Sun Junyang,Gao Hongjing,Yan Danyang,Liu Yu,Ni Xianpu,Xia Huanzhang
A structurally unique aminoglycoside produced in Streptoalloteichus tenebrarius, Apramycin is used in veterinary medicine or the treatment of Salmonella, Escherichia coli, and Pasteurella multocida infections. Although apramycin was discovered nearly 50 years ago, many biosynthetic steps of apramycin remain unknown. In this study, we identified a HemK family methyltransferase, AprI, to be the 7’-N-methyltransferase in apramycin biosynthetic pathway. Biochemical experiments showed that AprI converted demethyl-aprosamine to aprosamine. Through gene disruption of aprI, we identified a new aminoglycoside antibiotic demethyl-apramycin as the main product in aprI disruption strain. The demethyl-apramycin is an impurity in apramycin product. In addition to demethyl-apramycin, carbamyltobramycin is another major impurity. However, unlike demethyl-apramycin, tobramycin is biosynthesized by an independent biosynthetic pathway in S. tenebrarius. The titer and rate of apramycin were improved by overexpression of the aprI and disruption of the tobM2, which is a crucial gene for tobramycin biosynthesis. The titer of apramycin increased from 2227 ± 320 mg/L to 2331 ± 210 mg/L, while the titer of product impurity demethyl-apramycin decreased from 196 ± 36 mg/L to 51 ± 9 mg/L. Moreover, the carbamyltobramycin titer of the wild-type strain was 607 ± 111 mg/L and that of the engineering strain was null. The rate of apramycin increased from 68% to 87% and that of demethyl-apramycin decreased from 1.17% to 0.34%.
Ming Zhao,Mingqing Zhou,Peng Gao,Xueyun Zheng,Wen Yu,Zhenyuan Wang,Jingchao Li,Jiaheng Zhang
The misuse of antimicrobials has caused a remarkable increase of antibiotic-resistant bacteria. Developing novel antimicrobial agents with high activity and low rates of resistance development is in great demand yet challenging. In this context, we developed a novel cascaded AgNPs/nGOx/Apra nanocomposite for combinational antimicrobial therapy. Glucose oxidase nanocapsules (nGOx) in the nanocomposites can convert tissue glucose into H2O2, which in turn accelerates the erosion of AgNPs into Ag+, giving rise to a synergistic antibiotic/starving-like/metal ion therapeutic effect. An in vitro antimicrobial study of the nanocomposites demonstrated rapid bacterial killing, significant bacterial growth inhibition and broad antimicrobial spectra at a low antibiotic dose. More importantly, topical and microneedle-assisted deliveries of the nanocomposites resulted in rapid scarless skin recovery in both rabbit and mouse models. This nanocomposite platform opens up a new avenue for research and clinical applications to battle against microbial infections and reduce antibiotic-resistant rates.
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