Gram negative bacteria

Event Date: 
Wednesday, May 30, 2012 - 18:00 - 18:15
Institution: 
UNSW
Title: 

Deep sequencing of evolving populations in bacterial biofilms

Abstract: 

 

Bacterial communities growing as biofilms are subject to a distinct lifecyle, featuring initial surface attachment, microcolony formation and dispersal of cells. Bacterial biofilms are sometimes characterised by high levels of heritable phenotypic variants, presumably resulting from genetic diversification during the biofilm lifecyle. As biofilms are a favoured lifestyle of many environmental and pathogenic bacteria, identifying the evolutionary processes responsible for this diversification has important implications, both for our understanding of ecological processes, such as niche adaptation, and to clinically relevant questions, such as the evolution of antibiotic resistance.
I've used longitudinal genome-wide deep sequencing to reveal the underlying genetic structure of bacterial populations growing as biofilms, for the model organisms Phaeobacter gallaeciensis 2.10 (an abundant marine bacterium) and Pseudomonas aeruginosa 18A (a clinical Cystic Fibrosis isolate). Biofilms were grown under defined laboratory conditions known to generate reproducible phenotypic diversification. Samples from different stages of biofilm development were then sequenced to very high coverage (>800x). By accounting for sequencing errors using a matched-sample approach, variants with population frequencies as low as 0.5% could be accurately identified.
In general, the extent and nature of genetic variation was comparable for biofilms of both model organisms, being driven by selection for a small number of non-synonymous variants within key genes involved in biofilm- and competition-related pathways. These results also demonstrate that genome-wide deep sequencing can rapidly, accurately and comprehensively describe genetic variation within evolving populations.

 

Event Date: 
Tuesday, April 24, 2012 - 19:15 - 20:00
Institution: 
Nanyang Technological University, Singapore / UNSW
Title: 

The Great Escape: Biofilm formation and dispersal

Abstract: 

Bacteria form biofilms on almost all surfaces, ranging from ship hulls to cooling towers, to indwelling biomedical devices.  Biofilms also play positive roles, for example, floc and granule formation for the biological remediation of contaminated water.  Therefore, there is strong drive to understand the processes of biofilm formation, to either eliminate biofilm formation in some industrial processes and human health, or to encourage their formation, for processes such as remediation.  To develop innovative, environmentally friendly, biofilm control technologies, it is essential to understand the process of biofilm formation and how bacteria control the process of dispersal. 
Bacteria rapidly respond to changes in nutrient conditions, and we have shown that depletion of nutrients, e.g. carbon limitation or nitrogen, can lead to dispersal of bacterial biofilms.  This process is mediated via an intracellular second messenger cascade, using cAMP and c-di-GMP and may also be linked to other physiological signals such as nitric oxide mediated dispersal. 
We have also shown that biofilm development and dispersal is dependent on a prophage carried by Pseudomonas aeruginosa.  The phage plays an important role in multiple aspects of biofilm development and stability and we are beginning to unravel the mechanisms result in phage conversion which ultimately are linked to biofilm development.

Event Date: 
Wednesday, August 31, 2011 - 18:00 - 18:15
Institution: 
CSIRO
Title: 

Cheating, trade-offs and the evolution of virulence in a natural pathogen population

Abstract: 

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.

Event Date: 
Wednesday, April 27, 2011 - 18:00 - 18:15
Institution: 
Maquarie University
Title: 

Transcriptome led microbial discovery.

Abstract: 

Using a genome wide transcriptomic approach, Karl was able to unravel the role of the Pseudomonas global
activator system (GacA/GacS) in the regulation of an extremely broad range of functions including iron acquisition, oxidative stress response, secondary metabolism and motility. Similar work in Acinetobacter baumannii, a bacterium that is emerging as a major human pathogen due to multiple drug resistance, has revealed the antibiotic efflux to be major mode of resistance and led to the discovery of novel resistance proteins. Karl is a post-
doctoral fellow at Macquarie University working in Prof. Ian Paulsen’s group.

Event Date: 
Wednesday, February 23, 2011 - 18:00 - 18:15
Institution: 
UTS
Title: 

Class 1 integrons in genomic islands of pathogenic Pseudomonas aeruginosa isolates.

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