditions that promote the long-term maintenance of virulence polymorphisms in a pathogen population. Recent theory predicts that evolution towards increased virulence can be reversed if less virulent social ‘cheats’ exploit virulent ‘cooperator’ pathogens. However, there is little evidence that social exploitation operates within natural pathogen populations. I will demonstrate that for the bacterium Pseudomonas syringae, major virulence polymorphisms are maintained at unexpectedly high frequencies in the host Arabidopsis thaliana. Experiments reveal that the fitness costs of decreased virulence are eliminated in mixed infections, whereas less virulent strains have a fitness advantage in non-host environments. These results suggest that niche differentiation contributes to the maintenance of virulence polymorphisms, and that both within-host and between-host pathogen growth must be considered to understand the roles of cheating and cooperation in pathogen populations.
High Alpine Bacteria Display Strong Landscape Scale Distributions
Soil microorganisms dominate terrestrial biogeochemical cycles; however, we know very little about their spatial distribution and how changes in the distributions of specific groups of microbes translate into landscape and global patterns of biogeochemical processes. I use a nested sampling scheme at scales ranging from 2 to 2,000 m to show that bacteria from a high-alpine landscape have significant spatial autocorrelation in community composition up to a distance of 240 m. While this pattern is strongly predictable, the average diversity only increases by 5% across the entire landscape. This pattern is best explained changes in the relative abundance of specific bacterial clades in response to the soil environment across the landscape.
Genomics-guided discovery of novel traits in Pseudomonas fluorescens
Pseudomonas fluorescens is a diverse bacterial species known for its ubiquity in natural habitats and the production of structurally diverse, bioactive secondary metabolites. The high degree of ecological and metabolic diversity represented in P. fluorescens is reflected in the genomic diversity displayed among strains. Certain strains, such as the biological control bacterium P. fluorescens Pf-5, live in association with plants, protecting them from infection by plant pathogens. Strain Pf-5 produces an array of structurally-characterized secondary metabolites that are toxic to plant pathogenic bacteria, fungi and Oomycetes. Biosynthetic gene clusters for many of these metabolites are located in lineage-specific regions absent from the genomes of other strains of P. fluorescens. Orphan gene clusters, which encode for the biosynthesis of unknown natural products, have also been identified in lineage-specific regions of the Pf-5 genome and the following products identified through combined bioinformatic and chemical analyses. The novel cyclic lipopeptide orfamide A lyses zoospores produced by phytopathogenic Phytophthora spp. The FitD insect toxin contributes to the newly-discovered insecticidal activity of Pf-5, and several analogs of rhizoxin, a macrocyclic lactone, exhibit antifungal activity. Recently, orphan gene clusters expressed under the control of global regulators such as GacA have been identified via transcriptome analysis of Pf-5, demonstrating the value of global-regulator-based genome mining as an approach to decipher the secondary metabolome of Pseudomonas spp. We are also employing microarrays to gain a holistic view of genome expression profiles of Pf-5 living on seed surfaces, the environment where the bacterium interacts with seed-infecting fungi and Oomycetes to affect biocontrol. A series of Pf-5 mutants having deletions in one or many (up to seven) known or orphan gene clusters have been derived and are being tested in a series of bioassays. These approaches are providing new insights into the metabolic capacity of this bacterium, its activity on plant surfaces, and its interactions with plants, insects and other microorganisms.
How many microbiologists does it take to change a light bulb? None, as it turns out - the dozens of attendees at June's Joint Academic Microbiology Seminars (JAMS) at the Australian Museum waited patiently through a short blackout for drinks, snacks, and three servings of fresh scientific discussion.