Abstract

The study included collecting (20) soil samples from different Gypsiferious soil from Salah al-Din Governorate, Tikrit University, where it was possible to obtain (12) isolates belonging to the genus Bacillus. All bacterial isolates were subjected to microscopic, cultural and biochemical tests, which included catalase test, oxidase test, movement test, growth in anaerobic conditions, growth in (5% 70% 10%) of table salt, indole test, sterile consumption test as a sole carbon source, Fox-Proscor test, ability to decompose starch, production of gas from glucose sugar, as well as their ability to ferment (7) carbohydrate sources. The ability of the isolates to produce inhibitory substances when grown on the Nutrient broth culture medium at a temperature of (37) C for (4) days was also tested, then the filtrates of the isolates growing in the liquid medium were taken once Bs.1 and twice Bs.2 to increase their inhibitory effectiveness A filtrate without Bs.0 bacteria was used for comparison and the best isolates in all tests were identified and belonged to the species Bacillus subtilis. Also, Azospirillum sp. and Bradyrhizubium sp. were isolated from Gypsiferious soil and the three bacterial isolates were planted on Nutrient agar medium using the drilling diffusion method. The results showed that B. subtilis bacteria have inhibitory activity against Azospirillum sp. bacteria isolates (Azo1, Azo2, Azo3, Azo4, Azo5) respectively. The filtrate of the B. subtilis isolate did not give any significant inhibitory activity against Bradyrhizubium sp. bacteria isolates. Br1, Br2, Br3 Br4, Br5 respectively, The highest number of colonies was in the isolate Br4 24,17,14 CFU.10-4 respectively, at the concentration of Bs0, Bs1, Bs2 respectively, while the lowest number of colonies was in the isolate Azo5 16,1,0 respectively, at the same levels. The highest number of colonies was 24, 14 and 17 in the isolate Br4 at the concentration of Bs0, Bs1, Bs2 respectively, while it was 16,1,0 in the isolate Azo5 at the same concentration, because the highest production of inhibitory substances was 71 mg. g-1 at the concentration twice Bs2, while no secretion of inhibitory substances was recorded in all isolates in the absence of B.subtilis bacterial filtrate.

Keywords: Bacillus subtilis, Azospirillum, Bradyrhizubium, Gypsiferious, Inhibition