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Bioremediation
Published in Domenic Grasso, Hazardous Waste Site Remediation, 2017
Catabolite repression, or substrate inhibition, occurs when a cell is faced with more than one utilizable substrate. Enzymes could be formed to catabolize all substrates, but this would be uneconomical for bacteria. Instead, enzymes are made to utilize the best substrate and only after exhaustion of the primary substrate other enzymes are formed which catabolize the “poorer” carbon sources. The most common type of catabolite repression involves the inhibition of formation of certain enzymes (i.e., repression) by the catabolite products of a readily utilizable carbon source. Catabolite repression has been historically known as the “glucose effect”, because glucose is an easily assimilable substrate, and catabolite repression of other substrates was found to occur in the presence of glucose. However, other easily utilizable substrates, such as acetate and citrate can also repress the utilization of other substrates.
Catabolite Regulation of the Main Metabolism
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
There might be a specific hierarchy for the utilization of carbon sources with glucose being on top of it, although it depends on the organisms due to their habitat and evolution. The phenomenon that the preferred carbon sources repress the synthesis of the enzymes of transport and metabolism of less favorable carbon sources is known as carbon catabolite repression (CCR) (Gorke and Stulke 2008), being more general as compared to glucose repression. Central to CCR is PTS, where it is widespread in bacteria and absent in Archeae, and eukaryotic and higher organisms (Techieu et al. 2001). The cAMP is known to mediate CCR (Magasanik 1961), where this is rather ubiquitous phenomenon observed in many organisms. The inhibitory effect of glucose uptake on cAMP synthesis is not restricted to PTS sugars, but also non-PTS sugars (Hogema et al. 1997, Bettenbrock et al. 2007).
Processes for Overproduction of Microbial Metabolites for Industrial Applications
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Carrier-mediated transportation is important because it is selective, and also because it is the rate-limiting step in the metabolism of available carbon and energy sources. As an increased rate of accumulation of metabolizable carbon source can increase the extent of catabolite repression of enzyme synthesis, the rate of metabolizable carbon transport may have widespread effects on the metabolism of the entire organism.
Mutagenesis of echinocandin B overproducing Aspergillus nidulans capable of using starch as main carbon source
Published in Preparative Biochemistry & Biotechnology, 2020
Zhong-Ce Hu, Wen-Jun Li, Shu-Ping Zou, Kun Niu, Yu-Guo Zheng
Starch is a kind of widespread carbohydrate and has been used as a cheap carbon source in fermentation, such as organic acids and antibiotics fermentation.[26] In our preliminary work, very low production was obtained when starch was used as main carbon source in echinocandin B fermentation by parent strain, A. nidulans ZJB12073. As we know, starch cannot be directly used by microorganisms, it should be enzymatic hydrolyzed to glucose by amylase. If the enzyme activity is high enough, the residual glucose in the fermentation medium will be accumulated to a high level. Too much glucose would give rise to carbon catabolite repression (CCR), resulting in much lower production of secondary metabolites.[27,28] Antibiotics are low-molecular-mass products of secondary metabolism, and one distinctive characteristic of secondary metabolism is its association with low growth rate. Non-repressing carbon sources in the medium yield low growth rate and eliminate the interference of antibiotic formation.[29] For example, biomass-specified sterigmatocystin (one of secondary metabolites in A. nidulans) production on lactose was significantly higher than on D-glucose when the low specific growth rate was attainable.[30] In this work, a mutant A. nidulans ZJB19033 capable of using starch as main carbon source instead of fructose was obtained by ARTP mutagenesis. High echinocandin B production accompanied with low specific growth rate was achieved, CCR was not observed in echinocandin B fermentation by A. nidulans ZJB19033 using starch as main carbon source.