19 Apr

pH and Microbial Growth

It is important to understand the relationship between pH and microbial growth. The pH or hydrogen ion concentration affects proteins and other charged molecules in the cell. Each organism has an optimal pH at which point they grow best. If the pH value exceeds the optimal pH the solubility of charged molecules can be adversely affected and molecules can precipitate out of solution. The pH can alter the charge on amino acids and result in denaturation of the protein. Like temperature, microorganisms can be subdivided into groups based on their ability to grow at different ph values. Bacteria that can grow at or near neutral pH are classified as neutrophiles. Most bacteria are neutrophiles although many can grow over a range of 2-3 pH units. Bacteria that grow at acidic pH values are acidophiles and bacteria that grow at alkaline pH values are termed alkaliphiles. Thiobacillus thiooxidans can grow at pH 1 and it derives its envergy needs from the oxidation of sulfide. They then produce sulfuric acid that lowers the pH of the environment. True alkalinophilic bacteria can be found growing in environments such as high carbonate soils where the ph is 10 or above.