Microorganisms pathways

Rhee, G. Y., R. C. Sokol, C. M. Bethoney B. Bush, 1993. A long term study of anaerobic dechlorination of PCB congeners by sediment microorganisms Pathways and mass balance. Environ. Toxicol. Chem. 12 1829 1834. 

Biochemical pathways consist of networks of individual reactions that have many feedback mechanisms. This makes their study and the elucidation of kinetics of individual reaction steps and their regulation so difficult. Nevertheless, important inroads have already been achieved. Much of this has been done by studying the metabolism of microorganisms in fermentation reactors. 

The complexity of the biochemical pathways, certainly for antibiotic synthesis, means that the careful and rigorous selection of the microorganism is the key to obtaining higher titers. However, most microorganisms only show thek tme potential when cultured under optimal fermentation conditions. Of... 

Biotin is produced by a multistep pathway in a variety of fungi, bacteria, and plants (50—56). The estabUshed pathway (50,56) in E. coli is shown in Figure 6. However, Htde is known about the initial steps that lead to pimelyl-Co A or of the mechanism of the transformation of desthiobiotin to biotin. Pimelic acid is beheved to be the natural precursor of biotin for some microorganisms (51). 

The P-lactam antibiotics ate produced by secondary metaboHc reactions that differ from those responsible for the growth and reproduction of the microorganism. In order to enhance antibiotic synthesis, nutrients must be diverted from the primary pathways to the antibiotic biosynthetic sequences. Although most media for the production of penicillins and cephalosporins are similar, they ate individually designed for the specific requkements of the high yielding strains and the fermentation equipment used. 

Microorganisms exhibit nutritional preferences. The enzymes for common substrates such as glucose are usually constitutive, as are the enzymes for common or essential metabohc pathways. Furthermore, the synthesis of enzymes for attack on less common substrates such as lactose is repressed by the presence of appreciable amounts of common substrates or metabolites. This is logical for cells to consei ve their resources for enzyme synthesis as long as their usual substrates are readily available. If presented with mixed substrates, those that are in the main metabolic pathways are consumed first, while the other substrates are consumed later after the common substrates are depleted. This results in diauxic behavior. A diauxic growth cui ve exhibits an intermediate growth plateau while the enzymes needed for the uncommon substrates are synthesized (see Fig. 24-2). There may also be preferences for the less common substrates such that a mixture shows a sequence of each being exhausted before the start of metabolism of the next. 

The underlying assumption driving marine natural products chemistry research is that secondary metabolites produced by marine plants, animals, and microorganisms will be substantially different from those found in traditional terrestrial sources simply because marine life forms are very different from terrestrial life forms and the habitats which they occupy present very different physiological and ecological challenges. The expectation is that marine organisms will utilize completely unique biosynthetic pathways or exploit unique variations on well established pathways. The marine natural products chemistry research conducted to date has provided many examples that support these expectations. 

Microorganisms under anaerobic growth conditions have the ability to utilise glucose by the Embden-Mereyhof-Parnas pathway.4 Carbohydrates are phosphorylated through the metabolic pathway the end products are two moles of ethanol and carbon dioxide.5... 

Steinbuchel, A. and Lutke-Eversloh, T. 2003. Metabolic engineering and pathway construction for biotechnological production of relevant polyhydroxyalkanoates in microorganisms. Biochemical Engineering Journal 16 81-96. 

---