Search

Both kanamycin A and kanamycin B, antibiotic components produced by Streptomyces kanamyceticus, have medical value. Two different pathways for kanamycin biosynthesis have been reported by two research groups. In this study, to obtain an optimal kanamycin A-producing strain and a kanamycin B-high-yield strain, we first examined the native kanamycin biosynthetic pathway in vivo. Based on the proposed parallel biosynthetic pathway, kanN disruption should lead to kanamycin A accumulation; however, the kanN-disruption strain produced neither kanamycin A nor kanamycin B. We then tested the function of kanJ and kanK. The main metabolite of the kanJ-disruption strain was identified as kanamycin B. These results clarified that kanamycin biosynthesis does not proceed through the parallel pathway and that synthesis of kanamycin A from kanamycin B is catalyzed by KanJ and KanK in S. kanamyceticus. As expected, the kanamycin B yield of the kanJ-disruption strain was 3268±255 μg/mL, 12-fold higher than that of the original strain. To improve the purity of kanamycin A and reduce the yield of kanamycin B in the fermentation broth, four different kanJ- and kanK-overexpressing strains were constructed through either homologous recombination or site-specific integration. The overexpressing strain containing three copies of kanJ and kanK in its genome exhibited the lowest kanamycin B yield (128±20 μg/mL), which was 54% lower than that of the original strain. Our experimental results demonstrate that kanamycin A is derived from KanJ-and-KanK-catalyzed conversion of kanamycin B in S. kanamyceticus. Moreover, based on the clarified biosynthetic pathway, we obtained a kanamycin B-high-yield strain and an optimized kanamycin A-producing strain with minimal byproduct. [ABSTRACT FROM AUTHOR]

Three putative regulatory genes, namely ttmRI, ttmRII and ttmRIII, which are present in the tetramycin (ttm) biosynthetic gene cluster, were found in Streptomyces ahygroscopicus. Disruption of ttmRI, ttmRII or ttmRIII reduced tetramycin production, and their complementation restored production to varying degrees. Gene expression analysis of the wild-type (WT) and mutant strains through reverse transcriptase-polymerase chain reaction (RT-PCR) of the ttm gene cluster showed that the expression levels of most of the biosynthetic genes were reduced in ΔttmRI, ΔttmRII and ΔttmRIII. Electrophoretic mobility shift assays demonstrated that TtmRI, TtmRII and TtmRIII bound the promoters of several genes in the ttm gene cluster. This study found that these three proteins are a group of positive regulators that activate the transcription of the ttm gene cluster in S. ahygroscopicus. In addition, AttmRII had a reduced degree of grey pigmentation. Thus, TtmRII has a pleiotropic regulatory function in the tetramycin biosynthetic pathway and in development. [ABSTRACT FROM AUTHOR]

Background: Isepamicin is a weakly toxic but highly active aminoglycoside antibiotic derivative of gentamicin B. Gentamicin B is a naturally occurring minor component isolated from Micromonospora echinospora. 2'-NH2-containing gentamicin C complex is a dominant compound produced by wild-type M. echinospora; by contrast, 2'-OHcontaining gentamicin B is produced as a minor component. However, the biosynthetic pathway of gentamicin B remains unclear. Considering that gentamicin B shares a unique C2' hydroxyl group with kanamycin A, we aimed to design a new biosynthetic pathway of gentamicin B by combining twelve steps of gentamicin biosynthesis and two steps of kanamycin biosynthesis. Results: We blocked the biosynthetic pathway of byproducts and generated a strain overproducing JI-20A, which was used as a precursor of gentamicin B biosynthesis, by disrupting genK and genP. The amount of JI-20A produced in M. echinospora ΔKΔP reached 911 μg/ml, which was 14-fold higher than that of M. echinospora ΔP. The enzymes KanJ and KanK necessary to convert 2'-NH2 into 2'-OH from the kanamycin biosynthetic pathway were heterologously expressed in M. echinospora ΔKΔP to transform JI-20A into gentamicin B. The strain with kanJK under PermE* could produce 80 μg/ml of gentamicin B, which was tenfold higher than that of the wild-type strain. To enhance gentamicin B production, we employed different promoters and gene integration combinations. When a PhrdB promoter was used and kanJ and kanK were integrated in the genome through gene replacement, gentamicin B was generated as the major product with a maximum yield of 880 μg/ml. Conclusion: We constructed a new biosynthetic pathway of high-level gentamicin B production; in this pathway, most byproducts were removed. This method also provided novel insights into the biosynthesis of secondary metabolites via the combinatorial biosynthesis. [ABSTRACT FROM AUTHOR]

Genetic engineering as an important approach to strain optimization has received wide recognition. Recent advances in the studies on the biosynthetic pathways and gene clusters of Streptomyces make stain optimization by genetic alteration possible. Kanamycin B is a key intermediate in the manufacture of the important medicines dibekacin and arbekacin, which belong to a class of antibiotics known as the aminoglycosides. Kanamycin could be prepared by carbamoylkanamycin B hydrolysis. However, carbamoylkanamycin B production in Streptomyces tenebrarius H6 is very low. Therefore, we tried to obtain high kanamycin B-producing strains that produced kanamycin B as a main component. In our work, aprD3 and aprD4 were clarified to be responsible for deoxygenation in apramycin and tobramycin biosynthesis. Based on this information, genes aprD3, aprQ (deduced apramycin biosynthetic gene), and aprD4 were disrupted to optimize the production of carbamoylkanamycin B. Compared with wild-type strain, mutant strain SPU313 (Δ aprD3, Δ aprQ, and Δ aprD4) produced carbamoylkanamycin B as a single antibiotic, whose production increased approximately fivefold. To construct a strain producing kanamycin B instead of carbamoylkanamycin B, the carbamoyl-transfer gene tacA was inactivated in strain SPU313. Mutant strain SPU314 (Δ aprD3, Δ aprQ, Δ aprD4, and Δ tacA) specifically produced kanamycin B, which was proven by LC-MS. This work demonstrated careful genetic engineering could significantly improve production and eliminate undesired products. [ABSTRACT FROM AUTHOR]