Theα-glucosidase inhibitor acarbose is commercially produced by Actinoplanes sp.and used as a potent drug in the treatment of type-2 diabetes.In order to improve the yield of acarbose,an efficient genetic manipulation system for Actinoplanes sp.was established.The conjugation system between E.coli carryingØC31-derived integrative plasmids and the mycelia of Actinoplanes sp.SE50/110 was optimized by adjusting the parameters of incubation time of mixed culture(mycelia and E.coli),quantity of recipient cells,donor-to-recipient ratio and the concentration of MgCl2,which resulted in a high conjugation efficiency of 29.4%.Using this integrative system,a cloned acarbose biosynthetic gene cluster was introduced into SE50/110,resulting in a 35%increase of acarbose titer from 2.35 to 3.18 g/L.Alternatively,a pIJ101-derived replicating plasmid combined with the counter-selection system CodA(sm)was constructed for gene inactivation,which has a conjugation frequency as high as 0.52%.Meanwhile,almost all 5-flucytosine-resistant colonies were sensitive to apramycin,among which 75%harbored the successful deletion of targeted genes.Using this replicating vector,the maltooligosyltrehalose synthase gene treY responsible for the accumulation of component C was inactivated,and component C was eliminated as detected by LC-MS.Based on an efficient genetic manipulation system,improved acarbose production and the elimination of component C in our work paved a way for future rational engineering of the acarbose-producing strains.
Qinqin ZhaoHuixin XieYao PengXinran WangLinquan Bai
The highly potent antitumor agent ansamitocin P3 is a macrolactam isolated from Actinosynnema pretiosum ATCC 31565. A 120-kb DNA fragment was previously identified as the ansamitocin biosynthetic gene cluster, and contains genes for polyketide assembly, precursor synthesis, post-polyketide synthesis modification, and regulation. Within the biosynthetic gene cluster, asm8 encodes an 1117-amino-acid protein with a high degree of similarity to the large ATP-binding LuxR family-type regulators. In the current study, we determined that inactivation of asm8 by gene replacement in ATCC 31565 resulted in the complete loss of ansamitocin production, and that complementation with a cloned asm8 gene restored ansamitocin biosynthesis. Interestingly, the disruption of asm8 decreased the transcription of genes responsible for 3-amino-5-hydroxybenzoate (AHBA) formation, the starter unit required for ansamitocin biosynthesis. Subsequently, feeding of exogenous AHBA to the asm8 mutant restored ansamitocin biosynthesis, which showed that Asm8 is a specific positive regulator in AHBA biosynthesis. In addition, investigation of asm8 homologs identified two new ansamitocin producers, and inactivation of the asm8 homolog in A. pretiosum ATCC 31280 abolished ansamitocin production in this strain. Characterization of the positive regulator Asm8 and discovery of the two new ansamitocin producers paves the way for further improving production of this important antitumor agent.
PAN WenQinKANG QianJinWANG LeiBAI LinQuanDENG ZiXin
