Many economically valuable microbial products are secondary metabolites. Section 11.3 Large-scale industrial fermentations present several engineering problems. In aerobic processes, ensuring adequate oxygen availability in a large industrial tank is a difficult problem, requiring installations for stirring and aeration. The microbial process must be continuously monitored in order to ensure satisfactory yields of the desired product. Section 11.4 Scale-up is the process of gradually converting a useful industrial fermentation from laboratory scale to production scale.
Aeration is a particularly critical aspect to monitor during scale-up studies.
The industrial production of antibiotics begins with screening for antibiotic producers. Once new producers are identified, purification and chemical analysis of the antimicrobial agent can be made. If the new antibiotic is biologically active in vivo, the industrial microbiologist may genetically modify the producing strain to increase yields to levels acceptable for commercial development. Section 11.6 Major antibiotics of clinical significance include the -lactam antibiotics penicillin and cephalosporin, and the tetracyclines. All of these antibiotics are typical secondary metabolites, and their industrial production is well worked out despite the fact that the biochemistry and genetics of their biosynthesis are only partially understood.