Symbiosis

Event Date: 
Wednesday, August 26, 2015 - 19:00 - 19:45
Institution: 
CSIRO
Title: 

The evolution of mutualistic trait variation in rhizobial symbionts across genetic and geographic scales

Abstract: 

Interactions between plants and nitrogen-fixing rhizobial bacteria are characterized by high genetic diversity for traits important to the outcome of the interaction at the population and species level. However, the selective processes underpinning the generation and maintenance of genetic and phenotypic variation in such interactions are not well understood. I will present an overview of data gathered from a series of experiments using interactions between Acacia spp. and their associated rhizobia, and that address questions regarding the ecological and evolutionary drivers of trait variation across different scales.  Specifically, I will discuss how 1) phylogenetic constraint; 2) within-species local adaptation; 3) nutrient availability; and 4) partner diversity and identity, influence patterns of specialization and community structure in legume-rhizobial mutualistic interactions. Our results suggest that both host-bacterial and bacterial-bacterial interactions are important for understanding evolutionary and ecological dynamics and highlight the importance of designing experiments that span different genetic and geographic scales.

Event Date: 
Wednesday, July 29, 2015 - 18:15 - 18:30
Institution: 
Australian Institute of Marine Sciences
Title: 

Coral Reefs Go Viral: Unveiling the viruses associated with corals in a changing climate.

Abstract: 

Viruses are the most common biological agents in the global oceans, with numbers typically averaging ten billion per litre. The ability of viruses to infect all organisms indicates they most likely play a central role in marine ecosystems and have important consequences for the entire marine food web. Marine viruses influence many biogeochemical and ecological processes, including energy and nutrient cycling, host distribution and abundance, and horizontal gene transfer events. Research into viruses associated with coral reefs is a newly emerging field. Corals form an obligate symbiotic relationship with the dinoflagellate genus Symbiodinium, upon which the coral relies heavily for nutrition and calcification. Disruption of this symbiosis can lead to loss of the symbiotic algae from their host, resulting in coral bleaching and, if the symbiosis cannot re-establish, death of the coral colony. While a number of factors, including elevated reactive oxygen species production by Symbiodinium have been linked to coral bleaching, viral infection has not been methodically examined as a possible cause. Viruses that potentially target the algal symbiont, Symbiodinium sp., have been reported previously; therefore, we examined whether Symbiodinium in culture is host to a virus that switches to a lytic infection under stress, such as UV exposure or elevated temperature. Analysis of algal cultures, using techniques including flow cytometry and transmission electron microscopy, revealed prevalent viral activity, regardless of experimental conditions. This talk will present recent results and results allow for the development of molecular diagnostic probes for rapid detection of viruses in field samples, and will help monitor and assess the role of viruses in coral bleaching and holobiont functioning.

Event Date: 
Wednesday, November 26, 2014 - 18:00 - 18:15
Institution: 
UWS
Title: 

Clues of sexual reproduction in the Arbuscular Mycorrhizal Fungi: a putatively ancient asexual land-plant symbiont

Abstract: 

Arbuscular Mycorrhizal Fungi (AMF) are an ancient group of obligate land-plant symbionts which form a mutualistic symbiosis with the roots of over 80% of land plants  and are found in the majority of terrestrial ecosystems. The filamentous hyphae of these fungi grow throughout the soil, scavanging for water and nutrients and transfer these to the plant in exchange for plant produced sugars.  As a result, extensive underground networks can form where multiple fungal individuals can be connected to a single plant and a single fungus can be connected to multiple plants simultaneously.  AMF do not have cells, rather nuclei flow freely through a common cytoplasm and genetically distinct individuals of a species are capable of anastomosis – or hyphal fusion – where cytoplasmic and nuclear exchange may occur. Curiously, these fungi have been once classified as ‘ancient asexuals’ due the lack of any observable sexual structures and an assumed purely clonal life-style. I present recent insights from the genome of the model AMFRhizophagus irregularis which contains evidence of a genetic tool kit which looks more like that of a sexually reproducing organism. I highlight the extreme expansion of a group of MATA-HMG genes which normally act as master- regulators of sex in fungi and present insights into the structure and function of these genes from a survey of local and global populations of R. irregularis individuals along with transcriptional evidence via QRT-PCR that a subset of these genes have a functional involvement in AMF partner recognition and possibly sexual reproduction.

Event Date: 
Wednesday, May 28, 2014 - 18:15 - 18:30
Institution: 
CSIRO
Title: 

Cairneyella

Abstract: 

In September 1999, I collected a small heath plant from a large sandstone outcrop near the Murphy’s Glen campsite in the Blue Mountains west of Sydney. This seedling had been growing in just a few centimetres of sand atop the rock. The shallowness of soil meant its root system was perpendicular to the stem, and spread out like a spider’s web from the base. Heath plants have unusual roots; they’re very fine, being only marginally thicker than a human hair. I took the plant back to the laboratories at University of Western Sydney and carefully cut these hair roots up in small pieces. I surface sterilised the pieces in bleach and placed each piece, numbered and its location in the root system recorded, onto an agar plate. From these tiny root pieces grew a host of very slow growing non-spore producing fungi. Most of these fungi were ericoid mycorrhizal (ERM) fungi – these fungi form a symbiosis with heath plants – facilitating their growth in challenging places such as acid bogs, nutrient poor sands and soils rich in metals such as cadium and zinc. Since 1999, I’ve undertaken quite a bit of work on the most abundant ERM fungus from this one seedling, and with the help of various collaborators we have observed the structures it forms in roots of heath plants, how it enhances the growth of heath seedlings and examined its carbon, nitrogen and phosphorus catabolism. It was, and still is, the most studied Australian ericoid mycorrhizal fungus. 
Upon moving to CSIRO in 2007, I left the last six cultures in the fridge in Dr. Peter McGee’s laboratory and it was here that they remained until 2013 when I retrieved them on Peter’s retirement. Just two of the last six survived the long winter. In late 2013, we had some space on an Illumina run with some other samples – and we sequenced the genome of this fungus. We’ve called it ‘Cairneyella’ after the late Professor John W. G. Cairney. There’s still much to learn about Cairneyella – and I’m seeking collaborators who’d like to share these last cultures and further the body of work on this remarkable fungus.

