Euprymna scolopes

Euprymna scolopes

Next Tuesday marks the 1 year anniversary of #microtwjc – I can’t believe it’s come around so quickly!  Thank you to everyone who has been involved running the sessions, taking part in them and advertising them to colleagues.  Please continue!  It wouldn’t be half as much fun without you all 🙂

On to this week’s paper

This week I’ve chosen this paper in mBio by Heath-Heckman et al, because I am constantly amazed at the number of different ways the microbes that live in or on us affect us, our bodies and our behaviours (although I will admit to also being drawn to cute animals like the one above!)

Bacterial Bioluminescence Regulates Expression of a Host Cryptochrome Gene in the Squid-Vibrio Symbiosis

Elizabeth A. C. Heath-Heckman, Suzanne M. Peyer, Cheryl A. Whistler,Michael A. Apicella, William E. Goldman, Margaret J. McFall-Ngai


In mammals, biological rhythms of the intestinal epithelium and the associated mucosal immune system regulate such diverse processes as lipid trafficking and the immune response to pathogens. While these same processes are affected by the diverse resident microbiota, the extent to which these microbial communities control or are controlled by these rhythms has not been addressed. This study provides evidence that the presentation of three bacterial products (lipid A, peptidoglycan monomer, and blue light) is required for cyclic expression of a cryptochrome gene in the symbiotic organ. The finding that bacteria can directly influence the transcription of a gene encoding a protein implicated in the entrainment of circadian rhythms provides the first evidence for the role of bacterial symbionts in influencing, and perhaps driving, peripheral circadian oscillators in the host.


The symbiosis between the squid Euprymna scolopes and its luminous symbiont, Vibrio fischeri, is characterized by daily transcriptional rhythms in both partners and daily fluctuations in symbiont luminescence. In this study, we sought to determine whether symbionts affect host transcriptional rhythms. We identified two transcripts in host tissues (E. scolopes cry1 [escry1] and escry2) that encode cryptochromes, proteins that influence circadian rhythms in other systems. Both genes cycled daily in the head of the squid, with a pattern similar to that of other animals, in which expression of certain cry genes is entrained by environmental light. In contrast, escry1 expression cycled in the symbiont-colonized light organ with 8-fold upregulation coincident with the rhythms of bacterial luminescence, which are offset from the day/night light regime. Colonization of the juvenile light organ by symbionts was required for induction of escry1 cycling. Further, analysis with a mutant strain defective in light production showed that symbiont luminescence is essential for cycling of escry1; this defect could be complemented by presentation of exogenous blue light. However, blue-light exposure alone did not induce cycling in nonsymbiotic animals, but addition of molecules of the symbiont cell envelope to light-exposed animals did recover significant cycling activity, showing that light acts in synergy with other symbiont features to induce cycling. While symbiont luminescence may be a character specific to rhythms of the squid-vibrio association, resident microbial partners could similarly influence well-documented daily rhythms in other systems, such as the mammalian gut.

There is a blogpost on this article available at mBiosphere.  If anyone else writes/has written a post on the article please don’t be shy about posting the link below.

Questions to think about this week…

  1. Was the paper well written?
  2. Were the methods sound?
  3. Were there any other experiments you would like to see in there?
  4. What do the results mean in a broader context?
  5. What other influences do we know that commensal flora have on their hosts?

Please spread the word about Tuesday’s session – it would be great for the birthday edition to be busy 🙂

See you there

Image: Licenced under Creative Commons Attribution-Share Alike 3.0 Unported license by Nick Hobgood