July 2014

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, July 30, 2014 - 18:00 - 18:15
Institution: 
UTS
Title: 

Exploring coral-bacteria interactions: where are they, how do they get there and what do they do?

Abstract: 

Microorganisms live in tight ecological associations with corals, but microbial community composition, functions and behaviours within coral reef ecosystems are not yet fully understood. To examine the community structure, metabolic capacity and the potential role of chemotaxis in the ecology of coral reef bacterial communities, we performed a suite of laboratory, in-situ and thermal stress experiments on Heron Island, the Great Barrier Reef (GBR). To characterise patterns in microbial composition and metabolic capacity across different niches on a coral reef, metagenomes were sequenced from seawater samples associated with the surfaces of corals, the sandy substrate and in open water, outside of the reef. Within these environments we also examined the potential ecological role of chemotaxis among coral associated bacteria, by using laboratory and in situ chemotaxis assays to test for levels of chemotaxis towards several chemoattractants known to be released by corals and their symbiotic dinoflagelletes including amino acids, carbohydrates, ammonium chloride, and dimethylsulfonopropionate (DMSP). Finally, to determine how environmental variability, specifically thermal stress, influences bacterial community composition, behaviour and metabolic capacity, manipulation experiments were conducted using Pocillopora damicornis in flow-through aquatic systems on Heron Island.
 We found that the composition and metabolic potential of coral reef bacteria is highly heterogeneous across a coral reef ecosystem, with a shift from an oligotroph-dominated community (e.g. SAR11, Prochlorococcus, Synechococcus) in the open water and sandy substrate niches, to a community characterised by an increased frequency of copiotrophic bacteria (e.g. Vibrio, Pseudoalteromonas, Alteromonas) in the coral seawater niches. Among the major functional patterns observed were significant increases in genes associated with bacterial motility and chemotaxis in samples associated with the surfaces of coral colonies. These patterns were directly confirmed by chemotaxis experiments, which demonstrated that bacteria associated with the surfaces of the corals exhibited high levels of chemotaxis, particularly towards DMSP and several amino acids. Levels of chemotaxis by coral-associated bacteria were consistently higher than those demonstrated by non-coral associated bacteria. The phylogenetic composition of the chemotactic microbes, determined using 16S rRNA amplicon pyrosequencing, differed to the background community in the surrounding seawater, and incorporated several known coral-associated bacteria, Rhodobacteraceae, Flavobacteriaceae, Pseudomonadaceae and included potentially pathogenic Vibrios. Notably many of these bacteria, specifically Rhodobacterales, Flavobacterales and Vibrionales also became the dominant coral associated organisms under conditions of thermal stress experiments, indicating that these copiotrophic and chemotactic bacteria become key colonisers of thermally stressed corals.
Taken together our data demonstrate that coral reef bacterial communities are highly dynamic and that key groups of copiotrophic bacteria have the capacity to use sensitive chemotaxis to exploit nutrient gradients and potentially locate their coral hosts. Under conditions of heat stress, these behaviours may allow pathogenic organisms to locate and infect compromised hosts. 

Event Date: 
Wednesday, July 30, 2014 - 18:15 - 18:30
Institution: 
Macquarie University
Title: 

Effect of Low Temperature on Tropical and Temperate Isolates of Marine Synechococcus.

Abstract: 

An abundant and globally occurring marine picocyanobacterium, the genus Synechococcus is an important player in oceanic primary production and global carbon cycling. In the complex marine environment, this widespread organism has evolved to successfully colonize and inhabit different environmental niches. Their biogeographic distribution suggests that Synechococcus ecotypes exhibit thermal niche preferences. Temperature is a key environmental variable and the elucidation of the temperature stress acclimation in members of this genus can shed light on the molecular mechanisms involved in their adaptive capability. The growth of four representative Synechococcus isolates of various ecotypes from tropical and temperate regions were monitored under various temperature conditions. This revealed drastic differences in growth rates in correlation with their thermal niche preferences. The temperate strains CC9311 and BL107 displayed higher growth rates at lower temperatures while tropical strains WH8102 and WH8109 grew better at higher temperatures. In order to further elucidate their thermal niche preference, the molecular factors influencing the temperature-related growth patterns were explored through global proteomic analysis of WH8102 and BL107. Whole cell lysates of the strains grown at different temperature conditions were fractionated using 1D SDS-PAGE and analysed using label-free quantitative proteomics. Protein identifications provided 27% and 40% coverage of the whole genome for WH8102 and BL107, respectively. Quantitation of protein expression revealed 22% and 20% of the identified proteins were differentially expressed in WH8102 and BL107, respectively. The results were further investigated using qRT-PCR and PAM fluorometry. Differential expression revealed that low temperature appeared to have a significant effect on the photosynthetic machinery. The light harvesting components, phycobilisomes exhibited a reduced expression which could be the result of protein degradation due to photo-oxidative damage and/or as a mechanism to restore the energy balance disturbed as a consequence of low temperature. The lowered phycobilisome expression is found to be a common low temperature-related response between the tropical and temperate isolates. Within the photosynthetic reaction centres, differences in the expression of some core proteins were observed between the two isolates. The expression of core proteins could correlate with the efficiency of repair mechanisms involved in the replacement of photo-damaged core proteins. This differential expression sheds light on the underlying factors which potentially influence the differences in the thermal ranges of tropical and temperate isolates.

