800px-Corynebacteriumdiphtheriae copacopacThis week’s #microtwjc coincides with the Society for General Microbiology’s (SGM’s) Autumn Conference.  Sadly I can’t be there this time but I know many #microtwjc regulars are going so I shall be following the conference hashtag, #sgmsus, avidly.

The paper that we will be looking at this week is published in one of the SGM journals: in this journal club we only look at papers that everyone can access and so the SGM has very kindly made it free for everyone to access until 3rd September – thanks very much SGM!

Before I get onto the paper – if this is your first time learning about #microtwjc , welcome 🙂 !  We’re a very friendly bunch who enjoy getting together to discuss papers and we’d love you to join us (no experience necessary!).  All you have to do is follow the hashtag #microtwjc from 8pm on Tues.  You can do this simply using the search function on Twitter or you can use something like Tweetdeck or Twitterfall.  If you’re new to Twitter then this LSE guide is great for getting your head around it.

Lurking silently is fine but we’d love people to contribute as well (even if it’s just to say “I didn’t really understand this bit…” – you won’t be the only one I promise!  We’re a group with a wide range of experiences and so at least one of us will be unfamiliar with the topic being discussed.)  If you do want to ask questions/make points etc. don’t forget to add the hashtag #microtwjc somewhere in your tweet so we all see it.

So on to this week’s paper:

Vartul Sangal, Peter C. Fineran and Paul A. Hoskisson  (2013).  Novel configurations of Type I and II CRISPR-Cas systems in Corynebacterium diphtheria

(It’s so hot off the press that it’s still in the prepublished pdf version!)

Abstract:

Clustered regularly interspaced short palindromic repeats (CRISPRs) are major barriers to recombination through recognition of invading nucleic acids, such as phage and plasmids, and promoting their degredation through the action of CRISPR associated (Cas) proteins. The genomic comparison of 17 Corynebacterium diphtheriae strains led to the identification of three novel CRISPR-Cas system variants, based on the Type II (Type II-C) or Type I-E systems. The Type II-C system was the most common (11/17 isolates) but it lacked the csn2 or cas4 genes that are involved in spacer acquisition. We also identified this variant Type II-C CRISPR-Cas system is also present in other bacteria, and the first system was recently characterised in Neiserria meningitidis. In the remaining isolates, the Type II-C system was replaced by a variant of Type I-E (I-E-a), where the repeat arrays are inserted between the cas3 and cse1 genes. Three isolates with the Type II-C system also possess an additional variant of Type I-E (I-E-b), elsewhere in the genome, that exhibits a novel divergent gene organization within the cas operon. The nucleotide sequences of the palindromic repeats and the cas1 gene were phylogenetically incongruent to the core genome. The G+C content of the systems is lower (46.0-49.5%) than the overall G+C content (53%), and they are flanked by mobile genetic elements, providing evidence they were acquired in three independent horizontal gene transfer events. The majority of spacers lack identity with known phage or plasmid sequences, indicating that there is an unexplored reservoir of corynebacteriophages and plasmids. These novel CRISPR-Cas systems may represent a unique mechanism for spacer acquisions and defence against invading DNA.

Discussion points:

  1. What did you think of the paper? Was it easy to read? Did the results back up the conclusions drawn? etc.
  2. What do the results mean in the broader context of research on C. diphtheriae?
  3. What work would you like to see done next?
  4. On a broader note, where do you see CRISPR work in general heading?

As usual, if you do write a blog post about the paper please plug it below in the comments – it’s always very helpful when people do this.

I look forward to tweeting old and new members alike on Tues 3rd September, 8pm UK time.

If you want email reminders about the journal club (no emails about anything else I promise) – please contact me: zoonotica at hotmail dot co dot uk.

Image: Published under a Creative Commons 3.0 licence by Copacopac

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