Thirty-five bacterial strains capable of converting dibenzothiophene into 2-hydroxybiphenyl were isolated. Among them Rhodococcus erythropolis KA2-5-1 was chosen for further characterization because of its ability to retain high desulfurization activity stably. PCR cloning and DNA sequencing of a KA2-5-1 genomic DNA fragment showed that it was practically identical with dszABC genes from Rhodococcus sp. IGTS8, a representative carbon-sulfur-bond-targeted dibenzothiophene-degrading bacterium. KA2-5-1 desulfurized a variety of alkyl dibenzothiophenes through the specific cleavage of their C-S bonds. In addition, unexpectedly, KA2-5-1 also attacked alkyl benzothiophenes in a C-S-bond-targeted fashion. The purified monooxygenase, encoded by dszC of KA2-5-1, converted benzothiophene and dibenzothiophene into benzothiophene sulfone and dibenzothiophene sulfone, respectively, with the aid of an NADH-dependent oxidoreductase. This result raises the possibility that the same enzymatic step may be involved in desulfurization of alkylated forms of both dibenzothiophene and benzothiophene in KA2-5-1 cells.
INTRODUCTION The prawn Penaeus japonicus Kurumaebi in Japanese is one of the largest species of prawns and one of the most economically important species of shrimp in Japan. This prawn is a highly regarded food consumed as sashimi, as broiled with salt, as tempura, etc. Cultured specimens account for more than 80 of the prawn market in Japan. They are mainly cultured in Okinawa, Kagoshima, and Kumamoto Prefecture. Not only body weight and flesh quality but also body color is an important commercial quality criterion. It is well-known that the predominant pigment of the prawn is astaxanthin along with some minor yellow colored xanthophylls 1, 2. Therefore, astaxanthin is used for the pigmentation of cultured prawn 3, 4. Paracoccus carotinifaciens 5 is an aerobic gram-negative, halophilic, astaxanthin-producing bacterium and its dry-powder form is referred to PANAFERD-AX ® , which contains 3S,3 S-astaxanthin as a major carotenoid. It is used for the pigmentation of cultured fish such as salmon and trout, and has on excellent pigmentation-promoting effect on these fish 6. Therefore, we administered PAN-AFERD-AX ® for pigmentation of the prawn P. japonicus.
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