Carbon dioxide heterotrophic

Carbon Dioxide, Heterotrophic Assimilation (Workman and Wood) II 136... 

Carbon dioxide is produced as a result of metabolism of all heterotrophic organisms. The concentrations of CO2 in pore water of reduced sediments are therefore high. Autotrophic microorganisms consume CO2 in the oxidized part of the sediment, which can vary in depth from a meter in deep sea sediments to a few mm... 

It is important to underscore the fact that carbon dioxide is required not only for the growth of strictly phototrophic and lithotrophic organisms. Many heterotrophic organisms that are heterotrophic have an obligate requirement for carbon dioxide for their growth. Illustrative examples include the following ... 

Concerning the reduction step of the redox reaction, the heterotrophic microorganisms may use different electron acceptors. If oxygen is available, it is the terminal electron acceptor, and the process proceeds under aerobic conditions. In the absence of oxygen, and if nitrates are available, nitrate becomes the electron acceptor. The redox process then takes place under anoxic conditions. If neither oxygen nor nitrates are available, strictly anaerobic conditions occur, and sulfates or carbon dioxide (methane formation) are potential electron acceptors. Table 1.1 gives an overview of these process conditions related to sewer systems. 

FIGURE 1 Cycling of carbon dioxide and oxygen between the autotrophic (photosynthetic) and heterotrophic domainsin the biosphere. The flow of massthrough thiscycle isenormous about 4 x 1011 metric tons of carbon are turned over in the bio ihere annually. 

Common heterotrophs depend on preformed organic compounds for all three primary needs. Although some carbon dioxide is fixed in heterotrophic metabolism, the het-erotrophic cell thrives at the expense of compounds formed by other cells, and is not capable of the net conversion (fixation) of carbon dioxide into organic compounds. Some bacteria referred to as photoheterotrophs are able to regenerate ATP photochemically but cannot use photochemical reactions to supply electrons to NADP+. Such organisms are like other heterotrophs in their dependence on preformed organic compounds. But because of their photochemical... 

Water and carbon dioxide provide the most attractive and abundant source materials for the fuel products of an artificial photosynthetic device, as seen in Fig. 11. These two compounds are the outcome of the heterotrophic cycle providing the energy sources of the living organism, and the result of consumption of fossil fuels by mankind. Not surprisingly, both of the materials exhibit high chemical... 

As nonconservative gases, carbon dioxide and oxygen are closely coupled to the organic carbon pool through autotrophic (e.g., photosynthesis) and heterotrophic (e.g., respiration) processes. The dominant primary producers in estuaries and the coastal ocean are benthic and pelagic microalgae (phytoplankton). The average atomic C-to-N-to-P ratio... 

Carbon dioxide is, of course, fundamentally important to plants because of photosynthesis. Most plant cell cultures are heterotrophic, non-photosynthetic and use a chemical energy source. It is reasonable to suspect, however, that some of the control mechanisms for the photosynthetic dark reactions would be regulated by C02 concentration. This could affect both cell growth and, indirectly, production of useful compounds. More concretely, C02 is known to promote synthesis of ethylene [38] on the other hand, C02 concentrations of 5-10% inhibit many ethylene effects [53]. 

The carbon required by living organisms is an important constituent of cellular structure and metabolic compounds. This element is present in the environment in many forms. It may appear in simple form as gaseous carbon dioxide or as more complex organic compounds. Microorganisms are remarkably diverse in their carbon requirements and they are divided into two groups autotrophs and heterotrophs, based on their carbon source. 

Table II contains representative over-all reactions for methane fermentations of acetate and hydrogen, respectively. Acetate fermentation is mediated by heterotrophic organisms which use acetate as a carbon source for synthesis as well as energy. For reaction B , Ek represents the electron equivalents of the electron donor converted for energy per electron equivalent of cells synthesized. Hydrogen fermentation, by contrast, is mediated by autotrophic organisms which use carbon dioxide, acetate, or some other carbon source for cell synthesis. In the equation shown in Table II acetate was assumed to be the carbon source used as found for this fermentation by Bryant (I). E has the same definition as for heterotrophic growth.

Carbon dioxide is also fixed in the dark by photosynthetic organisms by the so-called Wood-Werkman reaction (Wood and Stjemholm, 1962). The CO2 assimilated, however, rarely exceeds that formed by dark respiration i.e. there is no net CO2 uptake. On the other hand, the amount of organic carbon derived from CO2 may be as high as 30% in heterotrophic bacteria and 90% in mixotrophic organisms. In the natural environment, non-photo-synthetic CO2 fixation by these organisms, together with the above-mentioned dark fixation by photosynthetic organisms, may under some condi-... 

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