A microorganism which is Rhodococcus rhodochrous strain NCIMB 41164 or a mutant thereof. A method of culturing the microorganism in a culture medium comprising urea or urea derivative is claimed. A nitrite hydratase obtainable from the microorganism is claimed. Also claimed is a process of preparing an amide from the corresponding nitrite wherein the nitrite is subjected to a hydration reaction in an aqueous medium in the presence of a biocatalyst selected from the group consisting of a microorganism which is a Rhodococcus rhodochrous strain NUMB 41164, a mutant thereof and a nitrite hydratase obtainable from Rhodococcus rhodochrous strain NCIMB 41164 or a mutant thereof. Also claimed is a method of storing the Rhodococcus rhodochrous NUMB 41164.