Decoding and engineering tetracycline biosynthesis

Tetracyclines have been important agents in combating infectious disease since their discovery in the mid-20th century. Following widespread use, tetracycline resistance mechanisms emerged and continue to create a need for new derivatives that are active against resistant bacterial strains. Semisynthesis has led to second and third generation tetracycline derivatives with enhanced antibiotic activity and pharmacological properties. Recent advancement in understanding of the tetracycline biosynthetic pathway may open the door to broaden the range of tetracycline derivatives and afford analogs that are difficult to access by synthetic chemistry.     

Approaches to intensification and prolongation of antibiotic biosynthesis

World Journal of Microbiology and Biotechnology -     

The effect of aeration and agitation on tetracycline biosynthesis

The results of the study on relation between tetracycline biosynthesis and the specific power input for agitation in pilot plant apparatus was studied. No correlation was observed between the levels of tetracycline biosynthesis and changes in the specific power input within a range of 0.6 to 2.3 kW/m3 at the expense of changes in the mixer diameter and the agitation rate, when the aeration rate was constant. It was shown that the aeration conditions were most significant for tetracycline biosynthesis. The study provided determination of the optimal aeration conditions for biosynthesis of tetracycline.     

Interaction of actinomycetes in relation to an intensification of protease biosynthesis

This work was aimed at studying the interactions during the growth of Actinomyces rimosus producing proteases and Actinomyces violocinereus which did not synthesize secreted proteolytic enzymes. The production of proteases in the association of the actinomycetes was shown to be stimulated by metabolic products released by A. violocinereus into the surrounding medium. The stimulating agent from the cultural broth of this culture accelerated differentiation of the mycelium of the first hyphal generation in A. rimosus, decelerated spore formation of the second hyphal generation, inhibited the growth rate, and increased the rate of protease accumulation as well as the productivity of the synthesis.     

Regulation of tetracycline biosynthesis by controlling the growth of the producer]

Regulation of the rate growth of Act. aureofaciens in batch fermentation by maintaining the concentrations of phosphorus, ammonium nitrogen, glucose and pH values at the levels favourable for intensive growth at the beginning of the process and after accumulation of the biomass at the levels optimal for retarded growth of the organism resulted in significant prolongation of the period of intensive antibiotic production, i.e. intensification of the fermentation process. Microscopic investigation of the organism development under conditions of regulated fermentation revealed the presence of significant amounts of free peripheral highly basophilic hyphae for a prolonged period of time. The hyphae possessed a capacity for growth and intensive metabolism unlike the control culture which was liable to early autolysis.     

Inhibition of beta-galactosidase biosynthesis in Escherichia coli by tetracycline residues in milk.

Low levels of tetracyclines found as residues in milk inhibited the biosynthesis of beta-galactosidase in Escherichia coli. To produce the same effect, other antibacterials had to occur in concentrations that were more than 10-fold higher. This relative selectivity was exploited for the development of a screening test for tetracyclines in milk based on a chemiluminometric assay of beta-galactosidase. The method was validated with spiked samples of raw milk and applied to field samples contaminated with tetracyclines.     

Effect of dissolved carbon dioxide on the tetracycline biosynthesis process in an industrial fermenter

The data on changes in the partial pressure of carbon dioxide (pCO2) dissolved in the fermentation broth in the course of biosynthesis of tetracycline made in a 63 m3 fermenter are presented. It is shown that pCO2 equal approximately to 2 cPa was optimal for tetracycline biosynthesis. The total carbonate concentration and pCO2 were estimated simultaneously in the process of tetracycline fermentation.     

Effect of the aeration and agitation states on tetracycline biosynthesis in semiproduction-capacity apparatus]

The results of the experiments on determination of the effect of aeration and agitation conditions on biosynthesis of tetracycline in the apparatus of semi-production capacity are discussed. It was shown that the antibiotic production level was not connected with the rate of oxygen solution expressed in the sulphite numbers, i.e. this parameter cannot be used as a scaling-up criterion. Accumulation of the antibiotic in the fermentation broth depended on the volume of the air supplied for aeration. It was determined that the level of CO2 dissolved in the fermentation broth did not reach the values having an inhibitory effect on the biosynthetic process.     

Aeration conditions in the process of tetracycline biosynthesis. The role of organic acids]

The effect of the aeration conditions on the content of volatile acids in the fermentation broth was studied. It was shown that deterioration of the aeration conditions during the process of biosynthesis in both flasks and 750 1 fermentors resulted in decreased levels of the antibiotic accumulation and was accompanied by a simultaneous increase in the concentration of the volatile acids in the culture fluid. Under unfavourable aeration conditions the volatile acids present in the fermentation broth in higher concentrations than under the optimal conditions had no effect. It was shown that the volatile acid concentration may be used as a parameter for the control of the aeration conditions and as an index of normal biosynthetic process.     

Macrokinetic equations of pH effect on the growth of Actinomyces aureofaciens and biosynthesis of tetracycline]

The effect of pH on the culture respiration rate at different concentrations of glucose in the medium was studied. It was found that the hydrogen ions showed their effect irrespective of the subsrate concentration in the medium. In this connection a type of macrokinetic equations of the effect of pH on the growth and antibiotic biosynthesis was chosen. The constants of the model were determined.