THE CARBON SOURCE

The TCA-cycle functions to convert pyruvic and lactic acids, the end products of anaerobic glycolysis (EMP), to CO2 and H2O. It also is a common channel for the ultimate oxidation of fatty acids and the carbon skeletons of many amino acids. The overall reaction is  

The PPP handles pentoses and is important for nucleotide (ribose-5-phosphate) and fatty acid biosynthesis (NADPH2). The Entner-Doudoroff pathway catabolizes glucose into pyruvate and glyceraldehyde-3-phosphate. It is important primarily in Gram negative prokaryotes.  

HSCH2CH(NH2)C00H Cysteine (amino acid) C,N,H,0,S ] proteins 

CH3(CH2)i4C00H Palmitic acid (fatty acid) C,H,0 fats and oils 

T able 3. Average composition (%) of European (A) and U. S. (B) beet molasses versus Brazilian/Caribbean blackstrap molasses samplesf l 

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In operations similar to the E. ashbjii procedures, the closely related fungus Jishbjagossjpii gave similar yields. Thus, a yield of 7.3 g/L was obtained with a lyoptulked culture in a medium containing fat, leather glue, and com extracts (50), and 6.420 g/L with bone or hide fat, alone or in a mixture with other plant or animal fats as the carbon source (51). The yield from immersed cultures ofM. gossjpii was increased to 6.93—7.20 g/L by use of waste fats or technical cod-Hver oil (52). 

Riboflavin is also made by aerobic culturing of Pichiaguilliermondii on a medium containing n-Q g-Q paraffins in a yield of 280.5 mg/L (53). A process employing Pichia yeasts, such as P. miso, P. miso Mogi, or P. mogii, in a medium containing a hydrocarbon as the carbon source, has been patented... 

Further efficient fermentative methods for manufacture of riboflavin have been patented one is culturing C. famata by restricting the carbon source uptake rate, thereby restricting growth in a linear manner by restriction of a micronutrient. By this method, productivity was increased to >0.17 g riboflavin/L/h (63). The other method, using Bacillus subtilis AJ 12644 low in guanosine monophosphate hydrolase activity, yielded cmde riboflavin 0.9 g/ L/3 days, when cultured in a medium including soy protein, salts, and amino acids (64). 

Cheese whey soHds contain 70—75% lactose, which can serve as the carbon source for lactose fermenting yeasts such as Klujveromjcesfragilis. The total volume produced is considerably smaller than for the other yeasts described. 

By beginning with methane, the diamonds formed have only in them. These tiny diamonds may then be used as the carbon source to form large (5 mm) single crystals by growth from molten catalyst metal in a temperature gradient. The resulting nearly pure crystals have outstanding thermal conductivities suitable for special appHcations as windows and heat sinks (24). 

As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised and filled with fresh medium prior to inoculation. For some processes, addition of all the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the lifetime of batch cultures and thus product yields fed-batch cultures are considered further in Section 2.7.4. 

We can see that for type 1 processes, high growth rate is obligately linked to a high rate of product formation. Indeed, this is the case for all products produced by a fermentative mode of metabolism, eg ethanol, lactic add, acetone. Chemostat studies have shown that for most aerobic processes when growth is limited by some nutrient other than the carbon source, the yield of product decreases with increase in spedfic growth rate (p or D p = dilution rate (D) in chemostat culture). Conversely, both the biomass yield and the spedfic rate of substrate utilisation (qs g substrate g biomass-1 h-1) increase with spedfic growth rate. 

Trace metals have to be removed, notably manganese, ferrous ions and zinc. This is often accomplished using the compound potassium hexacyanoferrate which predpitates or complexes the metals and, in excess, acts to inhibit growth and indirectly promotes dtric add production. The amount of potassium hexacyanoferrate required is variable depending on the nature of the ion content of the carbon source. 

These limitations have been overcome by the development of strains able to grow well in a minimal salts medium in the absence of complex nutrients and vitamins. The carbon source is usually glucose and a complex nitrogen source, such as glutamate, can replace ammonia. 

Explain why it would be inadvisable to use the carbon source as growth limiting nutrient in the sucdnoglycan fermentation. 

One of the commercial methods for production of lysine consists of a two-stage process using two species of bacteria. The carbon sources for production of amino acids are corn, potato starch, molasses, and whey. If starch is used, it must be hydrolysed to glucose to achieve higher yield. Escherichia coli is grown in a medium consisting of glycerol, corn-steep liquor and di-ammonium phosphate under aerobic conditions, with temperature and pH controlled. 

The carbon source affects oxygen demand. In penicillin production, oxygen demand for glucose is 4.9 mol 1 1 h-1. The lactose concentration is 6.7 mol 1 1 h 1, sucrose is 13.4 mol l-1 h. The yield of oxygen per mole of carbon source for CH4 is YQjC = 1.34, T0j/C for Paraffins = 1, and Y(> /c for hydrocarbon (CH20)n = 0.4. The mass transfer coefficient k,a is for gas-liquid reactions, and the film thickness where the mass transfer takes place is 8... 

Table 3.1 shows the kinetic parameters for cell growth, rate models with or without inhibition and mass transfer coefficient calculation at various acetate concentrations in the culture media. The Monod constant value, KM, in the liquid phase depends on some parameters such as temperature, initial concentration of the carbon source, presence of trace metals, vitamin B solution, light intensity and agitation speeds. The initial acetate concentrations in the liquid phase reflected the value of the Monod constants, Kp and Kp. The average value for maximum specific growth rate (/xm) was 0.01 h. The value... 

Microbial over-growth was controlled with carbon dioxide passed through the bed. There was a maximum 30% increase in the beads diameter at the lower part of column, where the glucose concentration was maximum. The void volume was measured by passing sterilised water. In addition to the carbon source, the feeding media consisted of 1 g l 1 yeast extract pumped from the bottom of the reactor, while the flow rate was constant for a minimum duration of 24 hours. 

Figure 9.9 shows the flow sheet for stoichiometry and material balance in a cell. According to the problem, two thirds of the carbon source goes to biomass. 

There are various grades of activated carbon, depending on the carbon source and the ultimate application types include coconut shells,... 

Zirconium carbide has also been deposited from the tetrachloride with methane or cyclopropane as the carbon source,... 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

Previously, Yu et al (2005) studied the increase of a co-biopolymer of PHBV by Ralstonia eutropha in a continuous stirred tank reactor. It was found that the productivity rate increased when sodium propionate was used as the carbon source. Later, Yezza et al (2007) investigated the use of maple sap as a carbon for PHB production by A. latus. The productivity of PHB reached 2.6 gH h-i. 

When to stop a fermentation is a very complex decision and several factors have to be taken into account. Quite often a manufacturer will find it appropriate to harvest shortly after the first signs of a faltering in the efficiency of conversion of the most costly raw material (the carbon source, e.g. glucose) into penicillin. 

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