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Sleator Lab Identifies Single Point Mutation in Listeria Monocytogenes

23 March 2013

The bacterial foodborne pathogen, Listeria monocytogenes is the causative agent of listeriosis—a debilitating disease linked with about 2,500 illnesses and more than 500 deaths per annum in the US alone.

A characteristic feature of L. monocytogenes is its ability to grow at refrigeration temperatures and in the presence of high concentrations of salt—traditional food preservation techniques, which arrest the growth of most other pathogens.

Work in the Sleator lab has shown that the bacterium protects itself from such stresses by twisting into a protective corkscrew type shape in an effort to reduce its exposure to the stress—in the same way a human might wrap up tight—hugging the core to reduce the effects of the cold.

Furthermore, Sleator and colleagues have identified a single point mutation (out of a total of 3 million or so nucleotides that constitute the entire listerial genome), which dramatically improves the growth of the pathogen in the refrigerator.

The research paper, "A single point mutation in the listerial betL sA-dependent promoter leads to improved osmo- and chill-tolerance and a morphological shift at elevated osmolarity," will be published in the November/December 2013 issue of Bioengineered.

The research team of Roland F. Hoffmann, Susan McLernon, Audrey Feeney, Colin Hill and Roy D. Sleator said that Betaine uptake in Listeria monocytogenes is mediated by three independent transport systems, the simplest of which in genetic terms is the secondary transporter BetL.

Using a random mutagenesis approach, based on the E. coli XL1 Red mutator strain, the researchers identified a single point mutation in a putative promoter region upstream of the BetL coding region, which leads to a significant increase in betL transcript levels under osmo- and chill-stress conditions and a concomitant increase in stress tolerance.

The mutation appears to counter the heretofore unreported “twisted” cell morphology observed for L. monocytogenes grown at elevated osmolarities in tryptone soy broth, the study says.

Sleator claims that this mutation represents "a double edged sword;" "from a food safety perspective, a single point mutation with the potential to induce such dramatic shifts in cell growth and survival at low temperatures—making an already dangerous pathogen even more formidable—raises significant food-safety concerns which need to be addressed."

However, from a synthetic biology point of view, such a boosted-stress resistance gene represents a useful BioBrick (or building block) for the design of more physiologically robust probiotics or, indeed, plants that are more resistant to cold arid conditions.

March 2013

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