Hey man hippy bathday! wait there's no such thing... Happy birthday thats what i meant!;)
I cant give a link to it. Its from the online library from my girlfriends school. im not very comp savvy so ill just cut and paste, read through it and post anything interesting.
Salt and osmotic balance
The salt concentration of microbial environments varies
from distilled water levels to brines and ponds near saturation
(35% for NaCl). Microbes vary in their capacity
to survive and grow in these environments. Halophilic
microbes require at least some NaCl if not other salts for
growth, whereas other microbes cannot survive with
any appreciable salt. Salt curing preserves meat by
inhibiting microbial growth, although some extreme
halophiles can grow even under these conditions.
Extreme halophiles, which include some interesting
types of archaea, can dominate alkaline lakes and evaporation
ponds, coloring the water a brilliant red with
their pigments. The problem facing microbes and all organisms is not
salt per se but the relative amount of water—more precisely,
water activity—in the cell relative to the environment.
With the exception of some extreme halophiles,
water activity is lower and solute concentrations are
higher in a cell than in the external environment, resulting
in the net fl ow of needed water into the cell. This
gradient is relatively easy for cells to maintain in low
salinity environments. However, as salinity increases and
thus water activity decreases, cells face the problem of
retaining water. To do so, they need to raise their internal
solute concentrations by either pumping in inorganic
ions (such as K + ) or by synthesizing organic solutes.
Whether inorganic or organic, these solutes, called the
compatible solutes, must not disrupt normal cellular
biochemical reactions. The compatible organic solutes
include glycine betaine, proline, glutamate, glycerol, and
dimethysulfoniopropionate (DMSP). DMSP is used as a
sulfur source by marine bacteria and can be broken
down to dimethylsulfi de (DMS), which contributes to
negative feedbacks between oceanic biology and climate
change. Figure 3.5 provides examples of organic
compatible solutes.
There are advantages and disadvantages for cells using
organic versus inorganic compatible solutes ( Oren, 1999 ).
Cells using inorganic solutes have to have enzymes and
other proteins specially adapted to high salt concentrations.
In contrast, cells using organic solutes do not need
especially designed enzymes and proteins because
organic compatible solutes are either uncharged or zwitterionic
at the physiological pH. Consequently, only a
few microbes, such as some extreme halophiles, use
inorganic compatible solutes. However, synthesizing
organic solutes is energetically expensive. Energetics may
explain why bacteria and archaea relying on low energyyielding
metabolisms, such as methanogenesis ( Chapter
11 ) and ammonia oxidation ( Chapter 12 ), have not been
isolated from high-saline environments. One organic
solute, glycerol, can be synthesized cheaply but is used
only by some eukaryotes, perhaps because membranes
have to be modifi ed to retain this small, uncharged
molecule.
