Microbial Pathogenesis and Biodiversity
Dr. Miguel Valvano, Dr. André Lachance, Dr. Greg Thorn
This program integrates medical microbiology with microbial biodiversity and soil science as outlined below.
From the soil to human pathogenesis
The Biotron's integration of soil scientists, microbiologists and earth scientists will enable an enhanced understanding of the origins of human pathogens and their progression from the soil to human diseases. The pathogenicity (i.e. the ability to cause disease) of inherently multi-drug resistant bacteria have become a health threat. For example, usually harmless while surviving in the soil, the bacterium, Burkholderia cepacia (B. cepacia), can cause devastating infections in patients with diseases such as cystic fibrosis (CF). This pathogen is also found in sporadic outbreaks of severe infections among hospitalized patients. The Biotron's Valvano group exploits B. cepacia as a model pathogen to investigate multi-drug resistance in a typical soil bacterium that can cause human infections in a compromised host. A Tier 1 Canada Research Chair has been awarded to Dr. Valvano for his pioneering research into multi-drug resistance.
The pathogenesis of B. cepacia is not well understood. A major hurdle in gaining a better understanding of its pathogenicity is the relative paucity of suitable genetic tools and reagents for use in this bacterium. The Valvano lab has recently developed new cloning and expression vectors that facilitate genetic research in B. cepacia. The Valvano lab has also discovered that isolates of B. cepacia can survive within amoebae and macrophages.
Remarkably, intracellular survival occurs without evident bacterial replication. This feature sets B. cepacia apart from other well studied intracellular pathogens that can replicate within infected cells. Intracellular survival of B. cepacia thus provides us with a model system to investigate bacterial persistence in a host. B. cepacia is one of the few bacteria known to display a formidable intracellular resistance to all classes of cationic peptides. The Valvano group hypothesizes that the inherent intracellular resistance of B. cepacia to cationic peptides may be due to selection pressures in its natural soil habitat. They will address this hypothesis by characterizing in detail the molecular basis of resistance of B. cepacia to cationic peptides and characterize the role of cationic peptide resistance for the survival of this organism in its host and in the soil. This work is significant and innovative as it will provide experimental evidence demonstrating that the same properties required for bacterial survival in the soil also determine the bacterium's ability to function as an opportunistic pathogen upon infection of a susceptible host.
In other bacteria like Salmonella, Escherichia coli, Erwinia, and Pseudomonas aeruginosa, the resistance to cationic peptides results from adaptation to magnesium (Mg2+)-limiting environments. Preliminary evidence from the Valvano group indicates that a regulatory response in B. cepacia is mounted in the presence of high concentrations of antibiotics, like tetracycline, and that this response is exerted through a functionally analogous system that responds to low Mg2+. Thus, this group will focus their research on studying the genetic and functional basis of cationic peptide resistance in B. cepacia, its regulation, and its potential role in bacterial survival in experimental models of infection as well as in the soil. The Valvano lab has recently isolated 118 mutants of B. cepacia that are unable to survive in vivo. To test the hypothesis that survival in the host and in the soil has common features, the mutants will be assessed for survival in different types of soil, and under different environmental conditions. While important and innovative discoveries have been made by the Valvano group, the present limitation to these experiments is the current lack of a controlled and contained soil environment of sufficient scale and capacity for experimental expansion. The Earth Sciences and the Microbiological Facilities present in the Biotron will enable this ground-breaking research.
Microbial molecular ecology and biodiversity
The Biotron�s Microbial Facility coupled with the scale and environmental control within the mini-ecosystems will enable researchers to make unprecedented progress in understanding the impact of global warming on microbe-insect-plant interactions.
Under natural conditions, our biosphere is homeostatic or in balance with respect to energy and nutrients, in part, because of the complex interactions between the diverse species that populate it. Each plant, animal, insect and microbial species within this complex web plays a role in the maintenance of global homeostasis. Climate change as well as current agricultural and forestry practices are having and will continue to have a significant impact on biodiversity. Understanding the underlying basis for the complex interactions that maintain this biodiversity as well as establishing the sensitivity and impact of climate change, agriculture and forestry on these interactions is integral to sustain long-term ecosystem health.
