Classification Of Bacteria

Classification of Bacteria Asad Naz

On the basis of availability of temperature, pH, nutrition and oxygen, bacteria are divided into different categories.

Temperature 1. Psychrophiles -- cold loving microbes 2. Mesophiles --moderate-temperature loving organism -- most pathogens and indigenous flora 3. Thermophiles -- heat loving microbes -- ex. Thermophilic cyanobacteria found in hot springs -- Thermodurics: organisms that can survive endure boiling--- ex. Endospores and viruses

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contd.. GROWTH TEMPERATURES: 1. Minimum Growth temperature - lowest temperature at which the species will grow 2. Optimum Growth temperature - temperature at which the species grows best 3. Maximum Growth temperature - highest temperature at which growth is possible

Contd.. Table 1. Temperature ranges for different bacteria. Classification Temperature Range (°C) Optimum Growth Temperature (°C) Psychrophile Psychrotroph Mesophile Thermophile Hyperthermophile

-10 to 20 5 to 30 10 to 45 40 to 75 65 to 120

10 25 37 55 90-100

pH Acidity or alkalinity of a solution 1. Neutrophiles -- neutral growth medium (pH 7) -- most microorganisms 2. Acidophiles --prefer a pH of 2-5 --microbes that can live in the stomach 3. Alkaliphiles (Basophiles) --prefer pH greater 8.5 -- found in intestine

Oxygen requirement -Based on relationship to O2 1. Aerobes---use molecular O2 for life and reproduction a. Obligate aerobes - require an atmosphere that contains O2 similar to room air (20-21% O2), Ex. Mycobacteria b. Microaerophiles - require O2 lower than room air (=5% O2) - ex. Neisseria, Campylobacter 2. Anaerobes - do not require O2 for life and reproduction - vary based on sensitivity to O2 a. Obligate anaerobe - unable to grow in O2, ex. Clostridium

Contd.. b. Facultative anaerobe - capable of surviving in the presence or absence of O2 (0% to 20-21% O2) - ex. Enterobacteria, streptococci, staphylococci c. Aerotolerant anaerobe - does not require O2 - grows better in the absence of oxygen but can survive in atmosphere containing O2 - ex. Lactobacilli - Based on relationship to CO2 - Capnophiles– grow better in the presence of increased concentrations of CO2 - Anaerobes– Bacteroides, Fusobacterium - Aerobes– Neisseria,Campylobacter, Hemophilus

Nutrition Requirement 

Source of Energy

--Phototrophs---light --Chemotrophs– inorganic or organic compounds

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Source of Carbon

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Autotrophs---CO2 Litotrophs—inorganic compound except CO2 Heterotrophs (Organotrophs) ---Organic compounds

Energy Source and Carbon Source

--Photoautotrophs---Light + CO2 ---ex. Plants, algae, cyanobacteria, purple and green sulfur bacteria --Photoheterotrophs (Photoorganotrophs) --- Light + organic compounds—ex. Green and purple non-sulfur bacteria

Contd.. --Chemoautotrophs– Chemical + CO2 ex. Nitrifying, hydrogen, iron and sulfur bacteria --Chemolitotrophs--- Chemical + inorganic compound except CO2 -- Chemoheterotrophs– Chemical + organic compound ex. All animals, protozoa, fungi, most bacteria -- Photolithotrophs – Light + inorganic compound except CO2 ex. Plants and algae: producers of food and O2 for chemoheterotrophs

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