Their optimum growth temperature is between 45C and 70C and are comonly found in hot springs and in compost heaps. Hyperthermophiles are bacteria that grow at very high temperatures. They are usually members of the Archae and are found growing near hydrothermal vents at great depths in the ocean. A colony is a visible mass of microorganisms growing on an agar surface and usually originating from a single organism or arrangement of organisms. Single colonies can be described using standard terms, as listed in Appendix A .
Some microorganisms produce pigment during growth and are said to be chromogenic .
Often, however, formation of pigment depends on environmental factors such as temperature, nutrients, pH and moisture. If the pigment is water insoluble , as in the case of most chromogenic bacteria, it does not diffuse out of the organism. As a result, the colonies are pigmented but the agar remains the normal color. Both the colonies and the agar will appear pigmented. Aseptically inoculate one Trypticase Soy Broth tube with B. subtilis , one with E. coli , one with M. luteus , and one with M. phlei .