Science of Water : Concepts and Applications

Water Biology 133
or lamellae. Their exact function is unknown. Currently, many bacteriologists believe that mesosomes
are artifacts generated during the fi xation of bacteria for electron microscopy.
Nucleoid (Nuclear Body or Region)
The nuclear region of the prokaryotic cell is primitive and a striking contrast to that of the
eukaryotic cell (see Figure 5.3). Prokaryotic cells lack a distinct nucleus; the function of the nucleus
is carried out by a single, long, double-stranded DNA that is effi ciently packaged to fi t within the
nucleoid. The nucleoid is attached to the plasma membrane. A cell can have more than one nucleoid
when cell division occurs after the genetic material has been duplicated.
Ribosomes
The bacterial cytoplasm is often packed with ribosomes (see Figure 5.3). Ribosomes are minute,
rounded bodies made of RNA and are loosely attached to the plasma membrane. Ribosomes are
estimated to account for about 40% of a bacterium’s dry weight; a single cell may have as many
as 10,000 ribosomes. Ribosomes are the site of protein synthesis and are part of the translation
process.
Inclusions
Inclusions (or storage granules) are often seen within bacterial cells (see Figure 5.3). Some inclusion
bodies are not bound by a membrane and lie free in the cytoplasm. A single-layered membrane
about 2–4 µm thick encloses other inclusion bodies. Many bacteria produce polymers that are stored
as granules in the cytoplasm.
BACTERIAL GROWTH FACTORS
Several factors affect the rate at which bacteria grow, including temperature, pH, and oxygen levels.
The warmer the environment, the faster the rate of growth. Generally, for each increase of 10°C, the
growth rate doubles. Heat can also be used to kill bacteria.
Most bacteria grow best at neutral pH. Extreme acidic or basic conditions generally inhibit
growth, though some bacteria may require acidic and some require alkaline conditions for growth.
Bacteria are aerobic, anaerobic, or facultative. If aerobic, they require free oxygen in the aquatic
environment. Anaerobic bacteria exist and multiply in environments that lack dissolved oxygen.
Facultative bacteria (e.g., iron bacteria) can switch from an aerobic to anaerobic growth or grow in
an anaerobic or aerobic environment.
Under optimum conditions, bacteria grow and reproduce very rapidly. As stated previously,
bacteria reproduce by binary fi ssion.
An important point to consider in connection with bacterial reproduction is the rate at which
the process can take place. The total time required for an organism to reproduce and the offspring
to reach maturity is called generation time. Bacteria growing under optimal conditions can double
their number about every 20 min. Obviously, this generation time is very short compared with that
of higher plants and animals. Bacteria continue to grow at this rapid rate as long as nutrients hold
out—even the smallest contamination can result in a sizable growth in a very short time.
√ Note: Even though wastewater can contain bacteria counts in the millions per milliliter, in
wastewater treatment, under controlled conditions, bacteria can help destroy and identify
pollutants. In such a process, bacteria stabilize organic matter (e.g., activated sludge processes),
and thereby assist the treatment process in producing effl uent that does not impose an excessive
oxygen demand on the receiving body. Coliform bacteria can be used as an indicator of pollution
by human or animal wastes.