Pseudo live-twtting of Richard Losick’s keynote lecture @EMBOmtg.
Disclaimer (for EMBO organizers): I will only reproduce results that have been published in the two following papers (check the abstracts)
Chai Y, Norman T, Kolter R, Losick R.
Genes Dev. 2010 Apr 15;24(8):754-65. Epub 2010 Mar 29.
Kolodkin-Gal I, Romero D, Cao S, Clardy J, Kolter R, Losick R.
Science. 2010 Apr 30;328(5978):627-9.
Title : Life and Death of a bacterial community
Communities of bacteria are everywhere : holes in ships, dental cavities, etc… They form biofilms. (French speaking readers can have a look at this bacterioblog’s post on biofilms).
B. Subtilis naturally form robust biofilms on the roots of plants, nice picture of Losick with Chinese farmers (well, farmer officials at least).
Cells in the biofilm display sophiticated organization : in parallel chains held together by extra cellular matrix.
We start with description of the Genes Dev paper results.
Matrix production : 3 proteins implicated named SinR, Slr and SinI (see attached figure from reference given above)
SinR repressor of matrix genes, and of gene Slr
Slr inhibits SinR
SinI triggers biofilm formation
Slr and SinR mutually antagonistic : SinR represses transcription for Slr, Slr titrates SinR (post-transcriptional repression)
Chaining of cells ? involves autolysin gene. autolysin on : individual cell, off : chains of cells form
The Slr-SinR Complex represses autolysin genes.
The loop exists in Slr Low and Slr High states . These are long lived states for the cells (bistability). Change of stable states is triggered by SinI protein. Yet another example of so-called « Epigenetic switch »
Losick has just pronounced the words « hysteresis » and « bistability ». Music to my ears #EMBOmtg
Losick gave further insights on how you switch back to the low Slr state. This seems unpublished, I consider it confidential.
We know switch to the description of the Science paper results.
Actually, cells in the aging biofilm escape from the matrix. How do they do that ?
Idea : there might be a protein released by bacteria dissolving the biofilm. Experiment : take medium from a 8 day old colony, puts it back in a young culture-> biofilm is actually removed from the young colony. This proves existence of a dissolving factor.
This factor is a mix of 4 amino-acids. D-amino acids are breaking the matrix.
Cells in the biofilm are held togetehre by amyloid fibers; D-amino acids trigger the release of the fibers.
D-amino acid are derived from L-amino acid by enzymes called racemases. Overproduction of racemase gene blocks biofilm formation. racX is transcribed at late times.
Losick gave further insights on racX regulations, this seems to be unpublished -> I consider it confidential.
Incorporation of D-amino acids might be a general mechanism. Seems to work for S. Aureus and Pseudomonas at least.
Twitter conclusion by Rafael_RNAm
I know some « D-amino people »: when they arrive at a group, it disassemble. #embomtg