Event Date: 
Wednesday, August 27, 2014 - 18:00 - 18:15
Institution: 
USyd
Title: 

Bowel movement: resistance plasmid transfer in the gut

Abstract: 

The treatment of endogenous infections caused by commensal Escherichia coli are often complicated by antibiotic resistance. Strains of resistant E. coli in the gastrointestinal tract serve as a reservoir of resistance determinants, and dissemination of resistance genes is often facilitated by conjugative plasmids. It is important to understand these plasmids in order to track the movement of resistance determinants between populations.
 
Three faecal E. coli isolates from a healthy adult were examined. Two of these (838-98B and -3B) were resistant to ampicillin (Ap), streptomycin (Sm) and sulphamethoxazole (Su). The other (838-50A) was susceptible. 838-50A and -3B were indistinguishable by biochemical and molecular analysis (API20E, phylogenetic group PCR, RAPD). 838-98B was a distinct strain. B/O plasmid replicons were detected in both resistant isolates using PCR-based plasmid replicon typing. A B/O replicon was not detected in the susceptible strain. This suggested that a plasmid bearing a B/O replicon might be responsible for ApSmSu resistance. Conjugation experiments with a laboratory adapted E. coli strain (UB5201) confirmed that the movement of a B/O plasmid from both 838-98B and -3B conferred ApSmSu resistance. Plasmid sequencing revealed that an identical B/O plasmid, p838B-R (94.8kb), was present in 838-98B and -3B, and carried ApSmSu resistance determinants. p838B-R was also observed to mobilise small plasmids, allowing the direction of in situ transfer to be determined.
 
The observed transfer of antibiotic resistance plasmid p838B-R between two unrelated strains in the gastrointestinal tract highlights the important role commensal bacteria play in the spread of resistance determinants. While not well documented, the association of B/O-type plasmids with antibiotic resistance is evident not only through p838B-R but also other available plasmid sequences. Further studies will allow us to determine the extent to which these plasmids influence antibiotic resistance in commensal E. coli

Event Date: 
Wednesday, August 27, 2014 - 18:15 - 18:30
Institution: 
UNSW
Title: 

Analysis of gene co-expression networks reveals mechanisms underlying synergistic antifungal treatment in S. cerevisiae

Abstract: 

 
Background: Fungal pathogens are difficult to treat. There are few effective antifungal drugs available, and resistance is emerging. Iron chelators are promising synergents due to the importance of iron availability during host infection, but the mechanistic role of antifungal-chelator combinations is poorly understood. The project analyses cellular pathways that are differentially expressed during the synergistic response to elucidate the mechanisms and targets of drug-chelator treatment.
Method: To measure the effect of synergistic treatment on the S. cerevisiae transcriptome, cells were treated with i) amphotericin B only; ii) a combination of amphotericin B + lactoferrin, an iron chelator; and iii & iv) corresponding matching controls. RNA-seq data were generated using Illumina HiSeq 2000 with biological triplicates multiplexed and randomized across two sequencing lanes. Differential expression analyses were performed using EdgeR, and the results were co-visualized with biological networks using Cytoscape.
Results: Amphotericin B alone resulted in the down-regulation of nine genes involved in ergosterol biosynthesis and the up-regulation of AFT1, a transcription factor involved in iron transport. Amphotericin B + lactoferrin co-treatment halted AFT1 up-regulation and down-regulated genes involved in iron transport. These genes were co-expressed with YAP5, a second transcription factor that co-ordinates the expression of genes that control the nuclear localization of AFT1 and also governs the expression of oxidative stress response genes.

Event Date: 
Wednesday, August 27, 2014 - 19:00 - 20:00
Institution: 
Macquarie University
Title: 

"Xenbiotics and Xenogenetics: Human Influence over Microbial Evolution"

Abstract: 

The extent of human effects on planetary and biological processes means that we are now the world’s greatest evolutionary force. Perhaps the best example of human driven selection is the rapid evolution of antibiotic resistance in a wide range of bacterial pathogens. Continued antibiotic use has resulted in the assembly of complex DNA molecules composed of diverse resistance determinants and mobile elements, each with independent phylogenetic origins. These novel plasmids, transposons, integrons and genomic islands are xenogenetic, in that they have arisen in human-dominated ecosystems as a direct result of human activity. Xenogenetic elements are being released via human waste streams along with significant quantities of selective agents and other xenobiotic compounds, creating environmental reactors that foster even more complex interactions between genes, mobile elements and diverse bacterial species. Saturation of the environment with selective agents is also likely to increase the basal rates of mutation, recombination and lateral gene transfer in all bacterial species. Consequently, the antibiotic revolution may now be having unintended, second order consequences that will affect the entire microbial biosphere.

It was nice to see the JAMS crowd infultrating the ASM conference in Melbourne. As people prepare to migrate north for ISME in Korea don't forget to come into the Australian Museum for a taste of local microbiology offerings.

A big thanks to everyone who turned up to celebrate Microbiology at the Australian Museum last night. With 70 people in attendance (including a contingent from Osaka Prefectural Semboku High School) the pizza and drinks didn't last long. Jessica Tout (JAMS annual symposium JPP poster prize winner 2014) and Deepa gave excellent presentations before we were treated to a visual spectacular by Cynthia Whitchurch resolving the inner workings of biofilm biology and public good release by bacteria. Thanks also to Tim Williams and Sabrina Beckmann for running pizzas and beers for the event. Finally, if you're keen to help out at the JAMS desk during the Australian Museum Science Festival plese contact Ani Penesyan (anahit.penesyan@mq.edu.au). Glorious. See you in August.