Investigation of the Effect of Static Magnetic Field on Production of Industrially Viable Microbial Products

Static magnetic field (MF) has a range of applications in pharmaceutical and biotechnology industries from medical devices and tissue engineering to wastewater treatment. The effect of MF on microbial cultures has been investigated by some researchers. However, the findings have been inconsistent. Extensive, systematic and comprehensive investigations are needed before potential application of MF in the industry.

The aim of this research was to investigate the effect of MF on Gram-positive and Gram-negative bacterial strains for production of industrially viable products. To this end, an MF generator (MFG) was coupled with small-scale 100 mL shaken flasks (SFs) and bench-top 2 L stirred tank bioreactors (STRs). The effect of MF on two Gram-positive (Bacillus licheniformis NCIMB 8874 and Bacillus subtilis NCTC 3610) and one Gram-negative (Pseudomonas putida KT2440) bacterial strains was investigated with focus on production of two industrially viable products (bacitracin A and polyhydroxybutyrate (P(3HB)). P(3HB) was chosen as a valuable product of recent interest, produced by both Gram-negative and Gram-positive bacteria, making it a good candidate for this research. Bacitracin A was chosen as a model antibiotic produced by B. licheniformis.

Experiments were carried out in SF cultures of B. licheniformis with circulation rate of 10 mL. min-1 through MFG producing 28 mT static MF. While there was no notable difference in the specific growth rate between the test and the control cultures, a decrease in the highest concentration of bacitracin A by 23% was observed. Subsequently, the experiment was extended to 2 L STRs with the same circulation rate (10 mL. min-1), but at two MF intensities of 28 mT and 10 mT. The former, showed no notable effect on bacitracin A production or cell growth. The latter experiment, however, resulted in 27% increase in the highest bacitracin A concentration. As bacitracin A concentration in the culture medium started to decrease due to unfavourable alkaline conditions, the next fermentation was carried out under pH control at 6-7. In this fermentation, bacitracin A concentration continued to increase in both MF exposed and control cultures without a notable difference between the two. However, substrate uptake, growth profile and total carbohydrate concentrations changed considerably. These changes suggest a shift in cellular metabolism leading possibly to biosynthesis of other products including extracellular polymeric substances.

The STR system was then coupled with MFG of 18 and 28 mT intensities at a circulation rate of 10 mL. min-1, and used for production of P(3HB) by B. subtilis and P. putida. Neither of the two MF intensities led to any considerable changes in growth profile, cell morphology or P(3HB) production in B. subtilis STR system. On the other hand, a considerable change in morphology was observed in P. putida cultures. Also, P(3HB) concentration in the culture exposed to MF increased by 15% under 18 mT and by 29% under 28 mT. These novel findings suggest a great scope for further investigations of this system for potential industrial applications.