Biochemical basis of resistance to hygromycin B in Streptomyces hygroscopicus--the producing organism

Hygromycin B, an aminocyclitol Antibiotic that strongly inhibits both 70S and 80S ribosomes, is synthesized by Streptomyces hygroscopicus. Ribosomes from this Gram-positive mycelial bacterium are inhibited in vitro by the Antibiotic. In contrast, the streptomycete is highly resistant to the drug in vivo since it possesses hygromycin B phosphotransferase activity. This Enzyme has been shown by gel filtration to have a molecular weight of 42000, and to modify its Antibiotic substrate to produce 7"-O-phosphoryl-hygromycin B which totally lacks biological activity both in vivo and in vitro.