Pseudomonas

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. 

JAMS Meeting Report – April 2012
by Thomas Jeffries
 
There was a good turnout on ANZAC day eve for three interesting talks, pizza and free local beer.
 
Kicking off the evening was John Lee, from the University of Georgia, with his ambitiously titled talk “Bioluminescence: The First 3000 Years”.  After a historical introduction to the long running observation of bioluminescence, via the discovery in 1672 that oxygen was necessary for bacterial luminescence, John told us how it was determined that bioluminescence is an enzyme mediated chemical reaction involving “luciferase” and "luciferine". In the modern age of biochemistry it was determined that ATP is the substrate in this reaction.  Following the elucidation of the structure of firefly luciferase in 1959, modern techniques (i.e. picosecond dynamic fluorescence spectroscopy and NMR) have allowed researchers to uncover the enzymes and processes involved in bioluminescence.  One of the most important of these enzymes Green-fluorescent protein (GFP) was discovered in jellyfish by Shimomura (who evidently has a lab at his house!) and led to his Nobel prize in 2008.  Due to GFP’s widespread use in research, it is regarded as one of the most important proteins in science.
 

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.

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.

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