Chapter 7 Microbial Growth Binary fission Steps in Binary Fission ...

Obligate aerobe• Requires oxygen for metabolism• Possess enzymes that can neutralizethe toxic oxygen metabolites– Superoxide dismutase andcatalase• Ex. Most fungi, protozoa, andbacteriaFacultative anaerobe• Does not require oxygen formetabolism, but can grow in its presence• During oxygen limitation states, anaerobicrespiration or fermentation occurs• Possess superoxide dismutase andcatalase• Ex. Gram negative pathogensObligate anaerobes• Cannot use oxygen for metabolism• Do not possess superoxide dismutaseand catalase• The presence of oxygen is toxic to thecell• Ex - dental pathogens, intestinalpathogens, deep in tissuespHpH - negative logarithm of thehydrogen ion concentration of anaqueous solution• Most cells grow best between pH 6 - 8• Exceptions would be acidophiles (pH 0)and alkalinophiles (pH 10).Osmotic pressure• Halophiles• Require high salt concentrations• Withstand hypertonic conditions• Ex. Halobacterium• Facultative halophiles– Can survive high salt conditions but isnot required– Ex. Staphylococcus aureusOther factors?• Barophiles – withstand highpressures• Spores and cysts- can survive dryhabitats5