[BryanC]

In an oxygen-absent environment, lactic acid fermentation occurs. Pyruvate is broken down to oxidise NADH to NAD+. NAD+ can then be used in glycolysis pathway. The final product of fermentation = 2 NAD+

However, glycolysis also requires an investment of 2 ATP. The question is, since ATP is never produced during fermentation, where would the initial investment of 2 ATP come from in an oxygen-absent environment?

If initial investment of 2 ATP comes from the environment that the cell is already in, does this mean that a cell in an oxygen-depleted environment will die once this initial ATP is used up?
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[Babcock_Hall]

Some bacteria are able to survive in both an anaerobic and an aerobic environment (called facultative anaerobes IIRC).  Therefore, I think that the answer to your question is no.  Think about the Pasteur effect.

The question may be using the word fermentation differently from how I typically use it.  If the question defines fermentation as the process of converting pyruvate and NADH into lactate and NAD, then we can move forward (if the question defines fermentation as the conversion of glucose all the way to lactate, then I am less certain of what to do).  Do you know the balanced equation for glycolysis?

[Babcock_Hall]

Some textbooks divide glycolysis into a preparatory phase and a payoff phase.  If your book does, then see if you can work with that.

[BryanC]

Some bacteria are able to survive in both an anaerobic and an aerobic environment (called facultative anaerobes IIRC).  Therefore, I think that the answer to your question is no.  Think about the Pasteur effect.

The question may be using the word fermentation differently from how I typically use it.  If the question defines fermentation as the process of converting pyruvate and NADH into lactate and NAD, then we can move forward (if the question defines fermentation as the conversion of glucose all the way to lactate, then I am less certain of what to do).  Do you know the balanced equation for glycolysis?

I would be referring to fermentation as the process of converting pyruvate and NADH to lactate and NAD+.

Yes I am aware of it. It is:
Glucose + 2NAD⁺ + 2 ADP + 2P -> 2 Pyruvate + 2 H₂O + 2 NADH + 2 ATP + 2 H⁺

But at the beginning of glycolysis 2 ATP is required for the phosphorylation of glucose to glucose 6P and fructose 6P to fructose 1,6 BP. How would these 2 ATP be produced in a bacteria that does not naturally produce the enzymes to utilise Kreb's cycle as a metabolic pathway?

[Arkcon]

https://en.wikipedia.org/wiki/Adenosine_triphosphate#Production_from_AMP_and_ADP

ATP isn't produced in great amounts by the Kreb's cycle.  That particular pathway produces one per cycle, that is two per acetate that feeds in, if I recall correctly, and I may not be.

Much ATP is produced by oxidation of NADH (and others) by the electron transport chain, if the organism does that.

In practical terms, ATP id produced by the ATPsynthase trans-membrane protein, which uses a proton gradient to drive it, and those protons can come from anywhere:  https://en.wikipedia.org/wiki/ATP_synthase

But the original Wikipedia link I posted above gives a variety of sources.

[Babcock_Hall]

BryanC,

A typical mammalian cell is regulated in such a way that most of the adenine nucleotides (AMP, ADP, ATP) are in the form of ATP; in other words quantity known as the energy charge is high (IIRC the EC is about 0.9).  I strongly suspect that microorganisms are not too dissimilar.  In other words the cells are constantly performing catabolic reactions and regulating the speed of the anabolic reactions so as to maintain a high concentration of ATP.  So if a cell spends a little ATP in the  preparatory phase of glycolysis, it is not a big deal.  The payoff reactions that produce ATP will happen quickly to replenish it.  I would have defined fermentation differently from how you did, but that is a secondary matter.

With respect to what Arkcon said, there are two ATPs produced per one glucose in the Krebs' cycle itself; each glucose produces two acetyl groups, meaning that one turn of the cycle consumes one acetate and produces one ATP.  However, the bulk of the ATP is made because reactions that feed into or are part of the Krebs's cycle produce a great deal of NADH and FADH₂. 

[Borek]

I strongly suspect that microorganisms are not too dissimilar.

I can be very off here, but I believe all microorganism that have no mitochondria (which means all procaryota) produce ATP quite slowly and are in many ways limited by the fact. One of the effects is that while eucaryota are for all practical reasons not limited in the amount of the DNA they contain (hence a lot of non-coding and junk DNA in our cells), bacteria multiply faster when they have to replicate lower number of genes (hence short DNA, containing the minimum of necessary genes, is favored by the evolution).

[Babcock_Hall]

From a 1971 article in J. Bacteriology 108(3), p. 1072-86
Abstract
The value of the adenylate energy charge, [(adenosine triphosphate) + ½ (adenosine diphosphate)]/[(adenosine triphosphate) + (adenosine diphosphate) + (adenosine monophosphate)], in Escherichia coli cells during growth is about 0.8. During the stationary phase after cessation of growth, or during starvation in carbon-limited cultures, the energy charge declines slowly to a value of about 0.5, and then falls more rapidly. During the slow decline in energy charge, all the cells are capable of forming colonies, but a rapid fall in viability coincides with the steep drop in energy charge. These results suggest that growth can occur only at energy charge values above about 0.8, that viability is maintained at values between 0.8 and 0.5, and that cells die at values below 0.5. Tabulation of adenylate concentrations previously reported for various organisms and tissues supports the prediction, based on enzyme kinetic observations in vitro, that the energy charge is stabilized near 0.85 in intact metabolizing cells of a wide variety of types.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC247190/

Table 13-5 (p. 518) in Lehninger Principles of Biochemistry gives the ATP, ADP, and AMP concentrations for four eukaryotic and one bacterial (E. coli) cell.  The energy charge could be computed from these values, but I am short on time just now.  In all cases [ATP] > [ADP] > [AMP].  I do not know about the relative speeds of ATP production.  However, bacteria obtain slightly higher amounts of ATP per glucose than an typical eukaryote does.  My point is that all organisms regulate catabolism and anabolism in such a way as to maintain a high level of ATP relative to ADP and P_i.  One way to think about this is to realize that the amount of work obtained from the hydrolysis of ATP is dependent on the value of ΔG, not ΔG°.  If ATP fell to a sufficiently low level, ΔG would be zero.