Microbiology

Event Date: 
Wednesday, March 27, 2013 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Insight into the specificity of Wzx for O-antigen processing

Abstract: 

Most Gram-negative bacteria have an O antigen that consists of repeats of 3-6 sugars, and serve as an essential factor for host colonization in many disease-causing bacteria. Until now, most known O antigens are assembled by the Wzx/Wzy pathway. This involves the assembly of repeat units within the cytoplasmic face of inner membrane on a lipid carrier, undecaprenol-phosphate, which are translocated across membrane by the Wzx translocases. In the periplasmic face, the repeat units are polymerized by the Wzy polymerase, and then subsequently ligated to preformed lipid A-core in the periplasm. Earlier works have shown Wzx translocases have a relax specificity requirement over the repeat-unit structures. However, this could neither correlate to the presence of O antigen with defined structures in each respective bacteria, nor could it explain the biological diversity of Wzx translocases. Our data show that Wzx translocases have a serotype specificity over their native repeat-unit structures, and provides evidence that the earlier conclusion were obscured by protein overexpression. This provides relevant explanation to the presence of highly diverse, yet structurally defined bacterial surface polysaccharides in nature.

Event Date: 
Wednesday, January 30, 2013 - 19:00 - 19:30
Institution: 
University of NSW
Title: 

Who’s doing what? A metaproteomic survey of Southern Ocean microbes near Antarctica.

Abstract: 

The ocean around Antarctica is not just cold, it’s also dark for a large part of the winter.  This means that carbon fixation by photosynthesis is inhibited during the polar winter.  We used metaproteomics to reconstruct the ecology of microbes at the surface of the Southern Ocean near the Antarctic Peninsula, for both winter and summer seawater samples.  Metagenomics (community genomics) tells us what kinds of genes are present.  Metaproteomics goes a step further and determines which proteins (including enzymes) are actively being produced by microbes within a community.  Therefore, we can use this approach to reconstruct microbial processes used for carbon fixation, nutrient acquisition, and other metabolic pathways.  We found that ammonia-oxidising archaea were dominant at the Southern Ocean in winter, with the detected proteins indicating that they had a major role in ‘dark’ (light-independent) carbon fixation at the surface.  In summer, by contrast, these autotrophic archaea were undetectable at the ocean surface, when photosynthesis by algae was the major route of carbon fixation.  SAR11 bacteria (Pelagibacter spp.) were prevalent in both winter and summer, and detected proteins indicate that ATP-dependent uptake was important for the acquisition of nutrients by these heterotrophs, including simple organic compounds such as amino acids and taurine.  Flavobacteria (especially Polaribacter) were more prevalent in summer, and the detected proteins show that these heterotrophic bacteria use exoenzymes to target complex biomolecules (polypeptides, polysaccharides) released from decaying algae.  Overall, metaproteomics of the Southern Ocean surface has allowed us to identify the similarities and differences between winter and summer microbial communities, as well as which particular nutrients are being targeted by individual groups of bacteria and archaea.

Event Date: 
Wednesday, January 30, 2013 - 18:15 - 18:30
Institution: 
University of Western Sydney
Title: 

Changes in soil microbial community precede changes in plant community along a chronosequence

Abstract: 

Shrubs in semiarid ecosystems facilitate the establishment of other plant species under their canopies and promote changes in these understory plant communities as they grow. To better understand whether plant community dynamics are linked to changes in soil microbes, we characterized soil microbial communities in gaps (interspaces) and under Retama sphaerocarpa shrubs of three different size/age classes. Different methodological approaches including pyrosequencing of 16S rDNA, phospholipid-fatty acid (PLFA) analysis and microbial activity indicators were combined to characterize both the structure and function of microbial communities along the chronosequence. Small shrubs induced an increase in soil bacterial and fungal biomass, a stimulation of microbial activity and changes in the relative abundance of several bacterial groups, preceding aboveground increase in plant richness and biomass. Shrubs promoted a significant increase of Bacteroidetes, Betaproteobacteria and Gammaproteobacteria abundance in detriment of Actinobacteria and Firmicutes without changes in overall bacterial diversity. Some changes in the microbial community increased with shrub age while other did not, being microbial communities in gaps and under the canopy of large shrubs the most differentiated. We argue that the observed changes in composition and function of soil microbial communities may promote the increase in plant growth and understory species richness along the chronosequence. This emphasizes the importance of plant-soil interactions on defining the structure and composition of both plant and soil microbial communities and their impact on ecosystem functioning.

JAMS REPORT
Ani Penesyan
 
On the last Wednesday of spring we were spoiled with the room on the top floor of the Australian Museum and magnificent views of Sydney, yes, once again! Joining us were not only our regular JAMS crowd, but also visitors from Europe (yes, that is really cold in Europe during this time of the year!)
 

Event Date: 
Wednesday, February 27, 2013 - 18:30 - 19:00
Institution: 
University of Queensland
Title: 

The Big Picture: lessons from a rapidly expanding genomic tree of life.

