Eubacteria and Archaebacteria

Archaebacteria are the oldest living organisms on earth. They are prokaryotes and unicellular. Archaebacteria are found in very harsh conditions (such as at the bottom of the sea or in volcanic vents). This is thought to be because the early Earth’s atmosphere was filled with poisonous gases and was very hot – nothing could survive, except the archaebacteria. These slowly gave way to modern organisms when the Earth’s conditions settled down and oxygen was introduced to the atmosphere. There are three phyla, or groups, of archaebacteria. methanogens (harvest energy into methane), halophiles (extreme salt conditions) and thermoacidophiles (extreme temperature conditions).

The eubacteria are more complex, and common, than the archaebacteria. It is the eubacteria that most people are talking about when they say bacteria, because they live in more neutral conditions. They can be found everywhere around us – in our bodies, our food, etc. There are four phyla of bacteria, some of which are divided into subgroups. Cyanobacteria are photosynthetic, like plants. Spirochetes are gram-negative, and heterotrophic (also pathogenic). Gram-positive bacteria can be pathogenic (heterotrophic). Proteobacteria is one of the largest phyla of all the bacteria. Many are gram-negative.