The long-term sustainability of both the agriculture and forestry industries in Canada and throughout the world is critically dependent on maintaining microbial biodiversity. A mandate of the Biotron is to accelerate our understanding of the ecological impact of current forestry and agriculture practices, and enable researchers to determine the effects of natural and human disturbance on microbial biodiversity and soil ecosystem health. This research on biodiversity that is enabled by scale and controlled environment flexibility of the Biotron and its partners will be critical in setting national and international policies with respect to biodiversity and will have far-reaching impacts on current management practices on two of Canada's largest industrial sectors: agriculture and forestry. This research integrates the Microbial Facility and the Earth Sciences Facility in Module 1 with the research on sustainable plant productivity in Module 2. Furthermore, this research will exploit the interactive scale and climate control available in the form of the unique mini-ecosystems in Module 1.
The yeast-insect-plant model is an ideal model to study the complexity of ecosystem biodiversity, Dr, Lachance's group and their international collaborators are world leaders and pioneers in applying this model to global microbial biodiversity.
Their approach combines traditional microbiological and ecological techniques with recent advances and progress in DNA sequence technology to assess and unravel the complex interdependence of microbe, insect and plant on an ecological scale. It is clear from their research that yeasts play a critical role in the biological interface between insects and plants. A primary goal of this international research group is to elucidate the role of yeasts in this complex synergy between microbe, insect and plant host.
Lachance�s research group hypothesizes that one critical physiological characteristic that appears to dictate the geographic distribution of yeasts is their cardinal growth temperature, that is, their minimum, maximum and optimal growth temperatures. The complexity of this unique, communal interaction is exacerbated by the fact that the insect vectors also exhibit geographical distributions that are dependent upon their own cardinal growth temperatures, Clearly, one long-term effect of global warming is the change in the microbial flora and fauna of a region associated with wild and domesticated plants and animals.
The complex interactions between yeast, insects and plants have been neglected experimentally due to inadequate facilities with respect to scale and environmental flexibility. The Biotron dramatically increases scientific capacity by providing facilities for multi-kingdom studies under specified, controlled and contained environment conditions. First, the Biotron includes a unique national and international laboratory facility for the characterization of the largest number of living yeast specimens in the world through an extensive bank of thermoregulated incubators coupled with a high-capacity cryogenic storage system for long-term preservation of yeast specimens. Second, the Biotron's mini-ecosystem facility will enable the design of experiments aimed at explaining the interactions between yeasts, insects and plant hosts as well as the impact of climatic changes in temperature, humidity and CO2 concentrations on microbe-insect-plant interactions.
In the face of global climate, it is essential to understand how current agricultural and forestry practices affect soil microbial communities. The primary goal of Dr. Thorn's research is to determine the impacts of disturbance by different agricultural practices and forestry operations, on the diversity and ecosystem function of soil fungi, especially a group known as the basidiomycetes. These fungi are critically important within an ecosystem because they are the primary organisms responsible for the decomposition and nutrient cycling of plants. Thorn hypothesizes that disturbance due to agricultural and forestry practices affect the make-up and diversity of fungal communities and that the greatest soil fungal biodiversity will occur in sites of intermediate disturbance. The results of these experiments will help to answer the vital question of whether disturbance eliminates particular species of fungi that are important to soil health such as soil aggregation and the decomposition of plant litter. Through a combination of traditional and molecular techniques, previously unknown fungal diversity will be detected and identified in order to ink soil ecosystem functions such as soil aggregation and plant litter decomposition to the diversity that is discovered. Through a CFI New Opportunities Grant, Dr. Thorn and collaborators have established a state-of-the-art facility for microbial molecular ecology. The knowledge gained through this research will be integral in sustaining crop and forest productivity in a changing global climate.
The Biotron will provide the necessary facilities to not only culture and preserve newly discovered species of soil fungi but the presence of the mini-ecosystem facility will provide the capacity to examine the potential impact of climate change associated with global warming such as increases in temperature CO2 concentrations and decreased water availability on soil ecosystem health and, in turn, the impact altered soil ecosystem health on natural vegetation as well as crop productivity. This research will be integrated with the research on sustainable crop productivity (Hüner/Grodzinski) as well as soil microbe pathogenesis (Valvano) described above, by examining the effect of transgenic plant growth and decay on soil yeast and fungi respectively. To our knowledge, this level of integration is rarely if ever attained due to the lack of research facilities which can provide both the necessary scale and the required flexibility with respect to controlled environment conditions. The Western/Guelph Biotron Facility will enable such integration.