Abstract: 

Most microorganisms cannot be grown in pure culture (or at least not easily). This has been apparent for decades by comparing the number of cells seen under a microscope to the fraction of those cells that will grow into colony forming units (typically <1%). The advent of culture-independent rRNA-based molecular surveys pioneered by Norman Pace put our degree of ignorance of the microbial world into perspective: dozens of major microbial lineages have emerged over the last 20 years that lack even a single cultured representative. New approaches, such as deep metagenomics and single cell genomics, are now transforming the rRNA-based phylogenetic outlines of the tree of life into a fully fledged genome-based view of the tree. I will present a snapshot overview of the genome tree of the bacterial and archaeal domains and examples of functional insights in the context of a more complete view of microbial evolution.

Event Date: 
Wednesday, February 27, 2013 - 18:00 - 18:30
Institution: 
University of Sydney
Title: 

A tale of two clones; multiple antibiotic resistance in Acinetobacter baumannii .

Abstract: 

The importance of Acinetobacter baumannii in causing nosocomial infections was only recognised in the mid 1980s, making it the least studied of the bacteria that are now resistant to most of the antibiotics that are most important for treatment of such infections. We assembled a large collection of A. baumannii isolates recovered between 1999 and 2011 at hospitals in Sydney, Canberra, Brisbane, Melbourne, Newcastle and Adelaide. All but a few of those that are resistant to multiple antibiotics belong to one of two clonal groups that have recently been found to be globally distributed. Hence, these clones, global clone 1 and 2, have been in Australia at least since the mid 1990s.
Representatives of hospitals and of groups with different carbapenem and aminoglycoside resistance patterns in our collection have been sequenced together with the GC1 and GC2 reference strains from the early 1980s. Trees based on single nucleotide polymorphisms reveal significant diversity in the Australian isolates from one clone and little in the other. Most of the genes conferring resistance to older antibiotics are in the chromosome clustered in one island in GC1 and two in GC2 isolates. However, each of these islands is continually evolving, losing and gaining resistance genes. Further variation arises from the acquisition of different plasmids carrying further resistance genes. Other major but unexpected differences arising within the clones affect the exopolysaccharides. The capsule is an important virulence determinant, and substitution of large chromosomal segments leads to many distinct loci for capsule biosynthesis in each clone.

Event Date: 
Wednesday, November 28, 2012 - 07:00 - 08:00
Institution: 
University of Sydney
Title: 

Biodegradation of dichloroethane by aerobic bacteria at the Botany Industrial Park

Abstract: 

The chlorinated hydrocarbon 1,2-dichloroethane (DCA) is a common pollutant of groundwater, and poses both human and environmental health risks. The Botany Industrial Park in south Sydney is heavily contaminated with DCA and other organochlorines. The main user of the site (Orica Ltd) operates a large groundwater treatment plant (GTP) on site to contain and remediate the DCA-contaminated groundwater. At present, remediation is done by air-stripping and thermal oxidation, but this is very costly and energy-intensive. Orica is interested in alternative technologies for treating the groundwater, including bioremediation. In 2010, a pilot scale membrane bioreactor (MBR) was set up to treat a fraction of the groundwater. The aims of our study were to identify DCA-degrading bacteria and genes in the GTP and on the site at large, define the community structure and ecological successions occurring in the MBR, develop a qPCR for catabolic genes in the DCA biodegradation pathway, and field-test this qPCR assay in the MBR and in a survey of groundwater in monitoring wells on the site. We discovered that DCA-degrading bacteria using a hydrolytic pathway (dhlA/dhlB genes) were widespread and diverse at this site, and that the dhlA gene was carried on a catabolic plasmid. The community in the MBR was dominated by alpha- and beta-proteobacteria, and was highly dynamic, changing dramatically in composition as the percentage of raw groundwater in the feed was increased. By combining dhlA qPCR and 16S pyrosequencing data, we found evidence that thus-far-uncultured species of Azoarcus may play a major role in DCA bioremediation in situ in the MBR.

Event Date: 
Wednesday, November 28, 2012 - 06:15 - 06:30
Institution: 
University of Sydney
Title: 

Does Acinetobacter baumannii have an O antigen?

Abstract: 

 
Acinetobacter baumannii is amongst the most troublesome Gram-negative pathogens worldwide, due to strains that are resistant to multiple antibiotics, disinfection and periods of desiccation. Little is known about the virulence mechanisms, though a role for capsule has been demonstrated. Previous analysis of A. baumannii genome sequences identified a region of extensive diversity presumed to be involved in the synthesis of a surface polysaccharide, variously identified as O-antigen or capsule. We used bioinformatic tools to assess whether this polysaccharide is exported as capsule, or ligated to a lipid A-core oligosaccharide moiety to become the O antigen moiety of lipopolysaccharide. A gene for O-antigen ligase was not found, and we propose that A. baumannii strains produce a capsule (and lipid A-core oligosaccharide), but no lipopolysaccharide.  9 capsule types and 3 core types were found in the 10 completed genomes and more in draft genomes. Multiple capsule types were found in members of the 2 major clonal complexes, and this variation may contribute to the success of the A. baumannii clones by factoring in the evasion of the host immune response.

Syndicate content