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In my lab we've observed a phenomenon in which a culture of E. coli is found to shift from normal rod growth to filamentous growth and then back to normal rod growth again several times over the course of 400 hours. This was shown by an OD600 graph which oscillates from high values (~5) to low (~0.5) (the culture was also viewed directly).

The shift to filamentous growth is usually associated with an SOS response in E. coli and this makes sense (the media is M9 supplemented with 0.2% casamino acid and 0.1mM thiamine hydrochloride), however we don't know why it switches back from filamentous to normal growth.

Has anyone observed a similar phenomenon? Does anyone have any suggestions why this might be happening?

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How exactly is the culture maintained over the 400 h period? Are there any periodic events? –  Alan Boyd Jun 27 '13 at 17:07
I have found that E.coli turns from single cells to filaments when stress by predators such as myxobacteria or amoeba. why in the same batch cells turn from filaments to single cells is not clear to me. Is it a fed bactch and do they keep growing? –  user5086 Dec 4 '13 at 11:46
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2 Answers 2

Expression of sfiA (sulA) causes filamentation during the SOS response, so presumably sfiA is induced, as part of SOS, in response to some sort of DNA damage. Once the DNA damage is repaired the SOS genes, including sfiA, will be repressed again and normal growth will resume.

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In addition to the other answer(s), E. coli has been shown to have filamentous spikes even under controlled conditions. This is not the same situation as it sounds like you have a non synchronized culture in which this happens, but it could be related.

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