Difference Between

Bacteria vs Archaea
 

Organisms can be classified into 3 domains. Those are eukarya, bacteria and archaea.

Bacteria

Bacteria were first observed in 1674. The name originated from the Greek word “small stick”. They are unicellular and typically few micrometers long. They have a diversity of shapes. They may occur attach to surfaces. They form biofilms having different species. Thickness can be a few micrometers to several centimeters. There are many shapes such as cocoid, bacilli, spiral, comma and filamentous. There is no membrane bound organelles. They lack a nucleus, mitochondria, chloroplasts, golgibodies and ER. DNA is present in the cytoplasm, in an area called nucleoid. DNA is highly coiled. 70s type ribosomes are present. Cell wall consists of peptidoglycans. Gram positive bacteria possess a thick cell wall with several layers of peptidoglycan. Gram negative bacteria cell wall has few layers surrounded by a lipid layer. A smaller DNA molecule may also be present. It is called a plasmid.

The plasmid is circular and contains extra chromosomal material. It undergoes self replication. They carry genetic information. However, the plasmid is not essential for the survival of the cell. Flagella are rigis protein structures used in motility. Fimbriae are fine filaments of protein involved in attachment. Slime layer is a disorganized layer of extra cellular polymers. Capsule is a rigid polysaccharide structure. It is also called the glycocalyx. The capsule provides protection. It contains polypeptides. Hence it resists phagocytosis. Capsule is involved in recognition, adherence and formation of biofilms. Capsule is associated with the pathogenesis. Some produce endospores, which are highly resistant dormant structures.

Archaea

Archaea are a fascinating group of organisms. They were discovered in the 1970’s, and they were considered as a part of bacteria. They are referred to as archaebacteria. Recent work has shown that there are distinct differences between bacteria and archaea. Hence they are called archaea and not archaebacteria. Archaea represent the most primitive organisms yet discovered. Archaea are unique for 2 reasons. Firstly, they represent the most primitive organisms yet discovered. They resemble the early fossils dated 2 million years old. Secondly archaea live in very extreme environments and are referred to as extremophiles. Their habitats include hot springs, rift vents in the deep sea, hyper saline water, petroleum deposits, digestive tracts of cows, termites and marine life.

Archaea are tiny organisms, which are less than 1 micron long. Archaea have a variety of shapes such as coccoid, bacilli and other odd shapes. 3 major groups are recognized based on their physiology. They are methanogens, extreme thermophiles and extreme halophiles. Methanogens are anaerobes. They live at the bottom of ponds, sewage lagoons and intestinal tracts of animals. They use hydrogen compounds and carbon dioxide to produce energy. In this process, they release methane. Extreme thermophiles live in extremely hot waters such as geysers, hot vents on the ocean floor etc. They oxidize sulfur to obtain energy. Sulphuric acid is released as a waste product. Extreme halophiles live in high salt water such as in Dead Sea.