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This week’s paper reports on the characterisation of a gene, pgp1, that is important for the helical shape of the bacterium Campylobacter jejuni.

The authors first identified the gene by screening for hypofluorescent C. jejuni mutants  with calcofluor white (which reacts with certain carbohydrate linkages and fluoresces under UV light).  (The researchers in previous work had shown that hypofluorescent mutants “exhibit changes in pathogenesis, virulence, fundamental and/or stress survival phenotypes”).  They then investigated the functional consequences of loss of this gene for C. jejuni by creating a non-polar pgp1 targeted deletion strain .

Having identified that the pgp1 gene is required for the helical shape of C. jejuni and having identified that it plays a role in motility and biofilm formation they went on to characterise the muropeptide content of the C. jejuni strain and determine how this is altered by loss of pgp1 function.

Then they looked at the effect the pgp1 gene had on how C. jejuni interacts with host cells, finding that the deletion strain showed a decreased ability to colonise one day old chicks but that in vitro there was little difference between the deletion strain and the wild type strain when it came to invasion and intracellular survival in epithelial and macrophage cell line.  Finally, they showed that the deletion strain did produce an increased epithelial cell Nod1  response compared to the wild type and increased IL-8 production by epithelial cells.

In the discussion the authors state that “identification and characterisation of pgp1 provides a critical first step in understanding how shape and PG modifications impact C. jejuni pathogenesis“.  They conclude by saying that the deletion strain “will be a valuable tool to continue to study the effects of the loss of C. jejuni helical shape on its biology and pathogenesis“.

Discussion points

These are points/questions that occurred to me as I read the paper.  If you have anything else you think would be interesting to discuss please post in the comments below.

  • Was the paper written clearly and logically with the results informing the discussion?
  • Much of this paper is by necessity descriptive, as the authors discuss how they characterised the gene.  Once they identified its role in C. jejuni biology was there a clear hypothesis for its role in C. jejuni pathogenesis?
  • Have the authors shown sufficiently that it is pgp1‘s role in helical shape formation that is directly affecting C. jejuni‘s pathogenesis?
  • Are there any other experiments you would like to have seen done?

Hello and welcome to the website for the Twitter Microbiology Journal Club #microtwjc !

Having seen the success of #twitjc and #phtwitjc I decided to try setting a microbiology one up.

Luckily I’ve had a lot of offers of help and you’ll be meeting the #microtwjc team as the sessions go on (although if you also want to get involved it’s not too late – just tweet me (@_zoonotica_) or comment below.)

The journal club will take place on alternate Tuesdays at 8pm British Summer Time and we aim to cover topics across the whole spectrum of ‘microbiology’.

The first paper (for the session on 8th May) is my choice and is:

Peptidoglycan-Modifying Enzyme Pgp1 Is Required for Helical Cell Shape and Pathogenicity Traits in Campylobacter jejuni 

(Full reference: Frirdich E, Biboy J, Adams C, Lee J, Ellermeier J, et al. (2012) Peptidoglycan-Modifying Enzyme Pgp1 Is Required for Helical Cell Shape and Pathogenicity Traits in Campylobacter jejuniPLoS Pathog 8(3): e1002602. doi:10.1371/journal.ppat.1002602 )

I will post a list of discussion points later on this week (if you have any points please do comment below) but for now here is the Author Summary:

Bacterial cell shape is dictated by the composition of the cell envelope component peptidoglycan. Some important pathogens have a characteristic helical corkscrew morphology that may help them burrow into mucus overlaying cells to initiate colonization and pathogenicity.  One example is Campylobacter jejuni, the leading cause of bacterial-induced diarrheal disease in the developed world. Direct evidence supporting the hypothesis that C. jejuni shape is related to its pathogenicity traits has not previously been provided.

We identified a gene encoding a peptidase modifying peptidoglycan that is essential for maintaining the C. jejuni corkscrew shape. We can now connect a C. jejuni gene with morphology and peptidoglycan biosynthesis. Loss of this gene was also found to affect pathogenic attributes such as chicken colonization, biofilms, motility, and activation of host inflammatory mediators.

In addition, this is the first study to thoroughly characterize C. jejuni peptidoglycan structure and to identify a gene involved in peptidoglycan maintenance. Our findings highlight an emerging theme in bacterial pathogenesis research: the connection between bacterial cell biology and pathogenesis. Finally, our characterization of C. jejuni cell shape and peptidoglycan provides a starting point for further work in this area in C. jejuni and other bacteria with curved and helical morphologies.”

The hashtag for next Tuesday and for every week is #microtwjc  If you’re not sure how best to follow the conversation next Tuesday – I’m going to be trialing TweetChat which should allow me to follow the hashtag and nothing else more easily…

If this whole thing including Twitter is new to you (as I know it is to some) the LSE has produced a guide for academics: “Using Twitter in university research, teaching and impact activities” (links to a PDF) which is a great starting point.

I’m so excited and can’t wait to see you all 8pm BST next Tues 8th May  😀