Aerobic capsulated bacteria

Aerobic capsulated bacteria such as Aerobacter, Flavobacterium and Pseudomonas are generally associated with slime problems. Bacterial cell walls are composed of amino acids, polysaccharides and lipids, while the interior of the cell is composed of the nucleoprotein, dispersed in the "soup-like" cytoplasm. The outside slime layer of these organisms is composed of polysaccharides and polypeptides. These serve to protect the cell from the environment, increase its ability to catch food entangled in its sticky mass and may be redigested by the organism when food is lacking.

Organisms such as Bacillus mycoides, Bacillus subtilis and other aerobic spore formers produce slimes to a lesser extent than do the aerobic capsulated organisms. They are worthy of note, however, because of their capacity to form spores, which cause the control problems previously mentioned.

Aerobic sulfur bacteria, notably the Thiobacillus, can oxidize sulfur and sulfides to sulfates or sulfuric acid. In local areas, they have been known to produce up to ten percent sulfuric acid, while dropping the pH to as low as 1.0. Often the presence of aerobic bacteria complements colonies of anaerobic bacteria which may be present beneath them. 

This symbiotic relationship exists where anaerobic sulfate-reducing bacteria are underneath aerobic sulfur bacteria deposits. Sulfate-reducing bacteria, such as Desulfovibrio desulfuricans, are capable of reducing sulfates to hydrogen sulfide. 

Since the sulfate ion is found in almost all industrial water systems, the potential danger posed by sulfate-reducing bacteria is quite real. The presence of these species is identified by black iron sulfide deposits.

Iron bacteria such as Crenothrix, Sphaerotilus and Gallionella utilize iron for their growth and secrete iron deposits as a byproduct of their metabolism.

To generate energy requisite for their growth, they must produce large quantities of ferric hydroxide. The iron produced becomes entwined in the organism producing a voluminous deposit which causes plugging, pitting corrosion and reduced heat transfer. These organisms are commonly found in well casings or iron-bearing aquifers. They may enter a industrial tower if water from these sources is used as makeup. In other situations the organisms may manifest themselves inside the system.