What do you mean by "after addition of depleted source" ?

As Utsa mentionned, bacteria stop dividing when nutrients are lacking OR when waste accumulates. The minute they come back to optimal growth conditions, they will start dividing again to ultimately reach log-phase.

One way to do this is to take an aliquot of your stationnary-phase culture and transfer it to fresh media. It will get back to log-phase within a few hours.

What do you mean by "after addition of depleted source" ?

As Utsa mentionned, bacteria stop dividing when nutrients are lacking OR when waste accumulates. The minute they come back to optimal growth conditions, they will start dividing again to ultimately reach log-phase.

One way to do this is to take an aliquot of your stationnary-phase culture and transfer it to fresh media. It will get back to log-phase within a few hours.

Thanks Martin Chenal and Utsa Roy

Maybe first to clarfiy: we are experimenting with a new kind of minimal medium.

With "depletion of source", I mean that we had a strong feeling that the culture ran out of nitrogen source. Depletion of glucose was recently tested using a glucose assay which showed that still high amounts of glucose were present.

We added "extra" buffered nitrogen source and, indeed, we saw the OD again started to go up exponentially. However, I expected it to have the same "amount/duration" of log-phase with the same amount of increase in OD as seen during/after the initial log-phase before depletion. Unfortunately, this was not the case. This extra log-phase had a significantly lower maximum slope and shorter duration before reaching the stationary phase.

We are now convinced that, also according to the answers of Martin and Utsa,

- or the pH dropped because of metabolite accumulation.

- or there was too little volume left to be able to accomodate a higher biomass.

Or do you maybe have a different reason for why the OD only slightly, but again exponentially, increased ?

Dear Utsa . ..... if you take bacteria in a stationary phase and cultured it in patched culture, bacteria maybe back to log phase because you have (live cells=dead cells) so, live cells can make a new growth curve again

Thank you Miaad K. Alkhudhairy

Yes, so this is the theory some of my colleagues disagree with. In theory, if you find a way to accomodate for metabolic burden and necessary volume expansion (aka. minimize amount of dead cells), the OD could in fact increase unlimitedly.

In practice, ba. can back to log phase because sometimes we neglect the preservation bacterial samples and recultured them again, so we find it regenerate and give abundant production even though the bacteria went via bad conditions (food shortage , toxic accumulation .... etc).

All the proposed reasons seem easy to test (pH change, amount of nitrogen). Why would there be many dead cells in the culture (they don't have telomeres)? The spent medium can be analyzed to look for any metabolites that would affect the growth rate. What source of nitrogen did you add? Was it pure? In yeast cells it is known that elements like Zinc can have a similar effect. Maybe the nitrogen source was the sole reason to restart the logarithmic growth, or maybe it contained traces of key elements that had been depleted in the original culture.

Thanks, Tracy, we all know that in any culture cells die (yeast, bacteria, any culture). My comment is about how many. Too many dead cells would not be normal in a culture that just entered stationary phase.