Integron

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.

Event Date: 
Wednesday, August 28, 2013 - 19:00 - 20:00
Institution: 
iThree Institute UTS
Title: 

Genome plasticity in Vibrio species – how lateral gene transfer directs niche specialisation and pathogenicity

Abstract: 

Bacteria of the Vibrio genus are abundant in aquatic environments, fulfil important nutrient cycling roles and are often found in association with marine animals such as corals, molluscs, sponges, crustaceans and fish. This diversity in niche occupation is a feature of Vibrio species and is largely (or at least in significant part) driven by lateral gene transfer (LGT). LGT is a two-step process firstly requiring physical transfer of DNA from one bacterial cell to another followed by subsequent integration of the transferred DNA into the genome thus allowing stable inheritance and expression. Numerous mechanisms for integration exist such as homologous recombination and a wide-range of diverse genetic elements such as transposons, integrative conjugative elements, prophages and integrons. Using two Vibrios species, V. rotiferianus and V. cholerae, research in our laboratory has sought to understand how mobile DNA contributes to vibrio evolution, niche specialisation and pathogenicity. In V. rotiferianus, we have been researching the integron, a genetic element that contributes up to 3% of a vibrios genome in laterally acquired mobile DNA. This region is dynamic and evolves at a faster rate than mutation. Our research has shown that this region provides the organism a mechanism for reworking surface polysaccharide affecting biofilm formation and potentially interactions with higher organisms. Furthermore, we have been researching evolution in V. cholerae isolated from Sydney estuarine waters. These isolates are pathogenic in animal models with all lacking the usual virulence factors of cholera toxin and colonisation factor tcpA and most lacking type III secretion indicating the presence of novel virulence factors. One isolate we are focussing on contains a novel 32-kb mobile element inserted into the indigenous recA but carries a unique recA with only 80% identity to other V. cholerae recA genes. Overall, our research demonstrates the plasticity of vibrio genomes and the significant contribution that LGT makes to the continuing evolution to the Vibrio genus.

JAMS celebrated July at the Australian Museum with a diverse series of talks and food and drinks, kindly supported by ASM.

Rita Rapa (UTS) started us off describing the integron/gene cassette system in the Vibrio genus. These gene cassettes add to the adaptive potential of Vibrio and are likely to be an important driver in the evolution of Vibrio in their respective niches. Through whole cell proteomic analysis, deletions in the gene cassette array exhibit altered surface associated structures. Her future work will focus on how these deletions impact Vibrio physiology.
Event Date: 
Wednesday, July 27, 2011 - 18:00 - 18:15
Institution: 
UTS
Title: 

Gene Cassette Products and Their Role in Vibrio Physiology: A Proteomics Approach

Abstract: 

Vibrios are marine bacteria that are highly adaptable and subsequently capable of colonizing various niches. The integron/gene cassette system is a genetic element present in Vibrio spp., that incorporates mobile genes termed gene cassettes into a reserved genetic site via site-specific recombination. The integron consists of three basic elements: an integrase gene (IntI), an attachment site (attI) and a promoter (Pc). Gene cassettes contain an open reading frame and an IntI-identifiable recombination site called attC. Insertion (and excision) of gene cassettes is facilitated by an integrase-mediated recombination between attI and attC where cassettes can be accumulated forming a cassette array. Cassette arrays in Vibrio spp. are uniquely large, containing hundreds of contiguous gene cassettes. There is a consensus that these gene cassettes add to the adaptive potential of vibrios and have likely been an important driver in the evolution of vibrios into their respective niches. How this is achieved has been difficult to understand since 80% of gene cassettes are novel and consequently of unknown physiological function. Whole cell proteomic analysis comparing wild-type Vibrio rotiferianus DAT722 with isogenic mutants that have deletions in regions of their gene cassette array show the deletions have altered surface associated structures including extracellular polysaccharide and outer membrane proteins/porins. Studies into how the deletions impact the secretome/surfaceome are currently underway. This data aims to understand how the integron/gene cassette system drives Vibrio evolution by determining how these unique genes impact vibrio physiology.

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