A collection of nitrile-hydrolysing rhodococci was isolated from sediments
sampled from a range of deep coastal, and abyssal and hadal trench sites in
the NW Pacific Ocean, as part of our programme on the diversity of marine
actinomycetes. Nitrile-hydrolysing strains were obtained by batch enrichmen
ts on nitrile substrates with or without dispersion and differential centri
fugation pre-treatment of sediments, and were recovered from all of the dep
ths sampled (approximately 1100-6500 m). Two isolates obtained from the Ryu
kyu (5425 m) and Japan (6475 m) Trenches, and identified as strains of Rhod
ococcus erythropolis, were chosen for detailed study. Both of the deep-sea
isolates grew at in situ temperature (4 degreesC), salinities (0-4% NaCl) a
nd pressures (40-60 MPa), results that suggest, but do not prove, that they
may be indigenous marine bacteria. However, the absence of culturable Ther
moactinomyces points to little or no run off of terrestrial microbiota into
these particular trench sediments. Nitrile-hydrolysis by these rhodococci
was catalysed by a nitrile hydratase-amidase system. The hydratase accommod
ated aliphatic, aromatic and dinitrile substrates, and enabled growth to oc
cur on a much wider range of nitriles than the only other reported marine n
itrile-hydrolysing R. erythropolis which was isolated from coastal sediment
s. Also unlike the latter strain, the nitrile hydratases of the deep-sea rh
odococci were constitutive. The possession of novel growth and enzyme activ
ities on nitriles by these deep-sea R. erythropolis strains recommends thei
r further development as industrial biocatalysts.