Phenotypic Memory and Metabolic Fluctuations

We are studying how bacteria encode and employ memory of past environmental conditions as an adaptation to growth in fluctuating environments.

To study bacterial growth under controlled fluctuating conditions, we developed the chemoflux, a microfluidics device that enables rapid media switching.

This video shows E.coli cells growing in the chemoflux under a periodic environment, with and without glucose, for 4 hours each.

When glucose media is alternated to lactose, cells experience a growth lag during which the lac operon is activated. This behavior is well-known from the work of Jacques Monod in the 1940’s.

We discovered that when cells are grown in a periodically changing environment, lag phases do not occur upon subsequent lactose exposure. Cells use memory of the past lactose exposure to avoid going through additional lags.

This phenotypic memory is due to the stable inheritance of Lac proteins from mother to daughter cells in the absence of the inducer molecule. We showed that bacterial cells can remember environmental states that occurred several generations in the past.

Memory provides a dramatic long-term benefit to bacteria under fluctuating environmental stress, which we are studying in on-going work.