Microbes have different oxygen requirements. Bacteria like Micrococcus and Sarcina found in the soil and air require oxygen for growth and are called aerobes. Some microbes including E.coli do not require oxygen but grow better when oxygen is present. Micro-aerophilic microbes in water require low levels of oxygen for best growth. Methanobacterium and Clostridium are anaerobes and do not grow if oxygen is present; still other microbes like Streptococcus in the upper breathing structures grow with or without oxygen. Increasing the levels of carbon dioxide to 3-10% will increase the growth of capnophiles like Neisseria, Brucella, and Streptococcus pneumoniae.

Microbe growth is also influenced by the pH of the environment. A pH change of one indicates a 10-fold change in hydrogen ion concentration, so vinegar with a pH of 2 and household bleach with a pH of 11 differ by a billionfold in hydrogen ion concentration. Microbes that grow best in low pH (acids) like vinegar are called acidophiles. When acidophiles like Thiobacillus are placed in environments that are not acidic, the cell membrane is destroyed. Numerous fungi grow well in acidic surroundings. A few microbes grow well at high pH (pH of 8-11); and these alkalophiles include some aerobic species of Bacillus in high pH soils. Most microbes grow best at a neutral pH around 7; and these common microbes are called neutrophiles.