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Growth requirements
Optimal Conditions –
Conditions in witch bacteria thrive.
A. Warmth
B. Moisture
C. Food
D. Gases – usually oxygen
Growth Requirements
Sources of carbon, energy, and electrons
– Two groups of organisms based on source of carbon
• Autotrophs
• Heterotrophs
– Two groups of organisms based on source of energy
• Chemotrophs
– Phototrophs
Figure 6.1 Four basic groups of organisms
Growth Requirements
Oxygen requirements
– Aerobes - are completely dependent on atmospheric O2 for
growth
– Anaerobes - do not tolerate O2 and die in its presence
– Facultative anaerobes - do not require O2 for growth, but do grow
better in its presence
– Aerotolerant anaerobes - ignore O2 and grow equally well
whether it is present or not
– Microaerophiles - are damaged by the normal atmospheric level
of O2 (20%) but require lower levels (2 to 10%) for growth
Figure 6.3 Oxygen requirements of organisms-overview
Growth Requirements
Nitrogen requirements
– Nitrogen fixation by certain bacteria is essential to life on Earth
– Nitrogen acquired from organic and inorganic nutrients
Key bacteria for nitrogen cycle
• Nitrosomonas convert ammonia to nitrite
• Nitrobacter convert nitrite to nitrate.
• Pseudomonas convert nitrate to nitrogen gas.
• Azotobacter and Rhizobium are nitrogen-fixing bacteria
which fix nitrogen from the atmosphere and make it available
to leguminous plants
Growth Requirements
Other chemical requirements
– Phosphorus
– Sulfur
– Trace elements
• Required only in small amounts
– Growth factors
• Necessary organic chemicals that cannot be
synthesized by certain organisms
Growth Requirements
• Physical Requirements
– Temperature
• Effect of temperature on proteins
• Effect of temperature on membranes of cells and
organelles
– If too low, membranes become rigid and fragile
– If too high, membranes become too fluid
Figure 6.4 Microbial growth-overview
• Psychrophile - cold‐loving, having an optimal
temp. at about 15°C or lower
– max temperature = about 20°C
• Mesophile - moderate temp, between 20 and
45°C
• Thermophile - high temperatures, between 41
and 122 °C
• Hyperthermophile - extremely hot environments,
from 60 °C (140 °F) upwards
– optimal temperature is above 80 °C
Figure 6.5 Four categories of microbes based on temperature ranges for growth
Growth rate
Thermophiles
Mesophiles
Psychrophiles
Temperature (°C)
Hyperthermophiles
Figure 6.6 An example of psychrophile-overview
Growth Requirements
• Physical Requirements
– pH
• Organisms are sensitive to changes in acidity
– H+ and OH– interfere with H bonding
• Neutrophiles grow best in a narrow range around
neutral pH (5.5 – 8.0)
• Acidophiles grow best in acidic habitats
– pH between 0-5.5
• Alkalinophiles live in alkaline soils and water
– pH between 8.5 and 11.5
Growth Requirements
• Physical Requirements - water
– Most cells die in absence of water
• Some have cell walls that retain water
• Endospores and cysts cease most metabolic activity
– Hydrostatic pressure
• Water exerts pressure in proportion to its depth
• Barophiles live under extreme pressure
– Their membranes and enzymes depend on pressure to maintain
their shape
Growth Requirements
• Physical Requirements - water
– Osmotic pressure
• Hypotonic - osmotic lysis can occur
• Hypertonic - cell shrinkage called plasmolysis
– the addition of salts or other solutes to a solution inhibits
food spoilage by bacteria
– as occurs when meats or fish is salted
• Restricts organisms to certain environments
– halophiles
Associations and Biofilms
• Organisms live in association with different
species
– Antagonistic relationships
– Synergistic relationships
– Symbiotic relationships
Associations and Biofilms
• Biofilms – complex relationships among many
microorganisms
– Develop an extracellular matrix
•
•
•
•
Adheres cells to one another
Allows attachment to a substrate
Sequesters nutrients
May protect individuals in the biofilm
– Form on surfaces often as a result of quorum sensing
• a system of stimulus and response correlated to population
density
• coordinate gene expression according to the density of their local
population
– Many microorganisms more harmful as part of a biofilm
Figure 6.7 Plaque (biofilm) on a human tooth