ss00475 NtdA NTD biosynthesis operon protein NtdA ss00475 NtdB NTD biosynthesis operon putative hydrolase NtdB (EC 3.-.-.-) ss00475 NtdC NTD biosynthesis operon putative oxidoreductase NtdC (EC 1.-.-.-) ss00475 NtdR NTD biosynthesis operon regulator NtdR