The document discusses several topics related to bacterial physiology: 1) The minimum nutritional requirements for bacterial growth including carbon, nitrogen, hydrogen, oxygen, and inorganic salts. 2) Bacterial growth curves which show four phases: lag, log, stationary, and decline. Metabolic activity and cell division occur at different rates in each phase. 3) Factors that affect bacterial growth such as oxygen requirements, temperature tolerance, pH tolerance, moisture, and energy source. Obligate aerobes require oxygen while obligate anaerobes cannot tolerate it.

1. PHYSIOLOGY
OF BACTERIA

2. BACTERIAL GROWTH REQUIREMENT
The minimum nutritional requirements that are essential for growth and
multiplication of bacteria include :---
• Carbon
• Nitrogen
• Hydrogen
• Oxygen
• Some inorganic salts ( sulfur , phosphorus and other elements like sodium ,
potassium , magnesium , iron and manganese )

3. BACTERIAL VITAMIN
Bacterial vitamins are same as the vitamin necessary for mammalian nutrition , particularly those
belonging to the vitamin B group – thiamine , nicotinic acid , riboflavin , pyridoxine , folic acid
and vitamin B12 .
VITAMINS BACTERIA REQUIRING
Biotin Leuconostoc species
Cyanocobalamin (B12) Lactobacillus species
Folic Acid Enterococcus faecalis
Pantothenic Acid Morganella morganii
Pyridoxine (B6) Lactobacillus species
Niacin (Nicotinic Acid) Brucella abortus , Haemophilus
influenzae
Riboflavin(B2) Bacillus anthracis

4. BACTERIAL CELL DIVISION
Bacteria divide by a relatively simple form of cell division , i.e. by binary division . The nuclear
division precedes cytoplasmic division .
 Nuclear division : The two strands of bacterial DNA are separated and then replicate to form
new complimentary strands . Thus two identical molecules of ds DNA are formed .
 Cytoplasmic division : A transverse septum grows across the cell from the cell membrane ,
following which the cell wall materials are deposited and then two daughter cells get
separated.
 In few bacteria , the daughter cells may remain partially attached even after cell division ; so
that the bacterial cells are arranged in pair or in chain (e.g. streptococcoi) or in clusters (e.g.
staphylococci) .

5. RATE OF MULTIPLICATION IN BACTERIA
Generation time is the time required for a bacterium to give rise to two
daughter cells under optimum condition .
The generation time for different bacteria is as follows :
 Eschericia coli and most of the other pathogenic bacteria : 20 minutes
 Mycobacterium tuberculosis : 10 -15 hours
 Mycobacterium leprae : 12 – 13 days

6. BACTERIAL GROWTH CURVE
When a bacterium is inoculated into a suitable liquid culture medium and incubated , its growth follows a
definite course . When bacterial count of such culture is determined at different intervals and plotted in
relation to time , a bacterial growth curve is obtained comprising of four phases :
1) Lag phase: -- a) bacteria increases in size due to accumulation of enzymes and metabolites.
b) bacteria reach their maximum size at the end of lag phase .
2) Log phase : -- a) smaller in size
b) biochemically active : it is the best stage to perform the biochemical reactions.
c) uniformly stained : it is the best time to perform gram stain .
3) Stationary phase :-- a) bacterium becomes gram-variable.
b) more storage granules are formed .
c) sporulation occurs in this phase .
d) bacteria produces exotoxins , antibiotics and bacteriocins .
4) Decline phase :-- a) there is decline in viable count and not in total count
b) involution forms are seen .

7. BACTERIAL GROWTH CURVE
This Photo by Unknown Author is licensed under CC BY
Total count
Viable count

8. VARIOUS PHASES OF BACTERIAL GROWTH CURVE
Lag Log Stationary Decline
Bacterial divide No Yes Yes No
Bacterial death No No Yes Yes
Total count Flat Raises Raises Flat
Viable count Flat Raises Flat Falls
Special features Accumulation of
enzymes and
metabolites
Attains maximum
size
Uniformly stained
Metabolically active
Small size
Gram variable
Produce : granules
spores ,exotoxin ,
antibiotics ,
bacteriocin .
Produce :
Involution forms .

9. FACTORS AFFECTING GROWTH OF BACTERIA
There are several environmental factors that affect the growth of the bacteria .
Oxygen :- on the basis of their oxygen requirements bacteria are classified as:
 Obligate aerobes : - they can grow only in the presence of oxygen ( e.g. Pseudomonas ,
Mycobacterium tuberculosis , Bacillus , Brucella and Nocardia).
 Facultative anaerobes : they are aerobes that can also grow anaerobically (e.g. most of the
pathogenic bacteria , e.g. E.coli , S. aureus )
 Facultative aerobes : they are anaerobes that can also grow aerobically (e.g. Lactobacillus)
 Microaerophilic bacteria : they can grow in the presence of low oxygen tension i.e. 5-10% of
oxygen ( e.g. Campylobacter and Helicobacter)
 Obligate anaerobes : these bacteria can grow only in the absence of oxygen, as oxygen is
lethal to them ( e.g. Clostridium)
 Aerotolerant anaerobes : they can tolerate oxygen for some time , but do not use it (
Clostridium histolyticum)

10. CONTD.
Carbon Dioxide :- organisms that require higher amount of carbon
dioxide (5-10%) for growth are called capnophilic bacteria. Example : Brucella
abortus , Streptococcus pneumoniae etc.
Temperature :--
 Psychrophiles :- Grow best at temperatures below 20 degree Celsius ; example ,
most of the saprophytes , e.g. Pseudomonas.
 Mesophiles :- these grow within a temperature range 25 degree Celsius and 40
degree Celsius ; example , most of the pathogenic bacteria
 Thermophiles : - these bacteria grow at a high temperature range of 55 degree
Celsius – 80 degree Celsius , e.g. Geobacillus stearothermophilus .

11. CONTD.
pH : most pathogenic bacteria between pH 7.2 – pH 7.6 . Very few bacteria (
e.g. lactobacillus) can grow at acidic pH below pH 4 , while bacteria such as
Vibrio cholerae are capable of growing at alkaline pH (8.2 – 8.9) .
Light :- except phototrophs , bacteria grow well in darkness . Photochromatic
mycobacteria pigments only exposure to light .
Moisture and desiccation :- moisture is an essential requirement for the
growth of the bacteria because 80% of the bacterial cell consists of water .
However , the drying has varying effects on different organisms .
 Some organisms like Treponema pallidum and tuberculosis and
Staphylococcus aureus may survive drying for several weeks .

12. CLASSIFICATION BASED ON ENERGY REQUIREMENTS
 Phototrophs :- bacteria that derive energy from sunlight
 Chemotrophs :- bacteria that derive energy from chemical reactions .
 Autotrophs :- Bacteria that synthesise their own organic material .
 Heterotrophs :- Bacteria that cannot synthesise their metabolites ; they
utilize atmospheric carbon dioxide and nitrogen.

13. METABOLISM OF PATHOGENIC BACTERIA
The bacterial metabolism is dependent on whether they are aerobic or
anaerobic .
 Aerobic bacteria utilize glucose by oxidation
 The anaerobes utilize glucose by fermentation.
FERMENTATION :- Bacterial fermentation occurs via three pathways :
1) Glycolysis
2) Entner – Doudroff (ED) pathway
3) Pentose phosphate pathway
OXIDATION :- oxidation refers to oxidative utilization of glucose (by Krebs
Cycle) followed by production of ATP via oxidative phosphorylation and transfer
transfer of electrons in electron transport system .