Chemical requirements for bacterial growth

Carbon

energy source

• like humans, bacteria are made primarily of carbon based organic molecules

chemoheterotroph

an organism that obtains both its energy and its carbon by consuming pre-existing organic compounds

• use organic carbon sources (cannot use carbon directly to make their own organic compounds)

Autotrophs

use CO2 (synthesize their own organic molecules)

Nitrogen

• in amino acids, proteins; nucleic acids

• some bacteria use NH4+ or NO3- for energy

• a few use N2 in nitrogen fixation

Most bacteria decompose

proteins

Sulfur

• In amino acids (cys and met), thiamine, biotin

• Some bacteria use SO42 or H2S for energy

Phosphorus

• In DNA, RNA, ATP, and membranes

• PO43 is a source of phosphorus

Obligate aerobes

require oxygen

• sit at the top of a culture broth tube

Facultative anaerobe

prefer oxygen but can grow without it

• mostly at the top of the culture broth tube but also suspended throughout

Obligate anaerobes

find oxygen toxic

• it can cause cell death

• found at the bottom of the culture broth tube

aerotolerant anaerobes

don’t need oxygen to grow but it won’t harm them

• found suspended throughout the entire culture broth tube

microaerophiles

grow only when oxygen is present at a very specific quantity or in a very small amount

Toxic forms of oxygen

• singlet oxygen

• superoxide free radicals

• peroxide anion

• hydroxyl radical

Superoxide dismutase (SOD)

converts superoxide free radicals (which are very unstable and highly reactive) to molecular oxygen and peroxide (which is toxic by itself)

O2 - + 2H+ —→ H2O2 + O2

Catalase

enzyme organisms use to detoxify peroxide which generates oxygen and water from peroxide

2H2O2 —→ 2H2O + O2

Peroxidase follows:

H2O2 + 2O+ —→ 2H2O