Pseudomonadales

Event Date: 
Wednesday, October 29, 2014 - 18:15 - 18:30
Institution: 
UTS
Title: 

Stigmergic social behaviours facilitate the active expansion of Pseudomonas aeruginosa interstitial biofilms.

Abstract: 

Erin S. Gloag1, Awais Javed2, Huabin Wang3, Michelle L. Gee3, Scott A. Wade2, Lynne Turnbull1, Cynthia B. Whitchurch1*
1 The ithree institute, University of Technology Sydney, Ultimo, NSW, 2007, Australia.
2 Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia
3 School of Chemistry, University of Melbourne, Parkville, VIC, 3010, Australia.
 
Biofilms are often found associated with infections of implantable medical devices; accounting for approximately half of all nosocomial infections. Biofilms are often thought of as sessile surface-attached communities that are embedded in a protective slimy matrix. However, many bacterial pathogens also have the capacity to actively expand their biofilm communities via complex multi-cellular behaviours. We have observed that when P. aeruginosa is cultured at the interstitial surface between a coverslip and solidified nutrient media the resulting biofilm actively expands via twitching motility and is characterised by the formation of an extensive pattern of interconnected trails.
We set out to identify the factors governing pattern formation and coordinated movement during P. aeruginosa interstitial biofilm expansion. Our observations have revealed that during biofilm migration the cells at the advancing edge create furrows as they migrate across the semi-solid media The following cells are preferentially confined to these furrows, resulting in the emergence of an interconnected furrow network and the subsequent extensive large scale-patterning characteristic of these biofilms.
Stigmergy is a concept which describes self-organisation processes observed in higher organisms and abiotic systems through indirect communication via persistent cues in the environment left by individuals that influence the behavior of other individuals of the group at a later point in time. Our observations indicate that self-organised pattern formation in P. aeruginosa interstitial biofilms is also a stigmergic phenomenon. To our knowledge this is the first time that stigmergy has been identified as a mechanism of self-organisation of bacterial biofilms and propose that the concept of stigmergy can be included in the repertoire of systems used by bacteria to co-ordinate complex multicellular behaviours. We are currently exploring the development of novel antimicrobial strategies aimed at controlling and inhibiting biofilm expansion in medical settings via exploiting our new understanding of biofilm expansion.

Event Date: 
Wednesday, July 30, 2014 - 19:00 - 19:45
Institution: 
UTS
Title: 

The production of public goods in bacterial biofilms

Abstract: 

“Public goods” in bacterial communities are extracellular products that are released by a sub-set of individuals that provide benefits to the local population.  Extracellular DNA (eDNA) is a public good that has been found to be required for the formation of sessile biofilms by many species of bacteria including Pseudomonas aeruginosa.  We have recently shown that eDNA also facilitates the active expansion of P. aeruginosa biofilms by engineering the formation of a network of interconnected furrows and directing traffic flow throughout the furrow network to efficiently supply cells to the leading edge of the expanding biofilm. The mechanism by which eDNA is produced by P. aeruginosa and many other bacterial species is poorly understood. We have discovered a novel mechanism that accounts for the production of eDNA as well as other “public goods” in P. aeruginosa biofilms. 

Event Date: 
Wednesday, April 30, 2014 - 18:00 - 18:15
Institution: 
School of Biotechnology and Biomolecular Sciences UNSW
Title: 

The roles of extracellular DNA in bacterial biofilm formation

Abstract: 

Bacterial biofilm formation is dependent upon production of extracellular polymeric substances (EPS) mainly composed of polysaccharides, proteins, lipids and extracellular DNA (eDNA). eDNA promotes initial bacterial adhesion, aggregation, biofilm formation in a wide range of bacterial species. In Pseudomonas aeruginosa eDNA is a major component of biofilms and is essential for biofilm formation and stability. P. aeruginosa also produces phenazine an electrochemically active metabolite and phenazine production promotes eDNA release. The relationship between eDNA release and phenazine production is bridged via hydrogen peroxide (H2O2) generation and subsequent H2O2 mediated cell lysis and ultimately release of chromosomal DNA into the extracellular environment as eDNA. Recent investigation showed pyocyanin (a kind of phenazine predominantly produced by P. aeruginosa) binds to eDNA mediated through intercalation of pyocyanin with eDNA. Pyocyanin binding to DNA has significant impacts on DNA properties and also on P. aeruginosa cell surface properties including its hydrophobicity, attractive surface energies physico-chemical interactions and bacterial aggregation.

