The genome sequence of Streptomyces rochei 7434AN4, which carries a linear chromosome and three characteristic linear plasmids

Streptomyces rochei 7434AN4 produces two structurally unrelated polyketide antibiotics, lankacidin and lankamycin, and carries three linear plasmids, pSLA2-L (211 kb), -M (113 kb), and -S (18 kb), whose nucleotide sequences were previously reported. The complete nucleotide sequence of the S. rochei chromosome has now been determined using the long-read PacBio RS-II sequencing together with short-read Illumina Genome Analyzer IIx sequencing and Roche 454 pyrosequencing techniques. The assembled sequence revealed an 8,364,802-bp linear chromosome with a high G + C content of 71.7% and 7,568 protein-coding ORFs. Thus, the gross genome size of S. rochei 7434AN4 was confirmed to be 8,706,406 bp including the three linear plasmids. Consistent with our previous study, a tap-tpg gene pair, which is essential for the maintenance of a linear topology of Streptomyces genomes, was not found on the chromosome. Remarkably, the S. rochei chromosome contains seven ribosomal RNA (rrn) operons (16S-23S-5S), although Streptomyces species generally contain six rrn operons. Based on 2ndFind and antiSMASH platforms, the S. rochei chromosome harbors at least 35 secondary metabolite biosynthetic gene clusters, including those for the 28-membered polyene macrolide pentamycin and the azoxyalkene compound KA57-A.