Conditions to Promote Bacterial Growth

Although all bacteria require energy, nutrients and appropriate physical conditions (e.g., temperature, oxygen concentration and pH) to grow, there is no single set of conditions under which all bacteria will grow.

Nutrients

• In the lab, scientists may use a chemically defined medium or a complex medium to provide nutrients to grow bacteria. Chemically defined media contain biochemicals from a chemical manufacturer, and complex media contain materials such as blood, milk, yeast extract or beef extract. Some bacteria require specialized nutrition that they can only obtain from their natural host cells, so they cannot be grown in a lab.

pH

• Acidophiles grow optimally at a pH below 7.0, neutrophiles at 7.0 and alkaliphiles above 7.0.

Temperature

• Mesophiles grow best near 37 degrees Celsius, thermophiles thrive between 45 and 70 degrees Celsius and hyperthermophiles have a optimum growth temperature over 80 degrees Celsius. There are also cold-loving bacteria, called psychrophiles, which have an optimum temperature of 10 to 15 degrees Celsius.

Salt

• Halophiles need salt (NaCl) to grow; halotolerant bacteria can grow in the presence of salt but grow better without it.

Energy

• Phototrophs use light as an energy source. Heterotrophs or (chemo)heterotrophs get energy from organic carbon. Lithotrophs oxidize inorganic compounds to get energy.