FoodBanter.com - life cycle of bacteria and funghi

On Dec 5, 4:35*pm, padriac > wrote:
> I was asked what the life cycle of bacteria and fungi in sourdough
> culture was, ie how long did they live, and how did they reproduce. I
> dont know the answer can anyone help? Paddy

That's not a straight-forward answer, as the bacteria and yeast in
sourdough are quite variable, divide through different ways, and live
for different lengths of time. Not only that, but temps, pH, and a
whole other range of conditions can change the answer.

In terms of how the reproduce, most of the bacteria do it through
binary fission; the cell duplicates everything it needs and then
splits in half. Yeast generally reproduce by budding; basically the
new cell forms as a small "bud" on the side of the mother cell, and
the bud is subsequently released. That said, some types of yeast
divide by binary fission, just like bacteria.

Yeast reproduction is further complicated by the fact that yeast can
reproduce asexually (i.e. the division produces a photocopy of the
mother cell) and sexually (i.e. the yeast join their genetic material
with another yeast, before reproducing). Exactly how much of asexual
vs. sexual reproduction you'll get varies based on the exact strains
of yeast in your starter and the growing conditions.

Bacteria can also engage in a limited form of "sex", in that some
bacteria have ways of passing DNA between each other. Once again,
whether or not this occurs in your starter will depend on the bacteria
present and the growing conditions.

As for lifespan, that is not as cut-and-dried a question as you may
think. Since these organisms reproduce by dividing themselves, it
isn't exactly clear which new cell is the "child" and which the
"parent". As such lifespan is not always easy to define with these
organisms. One can even take the point-of-view that any single-celled
organism is as "old" as the species - several million years in the
case of most of the bacteria/yeast that you'll find in your culture -
simply because every cell alive today is a product of divisions going
all the ways back to the first cell of the species. Those caveats
aside, the generation time (i.e. time from one cell division to
another) is generally going to be between 30min and 1-2hrs in a fresh
starter. As the starter is consumed, the generation time will get
longer and longer. Eventually the bacteria/yeast will run out of food
and go into dormancy. Depending on the bacteria/yeast, and the form
of dormancy they go into, that dormant state may be stable for years,
decades, even centuries.

Bryan