Bacterial Temperature Tolerance

Study Notes

Temperature

Psychrotrophs can grow at 0°C and have an optimum temperature of 20-30°C, found in soil, water, milk, and dairy products, e.g. Listeria monocytogenes.
Mesophiles are most bacteria associated with human infection, growing optimally between 9 and 40°C.
Thermophiles grow at 55°C or higher, found in compost, hay stacks, hot water lines, and hot springs, with more heat-stable enzymes and protein synthesis systems.
Hyperthermophiles can grow at 90°C or 100°C, found in hot areas of the sea floor.

Bacteria and Oxygen

Aerobes are capable of growth in full oxygen tension (21% in the atmosphere), using oxygen as a terminal receptor for electron transport chain in aerobic respiration.
Anaerobic organisms lack a respiratory system that can use oxygen, with obligate anaerobes being killed by oxygen, and facultative anaerobes able to decompose toxic oxygen products.
Microaerophiles are anaerobes that can tolerate oxygen and grow in its presence, but do not use it.
Strict anaerobes are killed by oxygen but can be found in otherwise aerobic environments, e.g. the mouth.

Bacterial Culture Media

Understanding growth requirements helps in designing culture media for a given genera and enables selectivity.
Knowledge of metabolic pathways helps in designing identification systems/media.

Environmental Factors Affecting Bacterial Growth

Source of nitrogen, carbon, essential ions, and nutrients.
Temperature.
Water, salt levels.
pH.
Atmosphere (O2 levels).

Essential Elements

Carbon, oxygen, nitrogen, hydrogen, sulphur, phosphorous, potassium, magnesium, calcium, iron, sodium, and chloride.
Bacteria can synthesise molecules called siderophores to sequester iron from host iron stores.

Salt (Osmolarity)

Halophiles have adapted to higher salt levels (seawater has 3% salt), requiring salt levels of 2.8M to saturation of 6.2M.
Halophiles modify structure of proteins and membranes, and extreme halophiles accumulate levels of potassium to remain hypertonic (4–7M).
Halotolerant bacteria can tolerate some reduction in salt levels.

Water

80% or more of the cell mass is water, which is essential for growth.
Free available water (A) is necessary for nutrients and waste products to enter and leave the cell.

Effect of pH

Most environments have a pH of between 5 and 8-9, and most organisms grow within these parameters.
Acidophiles grow optimally between pH 0 and 5.5.
Neutrophiles grow between pH 5.5 and 8.
Alkalophiles grow between pH 8.5-11, with extreme alkalophiles at pH 10 or above.
Most bacteria and protozoa are neutrophiles, while fungi require slightly acid conditions (pH 4-6), and algae favour acidity.

Description

This quiz covers the different types of bacteria classified by their optimal growth temperatures, including psychrotrophs, mesophiles, thermophiles, and hyperthermophiles. Learn about the characteristics and habitats of each type.