Abstract

Intertidal red algae Hypnea valentiae associated Bacillus amyloliquefaciens MTCC 12716 revealed potential inhibitory effects on the growth of drug-resistant pathogens. In the genome of B. amyloliquefaciens MTCC 12716, biosynthetic gene clusters encoding antibacterial metabolites were predicted, which might be expressed and contributed to the broad-spectrum anti-infective activity. Three homologue members of the 24-membered macrocyclic lactone family, named as bacvalactones 1–3 bearing 13-O-ethyl (1); 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate (2); and 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate-7,24-dimethyl (3) functionalities, were acquired through bioactivity-guided purification. The macrocyclic lactones displayed bactericidal activity against opportunistic pathogens causing nosocomial infections, for instance, methicillin–resistant Staphylococcus aureus (MRSA), vancomycin–resistant Enterococcus faecalis (VREfs), and multidrug-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumonia with MIC ≤ 3.0 μg/mL, whereas standard antibiotics ampicillin and chloramphenicol were active only at concentrations of ≥ 6.25 mg/mL. The biosynthetic pathway of macrocyclic lactones that are generated by trans-AT polyketide synthases through stepwise extension of an acetyl starter unit by eleven sequential Claisen condensations with malonyl-CoA was established, and the structures were correlated with the gene organization of the mln operon, which encompasses nine genes mln A-I (approximately 47 kb in size). The best binding poses for each compounds (1–3) with Staphylococcus aureus peptide deformylase (SaPDF) unveiled docking scores (≥ 9.70 kcal/mol) greater than that of natural peptide deformylase inhibitors, macrolactin N and actinonin (9.14 and 6.96 kcal/mol, respectively), which supported their potential in vitro bioactivities. Thus, the present work demonstrated the potential of macrocyclic lactone for biotechnological and pharmaceutical applications against emerging multidrug-resistant pathogens.

Key Points

•Three antibacterial bacvalactones were identified from the symbiotic bacterium.

•The symbiotic bacterial genome was explored to identify the biosynthetic gene clusters.

•Trans-AT pks-assisted mln biosynthetic pathway of the macrocyclic lactone was proposed.

•In silicomolecular interactions of the bacvalactones with S. aureus PDF were analyzed.

中文翻译：

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摆脱传统的抗生素治疗方法：海洋巨藻相关异养体的大环内酯可以替代吗？

摘要

潮间带红藻呼吸暂停相关的解淀粉芽孢杆菌MTCC 12716显示出对耐药病原体生长的潜在抑制作用。在解淀粉芽孢杆菌MTCC 12716的基因组中，预测了编码抗菌代谢物的生物合成基因簇，其可能被表达并有助于广谱抗感染活性。24元大环内酯系列的三个同系物成员，命名为bacvalactones 1 - 3轴承13- ø -乙基（1）; 15- ø -呋喃-13- ø -异丁基-7- ø -丙基-丙酸甲酯（2）; 和15- ø -呋喃-13- ø -异丁基-7- ø -丙基-丙酸甲酯- 7,24 -二甲基（3）的功能，是通过生物活性引导纯化获得的。大环内酯对引起医院感染的机会性病原体具有杀菌活性，例如耐甲氧西林的金黄色葡萄球菌（MRSA），耐万古霉素的粪肠球菌（VREfs）以及铜绿假单胞菌和肺炎克雷伯菌的多药耐药菌株MIC≤3.0μg/ mL，而标准抗生素氨苄青霉素和氯霉素仅在≥6.25 mg / mL时才有活性。建立了反式-AT聚酮化合物合酶通过与丙二酰辅酶A进行11次连续Claisen缩合逐步逐步扩展乙酰基起始单元而生成的大环内酯的生物合成途径，并将其结构与mln操纵子的基因组织相关。涵盖了9个基因，分别为mln AI（大小约为47 kb）。对于每个化合物（最好结合姿势1 - 3与）金黄色葡萄球菌肽去甲酰基化酶（SaPDF）的对接分数（≥9.70 kcal / mol）高于天然肽去甲酰基化酶抑制剂Macrolactin N和肌动蛋白（分别为9.14和6.96 kcal / mol），这证明了其潜在的体外生物活性。因此，本工作证明了大环内酯在生物技术和药物应用中对抗新兴的多药耐药病原体的潜力。

关键点

•从共生细菌中鉴定出三种抗菌bacvalactone。

•探索了共生细菌基因组，以鉴定生物合成基因簇。

•提出了大环内酯的Trans-AT pks辅助的mln生物合成途径。

•分析了bacvalactones与金黄色葡萄球菌PDF的计算机分子相互作用。