What are the different types of aerobes?

Aerobes are organisms that can only live and reproduce in the presence of free oxygen. There are four types of aerobes – obligate aerobes, facultative aerobes, microaerophiles, and aerotolerant aerobes. 

Obligate aerobes

Obligate aerobes are aerobes that cannot survive without oxygen. The presence of oxygen in the environment is mandatory for their survival and growth. 

Examples of obligate aerobes: Mycobacterium, Bacillus 

Facultative aerobes

Facultative aerobes do not depend on the presence of oxygen in their environment for survival and growth. They can grow in the absence and presence of oxygen. These aerobes produce ATP molecules using anaerobic processes, and can hence live and grow even in the absence of oxygen. 

Example of facultative aerobes: Enterobacteriaceae

Microaerophiles

Microaerophiles need oxygen for survival and growth but cannot survive the higher levels of oxygen present in the atmosphere. The higher atmospheric concentrations of oxygen can be lethal to these aerobes. Microaerophiles require only a small amount of oxygen to generate energy. These organisms do not have an electron transport system. They depend on the fermentation reaction for energy generation. 

Examples of microaerophiles: Campylobacter, Helicobacter

Aerotolerant anaerobes

Aerotoleratant anaerobes do not use oxygen for energy generation nor for any metabolic activity. They do not possess enzymes that are necessary for aerobic respiration. However, the presence of oxygen in the environment does not adversely affect them either. 

Examples of aerotolerant anaerobes: Streptococci, Lactobacilli