Physical Factors Affecting Bacterial Growth-Lesson 11

• • pH
  • temperature
  • oxygen concentration
  • solute concentration

They affect the enzymes which catalyze the metabolic reactions for growth.

An obligate organism must have a particular condition. A facultative organism prefers a particular condition.

Acidophiles are acid-loving bacteria which grow best at a pH between 0.1-5.4.

Neutrophiles are neutral-loving bacteria which grow best at a pH between 5.4-8.8.

Alkalinophiles are alkaline/base-loving bacteria which grow best at a pH between 7.0-11.5.

If the pH becomes more acidic or more basic then this optimum, the protein's 3-D structure tends to change. If the pH is significantly out of the optimum range, it completely loses that structure and flattens out; this is called a denatured protein.

Psychrophiles are cold-loving bacteria and have an optimum temperature range of 15-20 degrees centigrade. These organisms grow on land or in the ocean where temperatures are extremely low. They are also the culprits responsible for the spoilage of refrigerated foods.

Mesophiles are mid temperature-loving bacteria and have an optimum temperature range of 24-40 degrees centigrade. Most of the medically important pathogens are mesophiles and grow well at normal body temperature.

Thermophiles are heat-loving bacteria and have an optimum temperature range of 50-60 degrees centigrade. These organisms are seen in the hot springs or geysers, among other locations in nature. Some extreme thermophiles have temperature optimums closer to 100 degrees centigrade.

Just as was the case with pH, all enzymes have an optimal temperature range at which they function best. Outside of this range, the enzymes will denature and the growth of the organisms will be affected.

Certain organisms possess the enzymes to carry out the metabolic reactions of aerobic respiration. These chemical reactions enable the organisms to catabolize sugars such as glucose to produce energy in the form of molecules of ATP. These bacteria are known as aerobes and they must live in the presence of oxygen. Other organisms possess the enzymes to carry out the reactions of anaerobic respiration, also known as fermentation. These organisms produce smaller quantities of ATP during the catabolism of sugar. These bacteria are known as anaerobes; they do not require oxygen.

Obligate aerobes absolutely require oxygen. These can be cultured on any medium than allows for Oxygen

Microaerophiles need to grow in extremely limited quantities of oxygen and high levels of carbon dioxide, so a Candle Jar is often used for their culture.

Obligate anaerobes grow in the complete absence of oxygen. They do not produce enzymes such as superoxide dismutase or catalase which enable cells to elimate the toxic free radicals superoxide and hydrogen peroxide. Aerotolerant anaerobes can tolerate some oxygen but will die in the presence of more than very small quantities; they still produce energy through anaerobic respiration pathways.
There are several methods of creating anaerobic conditions: physical displacement, chemical displacement or the use of a completely anaerobic jar containing the gaspak system.

Facultatives have the ability to carry out both aerobic and anaerobic respiration reactions and they are known as facultatives. They produce large quantities of ATP when oxygen is available, through aerobic respiration, but can switch to anaerobic respiration when oxygen is lacking. They can be cultured either under aerobic or anaerobic conditions

Osmosis is the movement of water from a higher to lower concentration across a semi-permeable membrane.

hypertonic solution means that it has a high concentration of solutes like salts as compared to the cell. In this case, the cell has less salts and more water as compared to outside the cell. Osmosis dictates that water will move from higher to lower concentration out of the cell. This is known as plasmolysis of the bacteria; the cells are called plasmolyzed. The high salt content depresses the growth of the other genera, but enriches for the Staphylococci.
This is how we can preserve food and protect the skin's flora, because Staph grows naturally and without recourse normally on the skin

hypotonic solution means that it has a low concentration of solutes and higher concentration of water as compared to the cell. Osmosis would occur from higher to lower concentration into the cell and the cytoplasm would fill up with water. Prokaryotic cells won't burst because of the presence of the cell wall; this is also true of plants which also have a cell wall. The cytoplasm will fill up and press upon the cell membrane. We call the pressure that builds up because of the force of the water moving into the cell turgor pressure; these cells are said to be turgid.