The objectives of the present investigation were to characterize ammonia-producing bacteria (Bacillus sp.) and study its impact on biodeterioration of cupronickel alloy 90:10. in a nitrogen free environment. It is well known that iron sulphate and molybdenum are good inhibitors when used in a cooling water system. The interactions between inhibitor and ammonia producing bacteria on the corrosion of cupronickel 90:10 were studied. The predominated ammonia producing bacteria Bacillus sp. (AG1-EU202683; AG2-EU202684; AG3-EU202685 and AG4-EU202686) were identified by 16S rRNA gene sequencing from the biofilm. These bacteria fixed with atmospheric nitrogen for their cell protein synthesis and converted into ammonia. Ammonia enhanced pH and ammonical solution were formed in the presence of Bacillus spp. which acted as an etchant. The presence of some anodic spots in the presence of bacteria was affected by ammonia and then underwent pitting corrosion. The present study reveals that Bacillus spp. encourage intergranular attack without any stress in the cooling water system.