Acidophiles live at low pH Obligate acidophiles such as Thiobacillus. Important to biotechnology since they have hydolytic proteases that function at alkaline pH and are used in household cleaners. Water availability - bacteria need water as a solvent. Water availability is expressed as water activity - how much water is available. Water moves from high water activity values to lower values in the process of osmosis .
Different bacteria have different tolerances towards low water activities.
In fact, preservation process takes advantage of lower water activity which causes plasmolysis or pulling away of the membrane from the cell wall. This inhibits cell growth. Oxygen - 1. Microaerophilic bacteria require reduced levels of oxygen 3. Facultative anaerobes can grow aerobically if oxygen is present and switch to fermentation or anaerobic respiration if oxygen is absent.