Hospitality

Event Date: 
Wednesday, February 25, 2015 - 18:00 - 18:30
Institution: 
San Diego State University
Title: 

Integrating microbial community dynamics into kelp forest ecosystem models

Abstract: 

Metagenomics has enabled a greater understanding of microbial community dynamics than previously realized and now the challenge is to integrate microbial dynamics into ecological models. My lab takes an ‘omics approach mixed with classical microbiology to identify factors affecting microbial communities and how an altered microbial community will affect macro-organism health and ecosystem functioning. The key habitats are coral reefs and kelp forests. Within the kelp forest, we have started with a culturing approach that has identified novel genomes associated with the giant kelp Macrocystis pyrifera. Phenotypic assessments of these bacteria have identified increase in the microbe’s ability to tolerate copper and resist antibiotics with increasing human activities. We have tested the effects of altered microbial abundance and community composition on survival and development of M. pyrifera gametophytes. Decreasing microbial abundance enhanced M. pyrifera recruitment, increasing zoospore settlement and gametophyte development. Gametophytes reared in microbial communities sampled adjacent to the populated city showed lower survival and growth compared to gametophytes in microbial communities from a remote island. Metagenomics revealed a high abundance of phototrophic and oligotrophic microbes from the island, compared with an abundance of eutrophic microbes adjacent to the city. In addition, microbes adjacent to the city lacked genes that produce quorum signaling molecules, negatively influencing kelp spore settlement. Long term analyses of the microbial communities from the kelp forest have been initiated and we are currently investigating the microbes associated with the water column and kelp surface at two distinct depth. First, at 0.5 m depth where the water is warmer, highly oxygenated and receiving large amounts of carbon from photosynthesis and second, at 15 m depth where the water is under seasonal thermocline, colder, lower in oxygen, and can potentially be exposed to high partial pressure of carbon dioxide. Monthly sampling has revealed microbial number is lower at depth and pCO2 is higher. Metagenomic analysis of these samples is under way. Kelp feeds the ecosystem through degradation and we are currently investigating the effects of microbes on kelp degradation and subsequent nutritional value. We have shown altered microbial communities are detrimental to kelp recruitment and are identifying way of adding these data to ecosystem models.

Event Date: 
Wednesday, November 26, 2014 - 18:15 - 18:30
Institution: 
QAAFI
Title: 

Plant Cell Wall Breakdown in Complex Ecosystems

Abstract: 

Plant cell walls in e.g. whole grains, fruits and vegetables are a major source of dietary fibre (DF) in human diets. Cellulose is a key DF component, and its fermentation in the large intestine also contributes to the extent of nutritional benefits to the host. However our understanding of which microbes actively ferment cellulose in the complex gut environment is minimal. Here we report on the use of isotopically-labelled cellulose as a route to defining microbial fermentation in a complex ecosystem. The ability of the Gram-negative, obligately aerobic, rod-shaped bacteriumGluconacetobacter xylinus, to produce extracellular cellulose in simple fermentation experiments, in the presence of a 13C-labelled carbon source, was exploited to make isotopically labelled cellulose. Scanning electron microscopy (SEM) and nuclear magnetic resonance spectroscopy (NMR) showed no differences in micro-architecture and crystallinity between native and isotopically labelled bacterial cellulose. Fermentability was assessed by an in vitro batch culture system, where anaerobic fermentations with either a pig faecal slurry or minimal medium with a 1: 5 diluted pig faecal inoculum were carried out.  The gas production kinetics was recorded and end-products were analysed. Results indicated that 13C did not alter the fermentability of bacterial cellulose. We are now carrying out DNA-stable isotope probing coupled with high-throughput sequencing, to provide direct information on which microbes from the porcine faecal inoculum actively ferment the substrates. Ultimately, combining such studies will identify mechanisms of plant cell wall breakdown in the human nutritional context and allow for the understanding of gut microbiota responses to molecularly-defined dietary changes.

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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