Influence of nitrogen source and pH value on undesired poly(γ-glutamic acid) formation of a protease producing Bacillus licheniformis strain
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Bacillus spp. are used for the production of industrial enzymes but are also known to be capable of producing biopolymers such as poly(γ-glutamic acid). Biopolymers increase the viscosity of the fermentation broth, thereby impairing mixing, gas/liquid mass and heat transfer in any bioreactor system. Undesired biopolymer formation has a significant impact on the fermentation and downstream processing performance. This study shows how undesirable poly(γ-glutamic acid) formation of an industrial protease producing Bacillus licheniformis strain was prevented by switching the nitrogen source from ammonium to nitrate. The viscosity was reduced from 32 to 2.5 mPa s. A constant or changing pH value did not influence the poly(γ-glutamic acid) production. Protease production was not affected: protease activities of 38 and 46 U mL−1 were obtained for ammonium and nitrate, respectively. With the presented results, protease production with industrial Bacillus strains is now possible without the negative impact on fermentation and downstream processing by undesired poly(γ-glutamic acid) formation.
KeywordsProtease and amylase production Bacillus licheniformis Poly(γ-glutamic acid) Ammonium Nitrate
Dissolved oxygen tension (%)
Optical density at 600 nm (−)
Oxygen transfer rate (mmol L−1 h−1)
The Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) and Henkel AG & Co. KGaA (Düsseldorf, Germany) are kindly acknowledged for partly funding this work through the joint research project “Industrieinitiative GenoMik Design” (Support Code 0313917D). Henkel AG & Co. KGaA (Düsseldorf, Germany) is also kindly acknowledged for providing the used Bacillus licheniformis strain.
Conflict of interest
The authors declare that they have no conflict of interest.
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