Microbial lag phase should be seen differently as cellular lag phase (cell cycle). Since bacterial lag phase is a community description of the growth and not single cell description there are some differences. Although there are differences in the physiological pattern and expression profile, it is not exactly how you define it as 'repairing and synthesizing biomolecules'. The physiological changes are due to the new environmental induction, availability of nutrient and several different phenomenon. And if we consider the single cell, it is continuously growing/repairing and dividing and a small lag phase. The lag phase of community is comparatively extended due to the few number of cells which are not visible.

I agree with you and Mr Singh

but consider that lag/log/stationary/death phase description according to ratio of growth/death.

In every phase physiological changes happening continuously.

Alireza Mordadi elaborate what you want to say. Of course in different growth phases there are many changes in the physiological and expression profile, and I guess you missed reading that part in the previous post.

Dear Abhijeet

So every cell have their own lag phase as you mentioned about the small lag phase? I somewhat agree with that there is nothing like a real lag phase, it is just due to artefact of the bulk population. A small number of individual cells are metabolically active and exponentially dividing during the lag phase. In the much higher background of inactive cells, the initial increase in cell numbers is too small to be measurable by standard methods producing the impression of a lag phase of the whole culture

Priyanka Mishra Exactly, you got it right. The phenotype heterogeneity in the population (if we see on the single cell level) accounts for the growth rate on the single cell basis. Initially there is a small phase where you can say the cell needs time to deal with the stress due to the method (being used) and new environment, media etc. in short acclimatization. But, one the cell start to divide, there is no such thing like a lag phase. Another thing I would like to point out that, individual cells might have different rate of division and growth due to the phenotypic heterogeneity.

The cell cycle lag phase (commonly refereed to the eukaryotic cells) where the chromosome unwinds and nucleus disappear and all the crossing over event etc. are not comparable to the microbial systems because 1. In microbes, there is no nuclear apparatus and no pattern like mitosis/meiosis. 2. In microbes the lag phase is used to define the growth of a whole population. And you are absolutely correct with the statement - " initial increase in cell numbers is too small to be measurable by standard methods producing the impression of a lag phase of the whole culture."

Abhijeet Singh Then, what do you think when cells decide to divide? I mean, they reach certain cell size than they want to divide or there is any signalling molecule governing cell division in microbes.

Priyanka Mishra This is a question which is not directly related to the microbial lag phase and it is more towards the individual cell growth. There are some studies which were focused on the what happens to the cell during growth, how the cells grow (cell wall loosening and integration of the new molecular threads in the existing molecular mesh of the cell envelop), identification/cellular determination of the mother pole. And yes, there are some deterministic molecular governs the cell size and act as a trigger for the cell division.

Priyanka Mishra

I suggest you to study quorum sensing of bacteria

One thing to consider when talking about the lag phase of bacteria is that different bacteria respond differently to their surroundings and some bacteria (notably Enterococcus faecalis) do not go into a typical lag phase). Individual cells might show a lag, while the composite shows no lag.

Lag phase is the period of adaptation of bacterial cells to the new environment and in which no bacterial multiplication and it is affected by several factors like size of inoculum, age of inoculum, Previous adaptation on the medium, nutritive material in the medium and species of bacteria

Priyanka Mishra : concerning bacterial division regulation please have a look at the following link:

https://news.harvard.edu/gazette/story/2014/07/sizing-up-bacteria/

Best regards

Vit

Vit Mateju Thanks for the link

Jay Sperry I am bit skeptic about "Individual cells might show a lag, while the composite shows no lag." Should we call the abnormal growth of certain bacteria as lag if the composite is not showing any lag?

Abhijeet, you might consider that our normal conditions for growing bacteria in the laboratory is in many senses artificial. Look to what has been learned about the growth of bacteria as biofilms, where there are groups of bacteria in different physiological phases of growth (metabolism).

Vit Mateju

Some of questions in this way are answered with study of quorum sensing. Am I right?

Alireza Mordadi:

You are right.

REgards

Vit

That is right, therefore, the size of bacterial cell increase in this lag phase I.e. there is bacterial growth but no bacterial multiplication

Chronologically-

1) Alireza Mordadi - No quorum sensing is neither a signaling mechanism nor it regulates the deterministic factor for cells size determination or trigger for cell division. It is the mechanism which overall related with the population density in a particular environment. Basically it is radar homolog in bacteria. It might indirectly involve in the aforementioned, but not directly. Therefore, recommending quorum sensing (a wider topic) for a specific question is not supported.

2) Jay Sperry - since the discussion was not related to the biofilm but a bacterial growth in normal growth protocols, so I tried to relate the your previous comment to the context. And again it does not fit well, as you mentioned only one bacteria without mentioning any biofilm formation. "E. Faecalis forms biofilm after 14-15 days of incubation"(PMID: 27095620). So, what happens meanwhile, do cells divide or they remain in lag phase? And if we talk about E. faecalis biofilms, "SEM showed E. faecalis growth at all times" (PMID: 27095620).

