They include elements such as carbon (C), oxygen (0) and hydrogen (H) constituting organic compounds like carbohydrates. Nitrogen (N) is found in microbial cells in proteins, nucleic acids and coenzyrnes. Sulfur (S) is needed for S-containing amino acids such as methionine and cysteine and for various coenzymes. Phosphorus (P) is present in nucleic acids, phospholipids, teichoic acid and nucleotides including NAD(P) and ATP. Potassium is the major inor- ganic cation (K+), while chloride (C1‘) is the major inorganic anion. K+ is required as a cofactor for certain enzymes, e.g. pyruvate kinase. Chloride is involved in the energy conservation process operated by halophilic archaea (Section 11.6). Sodium (Na+) participates in sev- eral transport and energy transduction processes, and plays a crucial role in rnicrobial growth under alkaline conditions (Section 5.7.4). Magnesium (Mg2+) forms complexes with phosphate groups including those found in nucleic acids, ATP, phospholipids and 1ipopolysacchar- ides. Several microbial intracellular enzymes, e. g. monomeric alkaline Phosphatase, are calcium dependent. Ferrous and ferric ions play a