Several enzyme-inhibitor-producing actinomycetes were isolated from various samples collected from the
marine environment and characterized. Most of them produced novel compounds that are useful in
medicine and agriculture. Actinomycete strain no. 18, which produces antibiotics against Gram-positive
bacteria only in the presence of seawater, was isolated from sediment sampled from neritic sea water and
characterized. The production of antibiotics was observed at seawater concentrations ranging from 60 to
110% (v/v). Thus, the production was seawater-dependent. The production of tetrodotoxin (TTX), known
otherwise as puffer fish toxin, was investigated in various actinomycetes collected from the marine environment.
Of 10 isolates from various sea areas, 9 produced TTX as judged by their retention times on highperformance
liquid chromatography (HPLC). To our knowledge, this is the first report of actinomycetes
from the marine environment that produce TTX.