The use of gamma radiation in creating a mutant sub strain of Bacillus subtilis with the ability to remove ammonium in cold conditions

Abstract

Introduction: The purpose of this research was gamma ray irradiation and identification of mutant sub strains of Bacillus subtilis with high ability to remove ammonium and their adaptability to cold and use in the cold-water fishes farming biofilter water for in laboratory conditions.

Material & methods: After obtaining the effective dose of 5.8 kGy of Bacillus subtilis strain, they were irradiated with gamma rays. After that, 200 colonies were randomly selected and numbered. Each of the colonies was incubated for 1 night in a liquid culture medium suitable for ammonia oxidizing bacteria at 30°C. Potential ammonium removal colonies were isolated and cultured separately. After the screening process, the selected strains were adapted to 15 and 9 degrees Celsius. The biofilter water of a RAS trout system was prepared and the ammonium concentration increased up to 35 mg/L. Bacillus sub-strain number 180 adapted to -9◦C and 15◦C with a dilution of 108 CFU/ml was added to the enriched biofilter water and ammonium concentration was evaluated over time.

Results: The growth chart showed that among the selected strains, sub-strains 180, 62, 45 and 31 had the highest growth. The results showed that strains 62 and 180 have the highest amount of ammonium removal compared to the control group and other sub strains. Also, the results show that the removal efficiency of ammonium in biofilter water containing biofilter microbiome for fish breeding using Bacillus subtilis sub strain 180 has increased both at 15 and 9 degrees.

Conclusion: Therefore, considering the increase in the biological capacity of sub-strain number 180 to remove ammonium at low temperatures, it is suggested to use it as an effective ammonium decreasing improver in RAS systems for cold water fish farming.