The correct option is C Denitrifying bacteria
Denitrification is the biological conversion of nitrate to nitrogen gas, nitric oxide or nitrous oxide. These compounds are gaseous compounds and are not readily available for microbial growth; therefore they are typically released to the atmosphere. Denitrifiers belong to several genera including Pseudomonas,Bacillus, Spirillum, Hyphomicrobium, Propionobacterium, Cornebacterium, Thiobacillus, and Alcaligenes. Biological denitrification is an anaerobic respiration reaction in which nitrate is reduced. Denitrifying bacteria are aerobic autotrophs or heterotrophs that can switch to anaerobic growth when nitrate is used as an electron acceptor.
So, the answer is option C.