GCMP2022 INTRODUCTION TO BACTERIA

NUCLEUS (NUCLEOID)

• Nucleus is the most important part of the cell.
• It controls and directs all the cellular activities and

stores hereditary information of cell
• Bacterial nucleus is known as nucleoid; it lacks

nuclear membrane, nuceloplasm and nucleolus.

NUCLEUS (NUCLEOID)

• Bacterial DNA is naked (lacked histone protein)
• Function:

– It contains and stores hereditary information of
the cell.

– It controls all cell activities.



RIBOSOME

• Bacterial ribosome is of 70s type.
• Ribosomes are rounded granules found freely

floating in the cytoplasm
• Ribosomes are known as universal cell organelle

because it is found in both bacterial cell and
eukaryotic cell.

RIBOSOME

• Chemically the ribosomes are made up of nucleic
acids (particularly RNA and proteins).

• Function:
– It helps in protein synthesis



MESOSOME

• Mesosome is a spherical or round sac like structure
found commonly in gram positive bacteria.

• Function:
– It is the site for respiration in bacterial cell



CYTOPLASM

• It is colorless, viscus fluid present inside cell
membrane.

• All the cell organelles and inclusions are found
floating in cytoplasmic fluid.

• It contains proteins, lipid, minerals, nucleic acids,
glycogen, water etc.

CYTOPLASM

• Function:
– It helps to distribute water, oxygen as other
substances throughout the cell.
– Literally, all the cellular content including nucleus,
and other cell organelle are floating in cytoplasm.

SPORE (ENDOSPORE)

• Spore is metabolically dormant structure produced
during unfavourable condition by the process called
sporulation

• Sporulation occur during late log phase or early
stationary phase

• Under favourable condition spores germinate to give
vegetative cell.



IMPORTANCE OF BACTERIA

• Not all bacteria are harmful to humans. There are some
bacteria which are beneficial in different ways. Listed below
are few benefits of bacteria:
• Convert milk into curd – Lactobacillus or lactic acid bacteria
• Ferment food products – Streptococcus and Bacillus
• Help in digestion and improving the body’s immunity
system – Actinobacteria, Bacteroidetes, Firmicutes,
Proteobacteria
• Production of antibiotics, which is used in the treatment
and prevention of bacterial infections – Soil bacteria

FACTORS INFLUENCE GROWTH
AND REPRODUCTION OF
ORGANISM

PHYSICAL CHEMICAL
FACTORS FACTORS

PHYSICAL FACTORS

• Temperature
• pH
• Osmotic Pressure
• Hydrostatic Pressure
• Radiation

TEMPERATURE

PSYCHROPHILES MESOPHILES THERMOPHILES

Cold loving organism Warm Heat loving organism
50oC to 60oC
15oC to 20oC (can live quite 25oC to 40oC (cannot live
well at 0oC) more than 40oC)

Obligate psychrophiles Most of human pathogen Obligate thermophiles can

cannot grow above 20oC are in this group live above 37oC only

Facultative psychrophiles Facultative thermophiles,
grow best below 20oC also which can grow both above

can grow above 20oC and below 37oC

TEMPERATURE

The temperature range over which an organism grows is determined
largely by the temperatures at which its enzymes function. Within this
temperature range, three critical temperatures can be identified:
1. The minimum growth temperature, the lowest temperature at

which cells can divide.
2. The maximum growth temperature, the highest temperature at

which cells can divide.
3. The optimum growth temperature, the temperature at which cells

divide most rapidly—that is, have the shortest generation time.

TEMPERATURE

• Temperature is important not only in providing conditions for
microbial growth, but also in preventing such growth.

• The refrigeration of food, usually at 4oC, reduces the growth of
psychrophiles and prevents the growth of most other bacteria.

• However, food and other materials, such as blood, can support
growth of some bacteria even when refrigerated. For this reason,
perishable materials that can withstand freezing are stored at
temperatures of 30oC if they are to be kept for long periods of time.

TEMPERATURE

• High temperatures also can be used to prevent bacterial growth.

• Laboratory equipment and media are generally sterilized with heat,
and food is frequently preserved by heating and storing in closed
containers.

• Bacteria are more apt to survive extremes of cold than extremes of
heat; enzymes are not denatured by chilling but can be
permanently denatured by heat.

TEMPERATURE

• Cold temperatures may have helped to preserve Exiguobacterium
sp., a bacterium isolated from 2- to 3-million-year-old Siberian
permafrost soil.

• It grows well at 2.5oC and is associated with human infections. And,
contrary to expectations, soil-dwelling fungi in mountainous parts
of the United States have been found to increase in numbers and
biomass beneath the ice and snow of winter, compared to their
abundance in summer.

pH

• Microorganisms have an optimum pH—the pH at which they grow
best. Their optimum pH is usually near neutrality (pH 7).

• Most microbes do not grow at a pH more than 1 pH unit above or
below their optimum pH

• According to their tolerance for acidity or alkalinity, bacteria are
classified as: acidophiles, neutrophiles and / or alkaliphiles

pH

ACIDOPHILES NEUTROPHILES ALKALIPHILES

Acid-loving organism Normal Alkali-loving organism

Grow best at a pH 0.1 to 5.4 5.4 to 8.0 7.0 to 11.5
Most of bacteria that cause
Lactobacillus, which produces Vibrio cholerae, the causative
lactic acid, is an acidophile, but disease in human agent of the disease Asiatic
cholera, grows best at a pH of
it tolerates only mild acidity. about 9.0. Alcaligenes faecalis,
Some bacteria that oxidize
which sometimes infects
sulfur to sulfuric acid, humans already weakened by
however, can create and another disease, can create
tolerate conditions as low as
and tolerate alkaline
pH 1.0. conditions of pH 9.0 or higher.

