Group VII – Acetic Acid Bacteria
Examples of these include the genera:
• Acetobacter
• Gluconobacter
These are gram negative, motile, aerobic rods. They convert ethanol to acetic acid (น้ำส้มสายชู). That can be a good thing if your goal is to make acetic acid. However, these organisms are known for spoiling alcoholic beverages (wine). That is a bad thing.
They grow well at ph < 5. This is to be expected of an acid producer.
They also produce sorbose from sorbitol in a process known as biotransformation. Sorbose is a precursor for the manufacture of ascorbic acid (Vitamin C). It is difficult to obtain sorbose by other means.
Acetic acid bacteria are also unusual that they can produce external cellulose. They encase themselves in cellulose to form a pellicle that floats on the surface of wine. In this way, they stay in aerobic conditions.
Group VIII – Free Living Aerobic Nitrogen Fixing Bacteria
These are bacteria that have the ability to convert molecular nitrogen (N2) to other compounds when growing on an organic substrate. Although they have the ability to fix nitrogen, they can use other nitrogen sources as well, such as ammonia, nitrate and urea.
There is another group of microorganism that fix nitrogen, but they are associated with plant roots. They are not free living.
They are commonly pleomorphic (can change shape).
Common genera include:
• Azotobacer
• Azomonas
• Azospirillum