Event Date: 
Wednesday, September 26, 2012 - 18:00 - 18:15
Institution: 
Macquarie University
Title: 

Disruption of transporter genes in the enantio-pyochelin biosynthesis gene cluster of Pseudomonas protegens Pf-5 has pleitropic phenotypic effects

Abstract: 

 
Pseudomonas protegens Pf-5 is a biocontrol bacterium that produces the siderophore enantio-pyochelin under conditions of iron starvation which has the function of scavenging iron. In addition, biosynthetic intermediates of salicylic acid and dihydroaeruginoic acid are usually secreted as well. In this study, we tried to elucidate the roles of three putative transporters that are encoded by the genes PFL_3495, PFL_3503 and PFL_3504 via gene truncation experiments. Out of expectation, truncation of these genes resulted in increased secretion of these products in the culture supernatants. Transcriptional profiling revealed altered expression of the biosynthetic gene cluster by PFL_3504 mutant but not by the PFL_3495 and PFL_3503 mutants. Phenotype microarray revealed that these mutants have different stress and chemical resistance profile when compared to the wild-type. 

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.

 

An enthusiastic crowd of around 50 gathered to see out the winter months on the last day of August at another great JAMS meeting at the Australian Museum. The JAMS series brings together research microbiologists, including post-docs, PhD students and senior researchers, working in non-clinical projects from institutes throughout the Sydney region. The JAMS organisers would like to thank the Australian Museum for providing the fantastic venue for the meetings, as well as the Australian Society for Microbiology for sponsoring the event to provide pizza and drinks.

Event Date: 
Wednesday, August 31, 2011 - 19:15 - 20:00
Institution: 
Oregon State University
Title: 

Genomics-guided discovery of novel traits in Pseudomonas fluorescens

Abstract: 

Pseudomonas fluorescens is a diverse bacterial species known for its ubiquity in natural habitats and the production of structurally diverse, bioactive secondary metabolites. The high degree of ecological and metabolic diversity represented in P. fluorescens is reflected in the genomic diversity displayed among strains. Certain strains, such as the biological control bacterium P. fluorescens Pf-5, live in association with plants, protecting them from infection by plant pathogens. Strain Pf-5 produces an array of structurally-characterized secondary metabolites that are toxic to plant pathogenic bacteria, fungi and Oomycetes. Biosynthetic gene clusters for many of these metabolites are located in lineage-specific regions absent from the genomes of other strains of P. fluorescens. Orphan gene clusters, which encode for the biosynthesis of unknown natural products, have also been identified in lineage-specific regions of the Pf-5 genome and the following products identified through combined bioinformatic and chemical analyses. The novel cyclic lipopeptide orfamide A lyses zoospores produced by phytopathogenic Phytophthora spp. The FitD insect toxin contributes to the newly-discovered insecticidal activity of Pf-5, and several analogs of rhizoxin, a macrocyclic lactone, exhibit antifungal activity. Recently, orphan gene clusters expressed under the control of global regulators such as GacA have been identified via transcriptome analysis of Pf-5, demonstrating the value of global-regulator-based genome mining as an approach to decipher the secondary metabolome of Pseudomonas spp. We are also employing microarrays to gain a holistic view of genome expression profiles of Pf-5 living on seed surfaces, the environment where the bacterium interacts with seed-infecting fungi and Oomycetes to affect biocontrol. A series of Pf-5 mutants having deletions in one or many (up to seven) known or orphan gene clusters have been derived and are being tested in a series of bioassays. These approaches are providing new insights into the metabolic capacity of this bacterium, its activity on plant surfaces, and its interactions with plants, insects and other microorganisms.

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.

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