Metabolic regulation of fermentation processes

A cybernetic model to predict the effect of freely available nitrogen substrate on rifamycin B production in complex media

It is well-known that secondary metabolite production is repressed by excess nitrogen substrate available in the fermentation media. Although the nitrogen catabolite repression has been known, quantitative process models have not been reported to represent this phenomenon in complex medium. In this paper, we present a cybernetic model for rifamycin B production via Amycolatopsis mediterranei S699 in complex medium, which is typically used in industry. Nitrogen substrate is assumed to be present in two forms in the medium; available nitrogen (S(ANS)) such as free amino acids and unavailable nitrogen (S(UNS)) such as peptides and proteins. The model assumes that an inducible enzyme catalyzes the conversion of S(UNS) to S(ANS). Although S(ANS) is required for growth and product formation, high concentrations were found to inhibit rifamycin production. To experimentally validate the model, five different organic nitrogen sources were used that differ in the ratio of S(ANS)/S (UNS). The model successfully predicts higher rifamycin B productivity for nitrogen sources that contain lower initial S(ANS). The higher productivity is attributed to the sustained availability of S(ANS) at low concentration via conversion of S(UNS) to S(ANS), thereby minimizing the effects of nitrogen catabolite repression on rifamycin production. The model can have applications in model-based optimization of substrate feeding recipe and in monitoring and control of fed batch processes.

Biotechnology-a sustainable alternative for chemical industry

This review outlines the current and emerging applications of biotechnology, particularly in the production and processing of chemicals, for sustainable development. Biotechnology is "the application of scientific and engineering principles to the processing of materials by biological agents". Some of the defining technologies of modern biotechnology include genetic engineering; culture of recombinant microorganisms, cells of animals and plants; metabolic engineering; hybridoma technology; bioelectronics; nanobiotechnology; protein engineering; transgenic animals and plants; tissue and organ engineering; immunological assays; genomics and proteomics; bioseparations and bioreactor technologies. Environmental and economic benefits that biotechnology can offer in manufacturing, monitoring and waste management are highlighted. These benefits include the following: greatly reduced dependence on nonrenewable fuels and other resources; reduced potential for pollution of industrial processes and products; ability to safely destroy accumulated pollutants for remediation of the environment; improved economics of production; and sustainable production of existing and novel products.

From natural products discovery to commercialization: a success story

In order for a natural product to become a commercial reality, laboratory improvement of its production process is a necessity since titers produced by wild strains could never compete with the power of synthetic chemistry. Strain improvement by mutagenesis has been a major success. It has mainly been carried out by "brute force" screening or selection, but modern genetic technologies have entered the scene in recent years. For every new strain developed genetically, there is further opportunity to raise titers by medium modifications. Of major interest has been the nutritional control by induction, as well as inhibition and repression by sources of carbon, nitrogen, phosphate and end products. Both strain improvement and nutritional modification contribute to the new process, which is then scaled up by biochemical engineers into pilot scale and later into factory size fermentors.

Effects of nutrients on the production of AK-111-81 macrolide antibiotic by Streptomyces hygroscopicus

The influence of different carbon and nitrogen sources on the production of AK-111-81 nonpolyenic macrolide antibiotic by Streptomyces hygroscopicus 111-81 was studied. Substitution of glucose with lactose or glycerol significantly affected maximal antibiotic AK-111-81 productivity as the growth rate was close to that of the basal fermentation medium. Addition of ammonium succinate to the fermentation medium markedly increased the antibiotic productivity as the growth rate was low. Divalent ions as Mn2+, Cu2+, Fe2+ stimulated AK-111-81 antibiotic biosynthesis. These results allow us to develop a new fermentation medium showing 6-fold increase of AK-111-81 antibiotic formation compared with the basal fermentation medium.

Biochemical characterization of the glucose kinase from Streptomyces coelicolor compared to Streptomyces peucetius var. caesius

Glucose kinase (Glk) from Streptomyces coelicolor was purified, characterized biochemically and kinetically, and compared to Glk from Streptomyces peucetius var. caesius. In both Streptomyces, 96% of the enzyme activity was detected in the cytosolic fraction. The use of a Glk activity gel showed no isoforms of the enzyme in extracts from these microorganisms. The purified S. coelicolor Glk was stable in its tetrameric form, unlike the purified enzyme from S. peucetius var. caesius which easily dissociated into dimers. Tetramer dissociation was prevented by 100 mM d-glucose; however, this effect was not observed with other sugars. The optimum pH and the pI are practically identical for both enzymes. Maximum activity was found at a lower temperature for S. coelicolor Glk (33 compared to 42 degrees C) and its activity was apparently less stable at higher temperatures. Its activation energy was also 40% lower than that of S. peucetius var. caesius. The kinetic mechanism appears to follow a rapid equilibrium-ordered Bi-Bi sequential mechanism in both microbial enzymes, where Glk first binds glucose and then the MgATP(2-) complex, to form a ternary complex (enzyme d-glucose-MgATP(-2)). The Km values for D-glucose and MgATP(2-) were 1.4, 0.5 mM and 1.6, 0.8 mM for the S. coelicolor and S. peucetius var. caesius Glks, respectively. However Vmax of S. coelicolor Glk was higher. In conclusion, the S. coelicolor Glk showed a more stable tetrameric form with better affinity for its substrates and higher Vmax, suggesting greater catalytic efficiency.

Antibacterial activity from Penicillium corylophilum Dierckx

A strain of Penicillium corylophilum isolated from Brazilian soil sample was submitted to different culture conditions to investigate the production of secondary metabolites with antimicrobial activity. The largest number of conidia was obtained after 5 days of incubation in oat medium and the highest level of antimicrobial activity was produced when the fungus culture was developed in the Czapek medium. The activity against Staphylococcus aureus was found only in the chloroform extract from Czapek culture broth, which also showed activity against Micrococcus luteus. Fumiquinozoline F was isolated from the active chloroform extract by using chromatographic methods. The minimal inhibitory concentration (MIC) values for M. luteus and S. aureus were 99 microg/ mL and 137microg/mL, respectively.

Lovastatin inhibits its own synthesis in Aspergillus terreus

Lovastatin suppresses its own synthesis in the microfungus Aspergillus terreus. The inhibitory effect was documented by spiking identical batch cultures with pure lovastatin (0, 50, 100 and 250 mg/l) 24 h after initiation from spores.