Cell walls, present in some forms, are composed of cellulose . When present, flagella contain microtubules. Structural diversity is substantial, but metabolic diversity is fairly limited. They are similar to one another with respect to metabolic pathways. Some of these processes involve the plasmid , a circular molecule of DNA which is present outside of the nucleoid of some forms of bacteria.
Mutation is very important in the evolution and adaptation in asexually reproducing organisms.
It results in such phenomena as antibiotic resistance. Another phenomenon is noteworthy. Many bacteria can produce a resistant structure called a bacterial endospore . Endospore germination may occur after as many as 1,000 years of dormancy . Classification of Bacteria Most bacterial classification schemes are artificial and are constantly in a state of flux.