Mayumi Shinose

Complete genome sequence and comparative analysis of the industrial microorganism Streptomyces avermitilis.

Species of the genus Streptomyces are of major pharmaceutical interest because they synthesize a variety of bioactive secondary metabolites. We have determined the complete nucleotide sequence of the linear chromosome of Streptomyces avermitilis. S. avermitilis produces avermectins, a group of antiparasitic agents used in human and veterinary medicine. The genome contains 9,025,608 bases (average GC content, 70.7%) and encodes at least 7,574 potential open reading frames (ORFs). Thirty-five percent of the ORFs (2,664) constitute 721 paralogous families. Thirty gene clusters related to secondary metabolite biosynthesis were identified, corresponding to 6.6% of the genome. Comparison with Streptomyces coelicolor A3(2) revealed that an internal 6.5-Mb region in the S. avermitilis genome was highly conserved with respect to gene order and content, and contained all known essential genes but showed perfectly asymmetric structure at the oriC center. In contrast, the terminal regions were not conserved and preferentially contained nonessential genes.

Genome sequence of an industrial microorganism Streptomyces avermitilis: Deducing the ability of producing secondary metabolites

Streptomyces avermitilis is a soil bacterium that carries out not only a complex morphological differentiation but also the production of secondary metabolites, one of which, avermectin, is commercially important in human and veterinary medicine. The major interest in this genus Streptomyces is the diversity of its production of secondary metabolites as an industrial microorganism. A major factor in its prominence as a producer of the variety of secondary metabolites is its possession of several metabolic pathways for biosynthesis. Here we report sequence analysis of S. avermitilis, covering 99% of its genome. At least 8.7 million base pairs exist in the linear chromosome; this is the largest bacterial genome sequence, and it provides insights into the intrinsic diversity of the production of the secondary metabolites of Streptomyces. Twenty-five kinds of secondary metabolite gene clusters were found in the genome of S. avermitilis. Four of them are concerned with the biosyntheses of melanin pigments, in which two clusters encode tyrosinase and its cofactor, another two encode an ochronotic pigment derived from homogentiginic acid, and another polyketide-derived melanin. The gene clusters for carotenoid and siderophore biosyntheses are composed of seven and five genes, respectively. There are eight kinds of gene clusters for type-I polyketide compound biosyntheses, and two clusters are involved in the biosyntheses of type-II polyketide-derived compounds. Furthermore, a polyketide synthase that resembles phloroglucinol synthase was detected. Eight clusters are involved in the biosyntheses of peptide compounds that are synthesized by nonribosomal peptide synthetases. These secondary metabolite clusters are widely located in the genome but half of them are near both ends of the genome. The total length of these clusters occupies about 6.4% of the genome.

Screening and fermentation of endo-α-N-acetylgalactosaminidase S, a mucin-hydrolyzing enzyme from Streptomyces acting on the GalNAc-O-Ser (Thr) linkage

Abstract Soil microorganisms were examined for their ability to grow on porcine gastric mucin as a sole source of carbon and energy. Streptomyces sp. OH-11242 thus selected was found to produce endo-α- N -acetylgalactosaminidase (endo-GalNAc-ase S), together with several mucin-degrading glycosidases. Endo-GalNAc-ase S is a new enzyme capable of hydrolyzing the innermost GalNAc- O -Ser (Thr) linkage of the mucin molecule. Studies on the fermentation conditions necessary for its production revealed that the enzyme was induced by mucin but the induction was inhibited by glucose and other easily assimilable carbon sources, as well as by complex nitrogen sources. Addition of palmitate, λ-carrageenan, or crude mucin to a mucin-based production medium enhanced enzyme production and mycelial growth. When the initial mucin concentration of the production medium was increased, the maximum titer of endo-GalNAc-ase S produced in the culture both also increased, while the cultivation time giving the peak enzyme titer was prolonged. As a result of the studies, increased and reproducible production of endo-GalNAc-ase S was achieved, reaching 42 units/ml in a 100-ml culture and 31 units/ml in an 800-ml culture with 2 and 1.5% purified mucin, respectively, as the major carbon source.