Bacteria can be classified in several ways: 1. Based on their morphology, bacteria are grouped as cocci, bacilli, spirilla, etc. depending on whether they are spherical, rod-shaped, spiral-shaped. 2. Bacteria are also classified based on their metabolic activities - whether they require oxygen (aerobic), do not require oxygen (anaerobic), or can survive in extreme conditions. 3. DNA sequencing and cell structure such as cell wall contents, presence of flagella, and formation of endospores are other factors used to classify bacteria into different phyla and groups.