Nevertheless, biofilms are special microbial structures, where the conventional growth curve does not applies. Therefore, involving biofilms in this discussion is like comparing apples and pears.

* I agree with your comment that bacteria might have different physiological growth phases, and it has been considered previously in the discussion above. Each species has its own growth rate and ofcourse cells requires time, a certain cell size and mass to initiate the division. But should we call it lag phase?

Abhijeet, (1) signaling involves signals, and signals are signs, and signs are sensed; hence, quorum sensing is a signaling mechanism; (2) population density is a number of individuals per unit of volume, which is the basis for determining the change of the number of individuals per unit of volume per unit of time, from which the growth can be determined both quantitatively (rate) and qualitatively (stage).

Martin Klvana Thankyou for the grammatical lesson, but grammar also involves punctuation, so I kindly request you to please re-read the sentence till the full stop. I understand your enthusiasm and appreciate your knowledge but please reconsider what you wrote in the previous context.

Again, thanks for clearing the basics of physics and letting me know what density is. But I don't have any idea what point you wanted to make here ?

[just a small comment of your first point -

signal basically refers to the transmitter and sensing refers to the receiver end. The signal molecules are continuously produced but it is only sensed when the concentration of that signal molecule reaches the threshold and that triggers further metabolic cascade. Therefore the mechanism is called quorum sensing and not signalling, because it is based on sensing and not signalling]

Abhijeet, (1) i see, double negative means positive, so what you mean is "quorum sensing is a signaling mechanism and it regulates the deterministic factor for cells size determination and trigger for cell division"?; (2) if my current interpretation is correct, don't you contradict yourself if you say that quorum sensing is not relevant to the discussion about "microbial lag phase"?; (3) signaling and sensing are two sides of the same coin: the bacterium signals, "I am here!" and senses "I see you"--quorum sensing could equally well be called quorum signalling (a dispute about these two expressions is a pure logomachy), or quorum signaling-and-sensing, because it is as much about signaling (the amount of which depends on the population density) as it is about sensing (which interprets the population density); (4) how do you determine the reproduction rate and stage (e.g., lag phase, exponential phase, stationary phase) if not by counting the number of living bacteria per unit of volume?; (5) the number of living bacteria per unit of volume is population density--isn't population density that which is signaled and sensed by quorum signaling-and-sensing mechanism? If yes, why then do you find quorum sensing irrelevant to the discussion about "microbial lag phase"?

Freshly inoculated cultures take some time to build up metabolically produced CO2, which is needed for carboxylation reactions like that catalyze by acetyl-CoA carboxylase. Lag phase is prevented if the medium is sparged with CO2 before inoculation. These results from old work, with Rhizobium, I think. @

Martin Klvana

Thanks for your very clear explanation of quorum sensing

If yes, why then do you find quorum sensing irrelevant to the discussion about "microbial lag phase"?

Martin Klvana - Exactly, this is the fault in the communication. The later half of the discussion was not about microbial lag phase, Priyanka Mishra asked about the "trigger for cell division" ( what do you think when cells decide to divide ?). Answering this question with quorum sensing is like-

person 1 (question) - where do you live ?

person 2 (answer) - on earth !

I am not saying there is no quorum sensing, ofcourse it is an important part of the growing bacterial colony, but answer only quorum sensing for all question without any explanation, do you think its logical? Okay, give me one example where you can say quorum sensing molecule directly trigger any specific event without any further metabolic cascade.

Moreover, there are differences in quorum sensing in gram positive and gram negative. Still do you say quorum sensing molecule from all bacteria irrespective of the origin work in a same/similar fashion?

Abhijeet, a signaling/sensing cascade should be more properly called a network. Everything is interconnected. Just because A communicates with C via B, rather than directly, does not mean that A does not trigger any specific event. From the perspective of A, B is not only a middleman between A and C but also a direct partner. And for B, both A and C are direct partners. What is direct and indirect depends on the reference point.

Lag phase is the period between the introduction of a microorganism into a culture medium and the time it begins to increase exponentially. During the lag phase:

1. Cell number remains relatively constant prior to rapid growth.

2. The bacteria adapt themselves to growth conditions, the individual bacteria are maturing and not yet able to divide.

3. The cells are metabolically active and increase only in cell size.

4. They are also synthesizing the enzymes, RNA, and cellular components and factors necessary for growth and needed for cell division and population growth under their new environmental conditions. The population then enters the log phase, in which cell numbers increase in a logarithmic fashion.

5. Cells change very little because the cells do not immediately reproduce in a new medium. Therefore, lag phase could include the repair of macromolecular damage that accumulated during stationary phase.

Dear Dr., Mina Karimi Avargani

you mentioned the following point

4. They are also synthesizing the enzymes, RNA, and cellular components and factors necessary for growth and needed for cell division and population growth under their new environmental conditions. The population then enters the log phase, in which cell numbers increase in a logarithmic fashion.

could you please send me the reference whether paper article or review or book chapter which support that the bacterial cell have ability to synthesis enzymes in lag phase