Abstract
Continued attempt by the industry and research sectors to improve productivity of commercially viable microbial products fall into three general approaches including microbial-based (e.g. isolation, selection, and manipulation of microbes as higher producers), environmental-based (e.g. media development), and bioreactor/bioprocess- based studies.
Application of electromagnetic field to microbial cultures is a recent bioprocess-based technique. Current literature shows some effects on characteristics of microbial species (fungi and bacteria). These include enhancement of ethanol production capacity of Saccharomyces cerevisiae, citric acid and cellulase production by Aspergillus niger species and insulase production by Geotrichum candidum after the cultures were exposed to electromagnetic field.
In this paper we report the application of electromagnetic field to cultures of Bacillus licheniformis to enhance productivity of bacitracin, a water-soluble branched polypeptide used as an antimicrobial agent against gram- positive and some gram-negative bacteria. Electromagnetic field was applied on cultures of B. licheniformis in stirred tank reactors (STRs) with working volume of 1.5 litres circulating into an in-house designed and constructed magnetic field generator with low magnetic field intensity. The experiments were carried out both with and without pH control of the culture. Samples were assayed for bacitracin concentration to confirm the effects of electromagnetic field. The microbial growth and pH profiles were also monitored.
The results showed that circulation of culture at flow rate of 10 mL.min-1 into magnetic field with 10 millitesla intensity leads to an increase in bacitracin concentration. The increase was higher when the pH of the culture was controlled compared to non-controlled culture. The highest percentage increase in bacitracin concentration was 36 % after 35 hours without pH control, while the highest bacitracin percentage increase obtained from the controlled culture under pH 7 exposed to electromagnetic field, was almost 89 % after 43 hours.
