CLASSIFICATION OF BACTERIA and BACTERIAL POPULATION

• Bacteria can be classified based on their source of energy and carbon.
• Chemoheterotrophs oxidize organic compounds for energy and carbon.
• Chemoautotrophs oxidize inorganic substances such as ammonia, sulfides and ferrous compounds for energy and carbon.
• Photoheterotrophs use light as an energy source and organic compounds as a carbon source.
• Chloroflexus, Heliobacterium, Heliothrix, and Rhodocyclus are examples of photoheterotrophs.
• Chlorobium, Chloroherpeton, Chromatium, Pelodictyon, and Thiodictyon are examples of photosynthetic bacteria.
• Psychrophiles grow well at 0C and have an optimum growth temperature of 15C or lower, with a maximum around 20C.
• Psychrotrophs are species of bacteria that can grow at 0C even though they have optima between 20 and 30C, and a maxima at about 35C.
• Psychrotrophic bacteria and fungi are major factors in the spoilage of refrigerated foods.
• Mesophiles are microorganisms with growth optima around 20 to 45C and a temperature minimum of 15 to 20C.
• Most microorganisms probably fall within the mesophile category.
• Almost all human pathogens are mesophiles, as might be expected since their environment is fairly constant at 37C.
• Some microorganisms are thermophiles; they can grow at temperatures of 55C or higher, with a growth minimum usually around 45C and often having optima between 55 and 65C.
• Bacteria that have growth optima between 80C and about 110C are called hyperthermophiles, which usually do not grow well below 55C.
• Aerobe is an organism able to grow in the presence of atmospheric oxygen.
• Anaerobe is an organism that can grow in the absence of oxygen.
• Facultative anaerobes do not require oxygen for growth but do grow better in its presence.
• Aerotolerant anaerobes ignore oxygen and grow equally well whether it is present or not.
• Strict or obligate anaerobes do not tolerate oxygen at all and die in its presence.
• Microaerophiles cannot tolerate atmospheric oxygen and require oxygen levels below the range of 2% to 10% for growth.
• Acidophiles have their growth optimum between pH 0 to 5.5.
• Neutrophiles have their growth optimum between pH 5.5 to 8.0.
• Alkalophiles prefer the pH range of 8.5 to 11.5.
• The first phase of the growth curve is the lag phase during which the bacteria absorb nutrients, synthesize enzymes, and prepare for cell division.
• The second phase of the growth curve is the logarithmic phase (also known as log phase or exponential growth phase) in which the bacteria multiply so rapidly that the number of organisms doubles with each generation time.
• Growth rate is the greatest during log phase.