unsaturated and free fatty acids that are typically reported in the cell membranes of
psychrophilic bacteria are also related to the low-temperature environment.
11.2.2 Halophilic Microorganisms
Seawater has salt content of roughly 3.5%, and the microorganisms that inhabit the
oceans are capable of growth even in the presence of high saline concentrations.
Marine bacteria typically flourish at concentrations of 0.3–0.8 mol NaCl. Some
bacteria require a high salt concentration to survive, such as those that live in the
Dead Sea in the Middle East or the Great Salt Lake in North America, both of
which have higher saline concentrations than seawater.
While marine and land bacteria may be distinguished by examining the relationship between salt concentration and growth, marine bacteria can also be identified simply through placement in distilled water. The cell walls of marine bacteria
will rupture in the presence of pure water containing no salt, as they cannot regulate
osmotic pressure.
When salt concentration within the cell is higher than outside, the imbalance
typically leads to water gradually entering the cell from outside. The external cell
membrane possesses mechanisms for allowing only what is needed within the cell
and blocking unnecessary things from entering. Low molecular weight substances
like water are not regulated by these mechanisms, and water permeates the cell
through physical diffusion. As a result, the outward pressure exerted within the cell
increases and the cell bursts.
The NaCl that marine bacteria require for growth is not needed for osmotic
pressure regulation. Whereas a non-halophilic bacterium obtains energy through the
movement of protons (H
+
) in and out of the cell membrane, marine bacteria have
developed mechanisms to harness energy from the movement not only of protons,
but also of the sodium ions in NaCl (Margesin and Schinner 2001).
Because seawater possesses roughly 3.5% salt content, most marine bacteria
cannot propagate at a 0% concentration, and propagate best at concentrations
equivalent to those in seawater, as shown in Fig. 11.3. In contrast, land-bacteria
typically exhibit maximum growth at a 0% salt concentration, and their growth is
inhibited as the salt concentration rises.
Fish sauce is an example of a fermented food made through the industrial
application of halophilic bacteria. Fish sauce is a nutrient-rich fermented condiment
made by adding salt to hydrolyze the fish’s flesh with protein-dissolving enzymes
located inside the fish’s viscera. The forms marketed in Korea, Japan, and Southeast
Asia are made by traditional methods, but their commercial potential is diminished
by the fact that the process takes a long period of 6–18 months. One approach that
could be applied commercially to produce fish sauce quickly is the use of
protein-dissolving enzymes extracted from media obtained through mass culturing
of halophilic bacteria from seawater; adding these enzymes to fish such as sardines
will result in flesh being broken down relatively easily (Imada 2009).
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11 Marine Microorganism Resources and Biotechnology
psychrophilic bacteria are also related to the low-temperature environment.
11.2.2 Halophilic Microorganisms
Seawater has salt content of roughly 3.5%, and the microorganisms that inhabit the
oceans are capable of growth even in the presence of high saline concentrations.
Marine bacteria typically flourish at concentrations of 0.3–0.8 mol NaCl. Some
bacteria require a high salt concentration to survive, such as those that live in the
Dead Sea in the Middle East or the Great Salt Lake in North America, both of
which have higher saline concentrations than seawater.
While marine and land bacteria may be distinguished by examining the relationship between salt concentration and growth, marine bacteria can also be identified simply through placement in distilled water. The cell walls of marine bacteria
will rupture in the presence of pure water containing no salt, as they cannot regulate
osmotic pressure.
When salt concentration within the cell is higher than outside, the imbalance
typically leads to water gradually entering the cell from outside. The external cell
membrane possesses mechanisms for allowing only what is needed within the cell
and blocking unnecessary things from entering. Low molecular weight substances
like water are not regulated by these mechanisms, and water permeates the cell
through physical diffusion. As a result, the outward pressure exerted within the cell
increases and the cell bursts.
The NaCl that marine bacteria require for growth is not needed for osmotic
pressure regulation. Whereas a non-halophilic bacterium obtains energy through the
movement of protons (H
+
) in and out of the cell membrane, marine bacteria have
developed mechanisms to harness energy from the movement not only of protons,
but also of the sodium ions in NaCl (Margesin and Schinner 2001).
Because seawater possesses roughly 3.5% salt content, most marine bacteria
cannot propagate at a 0% concentration, and propagate best at concentrations
equivalent to those in seawater, as shown in Fig. 11.3. In contrast, land-bacteria
typically exhibit maximum growth at a 0% salt concentration, and their growth is
inhibited as the salt concentration rises.
Fish sauce is an example of a fermented food made through the industrial
application of halophilic bacteria. Fish sauce is a nutrient-rich fermented condiment
made by adding salt to hydrolyze the fish’s flesh with protein-dissolving enzymes
located inside the fish’s viscera. The forms marketed in Korea, Japan, and Southeast
Asia are made by traditional methods, but their commercial potential is diminished
by the fact that the process takes a long period of 6–18 months. One approach that
could be applied commercially to produce fish sauce quickly is the use of
protein-dissolving enzymes extracted from media obtained through mass culturing
of halophilic bacteria from seawater; adding these enzymes to fish such as sardines
will result in flesh being broken down relatively easily (Imada 2009).
386
11 Marine Microorganism Resources and Biotechnology