Lankamycin, produced by Streptomyces rochei 7434AN4, is a 14-membered macrolide antibiotic attached with two deoxysugars, 4″-O-acetyl-L-arcanose and D-chalcose. To reveal the order of glycosylation steps in lankamycin biosynthesis, we carried out gene disruption of two glycosyltransferase genes, lkmI and lkmL. The lkmI mutant KA50 produced 3-O-L-arcanosyl lankanolide, while the lkmL mutant KA55 accumulated two aglycons, 8-deoxylankanolide and 8,15-dideoxy-15-oxolankanolide. These results indicated that LkmL transfers L-arcanose to the C-3 hydroxyl of 8-deoxylankanolide, while LkmI does D-chalcose to the C-5 hydroxyl of 3-O-L-arcanosyl lankanolide. Taking together with previous results of gene disruption of two P450 hydroxylases, we propose a biosynthetic pathway of lankamycin including two hydroxylation and two glycosylation steps.
Two bioassay methods were established to detect root-growth accelerator(s) among metabolites of Streptomyces sp. strain MBR52. Biological activity of the water-soluble diffusate released from the mycelial mat was tested using broccoli, cucumber, and soybean seedlings. We evaluated root-growth accelerating activity of mat diffusates on adventitious roots emerging from stems of test plants. Among the plants tested, broccoli was most sensitive to the metabolites. The mat diffusate also accelerated growth of its seminal roots. Adventitious and the seminal roots responded differently to auxins. Adventitious root growth increased in response to auxins, whereas seminal root growth did not. The dry weight of adventitious roots increased in response to treatment with an aqueous solution of 0.05 mg/ml freeze-dried metabolites, while elongation of seminal roots responded only to 0.005 mg/ml. The assay methods focusing on both roots reveal different aspects of root-growth accelerating activity of the MBR52 metabolites.