Twim #7

Anouther very informative episode of twiM. There were two main points, the extracellular death factor in E.coli and the protein turnover in cyanobacteria allowing them to be photosynthetic during the day and nitrogen fixing at night, mostly focusing on iron recycling. This post will focuse on EDF

Extracellular death factor is a qourum sensing molecule that interacts with toxin anti toxin system in E.coli, amplifying the activity of two toxins called MazF and ChpBK. The theories behind this are a bit strange, group theoryie and I haven’t comprehended them yet. If it is related to cannabilism and bacteria programmed cell death, bacteria eating their brethren, maybe it could be tied in competence as both might be nutritional in nature, if you’re going to be cannabalistic you might as well be competent. There is an interesting paper that links it with peptidoglycan synthesis! A grad student I know in the neighboring tuberculus lab is working with toxin-antitoxin systems and I’ve learned a bit about it from him.

The really interesting thing that I got from this is that extra cellular death factor is a pentapeptide that acts as a qourum sensing molecule,  H-Asn-Asn-Trp-Asn-Asn-OH (NNWNN). Haemophilus influeenzae doesn’t have qourum sensing -I’m not sure how we know this, assuming someone tested that supernatant from late log cells doesn’t induce competence, atleast not in wildtype. However one of the theories we have about murE is that the mutations alter the proteins specifity from adding meso-DAP to adding LL-DAP creating an alterted pentapeptide. The normal Meso-MurNAC pentapeptide is found in high levels in late log and interacts with the ampR homolog to cause it to act as a repressor. An undergrad worked on this idea but nothing was ever concluded, although there should be good avenues to experiment – knocking out the gene dapF dramastically increases LL-DAP levels, from a 1:1 ratio to 5000:1(In E.coli. Some bacteria have an alternative pathway to creating meso-DAP and it’s not clear if HI does)

There’s a good post about L-forms on small things considered.

1 Comment (+add yours?)

  1. Rosie Redfield
    May 24, 2011 @ 07:37:07

    Another adaptationist just-so story…


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