Classification of Bacteria

OBLIGATE AEROBES: Requires O2 for Growth
OBLIGATE ANAEROBES: Do not required O2. E.g. Clostridium species.
FACULTATIVE AEROBES: Mainly anaerobes
FACULTATIVE ANAEROBES: Mainly aerobes (E.coli, clostridium sporogenes)
MICROAEROPHILE: Require very low concentration of oxygen.

Anaerobes have absence of 3 enzymes which are present in aerobes.
(i) Superoxide demutase: Eliminate Superoxide radical.
(ii) Catalase: Breakdown of H2O2 H2O + O2
(iii) Peroxidase: H2O2 + Reduced substance H2O + Oxidised substance

So free radicals produced in anaerobes in O2 environment. So anaerobes dies.
* Optimum pH for bacterial growth is 6.5-7.5.
* Bacteria can not tolerate salt but fungi tolerates salt.

Psychrophiles: Below 25 degree C (vibrio species)
Mesophiles: 25-45 degree C
Thermophiles: Optimum 55-65 degree C. Thermophilus.
Acidophilic: Tolerate high acidic condition (Lactobacilli)
Basophilic: Tolerate Alkaline condition (Vibrio cholerae)