128 Fermentation and Biochemical Engineering Handbook The predominant atomic constituents of organisms, C,H,N, O S, go into making up the molecules of living matter. All living cells on earth contain water as their predominant constituent. The remainder of the cell consists largely of proteins, nucleic acids, lipids, and carbohydrates, along with a few common salts. A few smaller compounds are very ubiquitous and function universally in bioenergetics, e.g., ATP for energy capture and transfer, and NAD in biochemical dehydrogenation. Microorganisms share similar chemical compositions and universal pathways. They all have to accomplish energy transfer and conversion, as well as synthesis of specific and patterned chemical structures [1 The microbial environment is largely determined by the composition of the growth medium. Using pure compounds in precisely defined proportions yields a defined or synthetic medium. This is usually preferred for research- ing specific requirements for growth and product formation by systematically adding or eliminating chemical species from the formulation. Defined medi can be easily reproduced, have low foaming tendency, show translucency and allow easy product recovery and purification Complex or natural media such as molasses, corm steep liquor, meat extracts, etc, are not completely defined chemically, however, they are the media of choice in industrial fermentations In many cases the complex or natural media have to be supplemented with mainly inorganic nutrients to satisfy the requirements of the fermenting organism. The objective in media formulation is to blend ingredients rich some nutrients and deficient in others with materials possessing other profiles to achieve the proper chemical balance at the lowest cost and still allow easy processing 4I Fermentation nutrients are generally classified as: sources of carbon, nitrogen and sulfur, minerals and vitamins 3.0 THE CARBON SOURCE Biomass is typically 50% carbon on a dry weight basis, an indication of how important it is. Since organic substances are at the same general oxidation level as organic cell constituents, they do not have to undergo a primary reduction to serve as sources of cell carbon. They also serve as an energy source. Consequently, much of this carbon enters the pathways of energy-yielding metabolism and is eventually secreted from the cell as Co (the major product of energy-yielding respiratory metabolism or as a mixture of cO2 and organic compounds, the typical end-products of fermentation metabolism). Many microorganisms can use a single organic compound to128 Fermentation and Biochemical Engineering Handbook The predominant atomic constituents of organisms, C, H, N, 0, P, and S, go into making up the molecules of living matter. All living cells on earth contain water as their predominant constituent. The remainder of the cell consists largely of proteins, nucleic acids, lipids, and carbohydrates, along with a few common salts. A few smaller compounds are very ubiquitous and function universally in bioenergetics, e.g., ATP for energy capture and transfer, and NAD in biochemical dehydrogenation. Microorganisms share similar chemical compositions and universal pathways. They all have to accomplish energy transfer and conversion, as well as synthesis of specific and patterned chemical structures.['] The microbial environment is largely determined by the composition of the growth medium. Using pure compounds in precisely defined proportions yields a defined or synthetic medium. This is usually preferred for research￾ing specific requirements for growth and product formation by systematically adding or eliminating chemical species from the formulation. Defined media can be easily reproduced, have low foaming tendency, show translucency and allow easy product recovery and purification. Complex or natural media such as molasses, corn steep liquor, meat extracts, etc., are not completely defined chemically, however, they are the media of choice in industrial fermentations. In many cases the complex or natural media have to be supplemented with mainly inorganic nutrients to satisfy the requirements of the fermenting organism. The objective in media formulation is to blend ingredients rich in some nutrients and deficient in others with materials possessing other profiles to achieve the proper chemical balance at the lowest cost and still allow easy processing.r4I Fermentation nutrients are generally classified as: sources of carbon, nitrogen and sulfbr, minerals and vitamins. 3.0 THE CARBON SOURCE Biomass is typically 50% carbon on a dry weight basis, an indication of how important it is. Since organic substances are at the same general oxidation level as organic cell constituents, they do not have to undergo a primary reduction to serve as sources of cell carbon. They also serve as an energy source. Consequently, much of this carbon enters the pathways of energy-yielding metabolism and is eventually secreted from the cell as CO, (the major product of energy-yielding respiratory metabolism or as a mixture of C02 and organic compounds, the typical end-products of fermentation metabolism). Many microorganisms can use a single organic compound to