OSMOTIC PRESSURE

• Osmotic pressure is the pressure that needs to be applied to a
solution to prevent the inward flow of water across a
semipermeable membrane.

• The cell membrane allows water to move by osmosis between the
cytoplasm and the environment. Environments that contain
dissolved substances exert osmotic pressure, and the pressure can
exceed that exerted by dissolved substances in cells.

OSMOTIC PRESSURE

• Cells in such hyperosmotic environments lose water and undergo
plasmolysis (plas-mol`e-sis), or shrinking of the cell. In
microorganisms with a cell wall, the cell or plasma membrane
separates from the cell wall. Conversely, cells in distilled water have
a higher osmotic pressure than their environment and, therefore,
gain water.

• In bacteria, the rigid cell wall prevents cells from swelling and
bursting, but the cells fill with water and become turgid (distended).

HYDROSTATIC PRESSURE

• Bacteria that live at high pressures, but die if left in the laboratory
for only a few hours at standard atmospheric pressure, are called
barophiles.

• It appears that their membranes and enzymes do not simply
tolerate pressure but require pressure to function properly.

• The high pressure is necessary to keep their enzyme molecules in
the proper three-dimensional configuration. Without it, the
enzymes lose their shape and denature, and the organisms die.

RADIATION

• Radiant energy, such as gamma rays and ultraviolet light, can cause
mutations (changes in DNA) and even kill organisms. However,
some microorganisms have pigments that screen radiation and help
to prevent DNA damage. Others have enzyme systems that can
repair certain kinds of DNA damage.

• The bacterium, Deinococcus radiodurans can survive 10,000 Grays
(Gy) of radiation. The Gy is a unit of measurement for absorbed
dose of radiation. 5 Gy will kill a human, and 1,000 Gy will sterilize a
culture of E. coli.

RADIATION

• Bacteria that can withstand high levels of radiation may be valuable
for use in cleaning up contaminated sites.

CHEMICAL FACTORS

Oxygen
Carbon
Nitrogen
Phosphorus
Sulphur

OXYGEN

OXYGEN

• Bacteria, especially heterotrophs, can be divided into aerobes,
which require oxygen to grow, and anaerobes, which do not require
it.

• Aerobes, cultures of rapidly dividing cells require more oxygen than
do cultures of slowly dividing cells. Obligate aerobes, such as
Pseudomonas, which is a common cause of hospital-acquired
infections, must have free oxygen for aerobic respiration, whereas
obligate anaerobes, such as Clostridium botulinum, C. tetani, and
Bacteroides, are killed by free oxygen.

OXYGEN

• Between the extremes of obligate aerobes and obligate anaerobes
are the microaerophiles, the facultative anaerobes, and the
aerotolerant anaerobes.

• Microaerophil (mipkro-aer`o-filz) appear to grow best in the
presence of a small amount of free oxygen. They grow below the
surface of the medium in a culture tube at the level where
oxygen availability matches their needs.

OXYGEN

• Facultative anaerobes ordinarily carry on aerobic metabolism when
oxygen is present, but they shift to anaerobic metabolism when
oxygen is absent.

• Aerotolerant anaerobes can survive in the presence of oxygen but
do not use it in their metabolism.

OXYGEN

• Facultative anaerobes have the most complex enzyme systems.
They have one set of enzymes that enables them to use oxygen as
an electron acceptor and another set that enables them to use
another electron acceptor when oxygen is not available.

• Obligate anaerobes are killed not by gaseous oxygen but by a highly
reactive and toxic form of oxygen called superoxide (O2).

MOISTURE

All actively metabolizing cells generally require a water
environment. Unlike larger organisms that have protective
coverings and internal fluid environments, single celled
organisms are exposed directly to their environment. Most
vegetative cells can live only a few hours without moisture; only
the spores of spore-forming organisms can exist in a dormant
state in a dry environment.

CARBON

Most bacteria use some carbon-containing compound as an
energy source, and many use carbon-containing compounds
as building blocks to synthesize cell components.
Photoautotrophic organisms reduce carbon dioxide to
glucose and other organic molecules. Both autotrophic and
heterotrophic organisms can obtain energy from glucose by
glycolysis, fermentation, and the Krebs cycle. They also
synthesize some cell components from intermediates in
these pathway

NITROGEN

All organisms, including microorganisms, need nitrogen
to synthesize enzymes, other proteins, and nucleic
acids. Many disease-causing organisms obtain amino
acids for making proteins and other nitrogenous
molecules from the cells of humans and other
organisms they invade. Once amino acids are
synthesized or obtained from the medium, they can be
used in protein synthesis.

PHOSPHORUS

Purines and pyrimidines can be used to make DNA and RNA. The
processes by which proteins and nucleic acids are synthesized
are directly related to the genetic information contained in a cell.

SULPHUR

In addition to carbon and nitrogen, microorganisms need a supply of
certain minerals, especially sulfur and phosphorus, which are
important cell components. Microorganisms obtain sulfur from
inorganic sulfate salts and from sulfur-containing amino acids. They
use sulfur and sulfur-containing amino acids to make proteins,
coenzymes, and other cell components. Some organisms can
synthesize sulfur-containing amino acids from inorganic sulfur and
other amino acids. Microorganisms obtain phosphorus mainly from
inorganic phosphate ions. They use phosphorus (as phosphate) to
synthesize ATP, phospholipids, and nucleic acids.

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