November 2014

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, 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, November 26, 2014 - 19:00 - 19:45
Institution: 
UNSW
Title: 

“The microbial friends and foes of seaweeds”

Abstract: 

 

Seaweeds (macroalgae) form a diverse and ubiquitous group of photosynthetic organisms that play an essential role in many aquatic ecosystems, yet till recently very little was understood with respect to their associated microbiota. We now know that macroalgae are home to a diverse community of microorganisms, that display both temporal and spatial variation yet remain distinct from the surrounding seawater. Symbiotic interactions between marine microorganisms and macroalgae can have both positive (e.g. providing nutrients and morphogenic cues or protection from biofouling) and negative (e.g. disease) outcomes for the host. This talk will give an overview of the microorganisms typically associated with macroalgae with a focus on the bacterial symbionts. Details of how bacteria successfully colonize macroalgal hosts will be discussed with specific examples of the functional role of microbial epiphytes in macroalgal health (including disease) highlighted from a “holobiont” perspective.