Organic acid-forming bacteria

Organic Acid-Forming Bacteria 4.1 Acetic Acid (C2)... 

Volatile organic acids are not toxic to methane bacteria at concentrations up to 6000 mg/liter. Propionic acid is slightly toxic at this level to acid-forming bacteria. Thus, pH control with alkaline substances during unbalanced digestion is a valid procedure. However, care must be exercised that the cation of the alkaline material does not produce a toxic condition. 

The proportion of acid-forming bacteria in plaque samples from caries-active individuals is greater than in samples from caries-inactive individuals (Table 36.2). This ratio of acidogenic to total plaque organisms is significantly increased by supplementing the diet with sucrose. 

Thiobacillus thiooxidans is an aerobic organism that oxidizes various sulfur-containing compounds to form sulfuric acid. These bacteria are sometimes found near the tops of tubercles (see Chap. 3, Tubercu-lation ). There is a symbiotic relationship between Thiobacillus and sulfate reducers Thiobacillus oxidizes sulfide to sulfate, whereas the sulfate reducers convert sulfide to sulfate. It is unclear to what extent Thiobacillus directly influences corrosion processes inside tubercles. It is more likely that they indirectly increase corrosion by accelerating sulfate-reducer activity deep in the tubercles. 

Short-chain and low molecular weight organic acids, such as acetic acid and formic acid, can be formed by certain bacteria. The resulting organic acid salts are not easily detected without specialized analytical equipment in a laboratory. 

Human use of acids and bases dates back thousands of years. Probably the first acid to be produced in large quantities was acetic acid, HC HjO. Vinegar is a diluted aqueous solution of acetic acid. This acid is an organic acid that forms when naturally occurring bacteria called acetobacter aceti convert alcohol to acetic acid. Ancient Sumerians used wine to produce vinegar for... 

Nitrous acid, formed from organic precursors such as nitrosamines and from nitrite and nitrate salts, is a potent accelerator of the deamination of bases. Bisulfite has similar effects. Both agents are used as preservatives in processed foods to prevent the growth of toxic bacteria. They do not appear to increase cancer risks... 

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