Why are bacteria needed in the nitrogen cycle

Because atmospheric nitrogen can't be used by plants and animals. Only by soil. nitrification it is the conversion of ammonia first into nitrites then into nitrates by nitrifying bacteria and denitrification is the conversion of nitrites and nitrates into free nitrogen. Why are bacteria important to the nitrogen cycle?

Because when bacteria convert ammonia into nitrates and nitrites, producers needthem to make proteins, and then consumers eat the producers and reuse the nitrogen to make their own proteins.