Event Date: 
Wednesday, November 27, 2013 - 18:00 - 18:15
Institution: 
Hawkesbury Institute for the Environment, UWS
Title: 

Organic phosphorus acquisition may be a functional driver of community structure for ectomycorrhizal fungi in a tri-partite symbiosis

Abstract: 

 
Alnus trees associate with ectomycorrhizal (ECM) fungi and nitrogen-fixing Frankia bacteria, and while their ECM fungal communities are uncommonly host specific and species poor, it is unclear whether the functioning of Alnus ECM fungal symbionts differs from that of other ECM hosts. We used exoenzyme root tip assays and molecular identification to test whether ECM fungi on Alnus rubra differed in their ability to access organic phosphorus and nitrogen as compared with ECM fungi on the non-Frankia host Pseudotsuga menziesii. At the community level, potential acid phosphatase (AP) activity of ECM fungal root tips from A. rubra was significantly higher than those from P. menziesii, while potential leucine aminopeptidase (LA) activity was significantly lower for A. rubra root tips at one of the two sites.  At the individual species level, there was no clear relationship between ECM fungal relative root tip abundance and relative AP or LA enzyme activities on either host. Our results are consistent with the hypothesis that ECM fungal communities associated with Alnus trees have enhanced organic phosphorus acquisition abilities relative to non-Frankia ECM hosts.  This shift, in combination with chemical conditions present in Alnus forest soils, may drive the atypical structure of Alnus ECM fungal communities. 

Event Date: 
Wednesday, July 31, 2013 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Genome evolution in Blattabacterium cuenoti

Abstract: 

In addition to harbouring intestinal symbionts, some animal species also possess intracellular symbiotic microbes. The relative contributions of gut-resident and intracellular symbionts to host metabolism, and how they coevolve are not well understood. Cockroaches and the termite Mastotermes darwiniensis present a unique opportunity to examine the evolution of spatially separated symbionts, as they harbour gut symbionts and the intracellular symbiont Blattabacterium cuenoti. The genomes of B.cuenoti from M.darwiniensis and the social wood-feeding cockroach Cryptocercus punctulatus are each missing most of the pathways for the synthesis of essential amino acids found in the genomes of relatives from non-wood-feeding hosts. Hypotheses to explain this pathway degradation include: (i) feeding on microbes present in rotting wood by ancestral hosts; (ii) the evolution of high-fidelity transfer of gut microbes via social behaviour. To test these hypotheses, we sequenced the B.cuenoti genome of a third wood-feeding species, the phylogenetically distant and non-social Panesthia angustipennis.We show that host wood-feeding does not necessarily lead to degradation of essential amino acid synthesis pathways in B.cuenoti, and argue that ancestral high-fidelity transfer of gut microbes best explains their loss in strains from M.darwiniensis and C.punctulatus.
 

Event Date: 
Wednesday, February 29, 2012 - 18:00 - 18:30
Institution: 
University of Western Sydney
Title: 

Microbial diversity and ecosystem functions, resilience & recovery: Beyond statistical correlation.

Abstract: 

Microbes are the most dominant and diverse group of organisms on planet Earth. They are pivotal to global ecosystem function, carrying out all critical biogeochemical cycling and directly or indirect shape the Earth’s climate. Despite this, their role is not explicitly considered in climate or ecosystem models. This is largely because of their enormous diversity and the lack of theoretical and experimental approaches to illustrate and quantify the magnitude of microbial regulation of ecosystem functions. There are a growing number of studies that provide evidence of the statistical relationship between microbial community and ecosystem function, but such approaches are unable to differentiate between the correlative and casual effects. In this presentation, using a novel diversity dilution approach, I will illustrate the direct role of microbial diversity and community composition in ecosystem function and sustainability, and argue for their explicit inclusion in predictive models.

Event Date: 
Wednesday, October 26, 2011 - 19:15 - 20:00
Institution: 
University of Queensland
Title: 

Sizing up the symbiotic partnership: towards a single-cell view of nutrients uptake in cnidaria-dinoflagellate symbiosis

Abstract: 

Reefs based on scleractinian corals are among the most productive and biologically diverse ecosystems on Earth. At the heart of their success as the architects of coral reefs, is their symbiosis with dinoflagellate algae, which live within their tissues and provide corals with an enlarged metabolic repertoire. Thus corals are ‘polytrophic’, being able to acquire carbon-based nutrients from sunlight through their algal symbionts (‘autotrophic’), feeding on plankton (‘heterotrophic’), and absorbing dissolved nutrients from the surrounding water. These strategies increase the nutritional options of corals in an environment where planktonic food supplies and dissolved nutrients in seawater may be episodic.

The intertwined nature of coral-dinoflagellate endosymbiosis has made the relative quantification of host and symbiont contributions to metabolic activities extremely difficult so far. Consequently, whilst we now recognize the threats of human activity, future climate change and associated symptoms of stress on the reef, very little is known about the nutritional function of the cnidarian-dinoflagellate symbiosis that underpins and maintains reef health.

In this talk, I will explore how the development of new technologies combining isotopic labeling and high resolution imaging analysis opens a new interdisciplinary frontier in the study of such symbiotic interactions with direct implications for how these organisms will respond to environmental changes.

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