0003 bm md 3 lect 05 bacteria growt nutn 17 09 2014 wed to send

8/10/2019 0003 BM MD 3 Lect 05 Bacteria Growt Nutn 17 09 2014 Wed to Send

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Bacteria:

Growth and Nutrition



Objective:

To learn about how bacteria derive their nutrition

natural environment

Their cultivation in the laboratory

Different phases of bacterial growth and its meas



Growth Cycle

• Bacteria reproduce by binary fission

• Because one cell gives rise to two progeny cells, bacter

to undergo exponential growth (logarithmic growth)



Growth Cycle

• The concept of exponential growth can be illustrated by

following relationship:

• Thus, 1 bacterium will produce 16 bacteria after 4 gene



The Doubling (Generation) Time of

• Escherichia coli - 20 minutes

One E. coli will produce over 1000 progeny in about 3

over one million in about 7 hours

• Mycobacterium tuberculosis - more than 24 hours

• The doubling time varies with: speciesthe amount of nutrient

temperature

pH, and

other environmental fa



• The growth cycle of bacteria has

four major phases:

1. Lag phase - vigorous metabolic activity

occurs but cells do not divide

- Last for a few minutes up to many

hours

2. Log (logarithmic) phase - is when rapid

cell division occurs

Growth Cycle

Growth curve of bacteri

phase; c, stationary pha

• Lactam drugs, such as

log phase because the d

when cells are making p

when they are dividing



3. Stationary phase: Due to exhaustion of

nutrients or accumulation of toxic products

death of bacteria starts and the growth cease

completely

- The count remains stationary due to balance

between multiplication and death rate

4. Death phase: marked by a decline in the

number of viable bacteria

Growth Cycle

Growth curve of bacteri

phase; c, stationary pha



• Chemical nutrients such as carbon,

hydrogen, oxygen, and nitrogen are required

for the growth of microbial populations



Bacteria are categorized according to their

related behavior



a. Facultative Anaerobes: These bacteria can oxidize nutrient substrates by m

respiration and fermentation - E. coli

b. Obligate Aerobes: oxygen is essential, because it serves as the final electro

electron transport chains e.g. M. tuberculosis

c. Obligate Anaerobes: These bacteria die in the presence of oxygen - Clostrid

d. Aerotolerant anaerobes : Do not use aerobic metabolism, but tolerate oxy

e.g. Lactobacilli

e. Microaerophiles: require oxygen levels of 2% to 10% e.g. Helicobacter pylo

• Microaerophiles are damaged by the 21% concentration of oxygen in the at

• Have limited ability to detoxify hydrogen peroxide and superoxide radicals



Why Anaerobes are Susceptible to Ox

• Superoxide ion (O2−), H2O2, and hydroxyl radicals (OH−) are destru

metabolic by-products of oxygen

• Obligate aerobes and facultative anaerobes usually contain supedismutase and either catalase or peroxidase enzymes

• Obligate anaerobes lack those enzymes

• Therefore cannot tolerate any free oxygen in the immediate enviwill die if exposed to it



Categories of organisms based on the

carbon and energy sources



• Autotrophs: ‘feed themselves’• Utilize an inorganic source of carbon (carbon dioxide) as their

of carbon

Organisms can be categorized into two broad groups ba

their source of Carbon:

• Heterotrophs:

• Catabolize reduced organic molecules (proteins, carbohydrate

acids, and fatty acids) they acquire from other organisms

• Include parasitic bacteria



1. Chemotrophs:

• Acquire energy from redox reactions involving inorganic and

chemicals

• Redox reactions are either aerobic respiration, anaerobic resor fermentation

Organisms categorized according to whether they use c

or light as a source of energy for anabolism, intracellula

transport, and motility:

• Phototrophs: Use light as their energy source



Four basic groups of organisms based on their car

energy sources

F t i f i b b d T t



Four categories of microbes based on Temperature

growth

Microbiology : with

0003 bm md 3 lect 05 bacteria growt nutn 17 09 2014 wed to send

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