16 Dec

pH and Growth

It is important to understand the relationship between pH and growth of microorganisms. Cells can be greatly effected by changes in pH. Proteins maintain a specific charge based on the pH of the surrounding solution. If the pH changes, the charge on the amino acid changes which will cause a change in the overall structure and function of the protein. Microorganisms can be divided into groups based on their ability to function at different pH values. Bacteria that grow at or near neutral pH are classified as neutrophiles. Most bacteria are neutrophiles however most bacteria can grow over a range of 2-3 pH units. Bacteria that grow at acidic pH values are acidophiles. The chemolithotroph Thiobacillus thioxidans is an acidophile that grows at pH of 1. It can be found in mining effluents that are enriched in metal sulfide ores. Bacteria that grow at alkaline pH values are termed alkaliphiles. True alkalinophilic bacteria are found growing in environments such as soda lakes and high carbonate soils where the pH can reach 10 or above. The majority of these bacteria belong to the species bacillus. Because pH can influence the growth of an organism, it is used in food preservation. As foods ferment they produce lactic acid which lowers the pH of the surrounding environment preventing other microorganisms to grow.