Groups of Firmicutes have been classified based on characteristics like type of cell envelope, endospore formation and aerotolerance (how well they live and grow in oxygen). Currently, there are three recognized Classes of Firmicutes: the Mollicutes, the Clostridia and the Bacilli.
Mollicutes such as the Mycoplasma are very small cells lacking a peptidoglycan cell wall. Without a cell wall these bacteria tend to be very delicate. Therefore Mollicutes are often closely associated with a host that can provide them with a stable environment. They also have special lipids called sterols and lipoglycans, to help protect against osmotic stress. This group contains several very important human pathogens that can cause pneumonia, urethritis, carditis, and gingivitis, to name a few.
What does Low G+C mean?
The DNA of all living things is made up of four nucleotide bases Adenine (A), Cytosine (C), Guanine (G) and Thymidine (T). In a double helix of DNA, Adenine pairs with Thymidine and Guanine pairs with Cytosine. Therefore the number of Cytosine bases equals the number of Guanine bases and likewise A=T. The percentage of G+C is one of many general features used to characterize bacterial genomes.
