Sec 2: Nutrition of Microorganisms

Nutrition of Microorganisms Cells consist mainly of macromolecules and water.Macromolecules are polymers of the smallest units called monomers. Microorganism nutrition is one aspect of the physiology of microorganisms which, among other things, studies the use of monomers needed for cell growth. The substances needed are called nutrients. Different microorganisms require different sets of nutrients and not all required nutrients are present in the same amounts. Nutrients that are classified as macronutrients are needed in large quantities while those that are small are called micronutrients. All cells need carbon and most prokaryotes need organic compounds as a carbon source. Carbon covers 50% of the dry weight of cells and carbon is the main element in macromolecules. Bacteria can assimilate various sources of organic C and use them to form cellular materials. Amino acids, fatty acids, organic acids, sugars, nitrogen bases, aromatic compounds, and many other organic compounds can be used. Some prokaryotes are autotrophs, able to form cellular structures from carbon dioxide with energy from light or other inorganic compounds. Apart from carbon, the element that is needed most is nitrogen. Bacterial cells contain 12% nitrogen in cell dry weight. Nitrogen is important for proteins, nucleic acids and cell building blocks. In nature, nitrogen is available in inorganic and organic forms, but mostly in inorganic forms such as NH3, NO3, N2. Most bacteria can use ammonia as a source of nitrogen or nitrate, while nitrogen gas is needed by certain bacteria which are classified as N2 fixers. Phosphorus in nature exists in organic and inorganic forms and is indispensable for the synthesis of nucleic acids and phospholipids. Sulfur is needed for the structure of the amino acids cysteine and methionine, and is also found in several vitamins such as thiamine, biotin, lipoic acid and coenzymes. Sulfur is available to microorganisms in various forms and undergoes mediated by microorganisms. Sulfur in cells comes from inorganic sources such as sulfate (SO4 2-), and sulfide (HS- ). Potassium is needed by all organisms. Various enzymes involved in protein synthesis require potassium for their activity. Magnesium functions to stabilize ribosomes, membranes and nucleic acids, and enzymes are also needed for their activity. Calcium is not an essential element for the growth of microorganisms but can stabilize cell walls and play a role in endospore stability. Sodium is needed by certain organisms and is used as an indicator of their habitat, for example sea water contains high sodium and marine microorganisms need sodium for growth while freshwater microorganisms do not need it. Iron plays an important role in cellular respiration and is a key component of cytochromes and Fe-S proteins involved in electron transport. In anoxic environments, Fe is in the easily soluble Fe2+ form, while in oxic environments it is in the insoluble Fe3+ form. To obtain iron from minerals, cells produce siderophores that bind iron and transport it into the cell. One group of siderophores consists of hydroxamic acid derivatives that strongly chelate iron. After the Fe-hydroxamate complex enters the cell, iron is released and the hydroxamate is excreted to re-transport Fe. Escherichia coli and Salmonella typhimurium produces the phenolic siderophore enterobactin. This siderophore is a derivative of the aromatic compound catechol which has a high affinity for Fe. Without Fe-binding agents, pathogens cannot initiate infection. Iron is little found in animal tissue because Fe is quickly bound and is not available to microorganisms. Little iron is detected in the marine environment, only a few picograms (1 picogram: 10-12 g) per ml. To overcome this, marine bacteria produce siderophores which can take up iron, even in small amounts. This siderophore has a peptide head that forms a complex with Fe3+ and a lipid tail that is associated with the cytoplasmic membrane. This compound, aquakeline, binds iron and forms aggregates into lipid-like However, some prokaryotes can survive without iron, for example Lactobacillus plantarum and Borelia burgdorferii (which causes Lyme disease). As a substitute for iron, Mn2+ is a component of metal-containing enzymes (metalloenzymes). Micronutrients play an important role in carrying out cell functions. Micronutrients, such as iron metal, are needed in small quantities and are often called trace elements which act as components of various enzymes. For routine laboratory needs, trace elements are often not added because the amounts are too small. If the media components are very pure and distilled also pure, micronutrient deficiencies often occur. In this case dilute trace elements can be added to meet the need for the element the. Micronutrients needed by living organisms             Boron (B) : Quorum sensing autoinducer, polyketide antibiotic Chromium (Cr) : Glucose metabolism in mammals Cobalt (Co) : Vitamin B12, transcarboxylase (propionic acid bacteria) Copper (Cu) : Respiration, cytochrome c oxidation, photosynthesis, plastocyanin, some superoxide dismutases Iron (Fe) : Cytochrome, catalase,peroxidase, iron-sulfur protein, oxygenase, nitrogenase Manganese (Mn) : Activator of the superoxide dismutase enzyme, a water-splitting enzyme in oxygenic phototrophs Molybdenum (Mo) : Flavin enzyme, nitrogenase, nitrate reductase, sulfur oxidase, DMSO-TMAO reductase, multiple formate dehydrogenase Nickel (Ni) : Hydrogenase, coenzyme F430, methanogen, carbon monoxide dehydrogenase, urease Selenium (Se) : sour dehydrogenase, amino, Formate hydrogenase, selenocysteine Wolfram (W) : dehydrogenase, Hyperthermophilic oxotransferase formate Vanadium (V) : V-nitrogenase, bromoperoxidase Zinc (Zn) : Carbonic anhydrase, alcohol dehydrogenase, RNA, and DNA polymerase, DNA binding proteins.