Final answer:
Bacteria are primarily classified into two groups: Gram-positive, which stain purple and have a thick cell wall, and Gram-negative, which stain pink/red and have an outer membrane. Further classification includes deeply branching bacteria and subdivisions within Gram-negative bacteria, like Proteobacteria.
Step-by-step explanation:
Classifications of Bacteria
The two main classifications of bacteria are Gram-positive and Gram-negative bacteria. This classification is based on the differences in their cell walls and outer membranes, which can be observed by their reaction to the Gram stain.
Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, staining purple, and generally lack an outer membrane.
In contrast, Gram-negative bacteria have a thinner layer of peptidoglycan and an additional outer membrane, staining pink or red.
Further classifications include the deeply branching bacteria and the divisions within Gram-negative bacteria such as Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB), and spirochetes.
Proteobacteria are subdivided further from Alpha- to Epsilon classes. Eukaryotic mitochondria and chloroplasts are thought to have evolved from alphaproteobacteria and cyanobacteria respectively.
Bacteria are incredibly diverse and abundant and are found in nearly every habitat including the human body. While some bacteria are pathogenic, most are benign or beneficial to humans.
Scientists constantly work to classify these prokaryotes more accurately as new discoveries are made.