ABC转运蛋白介导抗生素溶杆菌中myxin的外排机制研究

Myxin is an antimicrobial phenazine compound from Lysobacter antibioticus OH13, a soil bacterium emerging as a potential biocontrol agent. Antibiotic-producing microorganisms have evolved several self-resistance mechanisms to prevent autotoxicity. Regulation of specific transporters to improve the efflux of toxic antibiotics has been found one of the most important and intrinsic resistance strategies used by many microorganisms. ATP binding cassette (ABC) transporters belong to a superfamily of active transporters have been identified to involve in antibiotic efflux and self-resistance in bacteria. The biosynthetic mechanism of myxin has been well elucidated in our previous work, however, the efflux and regulation mechanism of myxin remains unclear. In this work, an ABC transporter encoding gene, myxA, was discovered in the myxin biosynthetic gene cluster. The mutation of myxA resulted in decrease of myxin production, which indicated that MyxA may involve in the myxin efflux in Lysobacter. And we speculate that MyxA sense and respond to myxin in Lysobacter cells depending on some upstream regulators. Here we propose to study the function of gene myxA by gene deletion, conserved domain and active site deletion. We will conduct comparative transcriptional analysis between wild type and myxA mutant to investigate other transporters possibly involved in myxin efflux. A transposon mutagenesis will be carried out to identify regulators of MyxA. The results will reveal the myxin efflux system and regulation mechanism in L. antibioticus, which will aid to improve myxin production in the future.

Myxin是从抗生素溶杆菌OH13中分离的一种吩嗪类物质，该物质对多种植物病原细菌具有显著的拮抗活性。ABC(ATP binding cassette)转运蛋白已在多种抗生素产生菌中被证明参与抗生素的外排以实现细菌的自我保护。我们在myxin合成基因簇中发现一个假定的ABC转运蛋白编码基因myxA，该基因敲除突变体的体外myxin产量与野生型相比显著降低。因此我们推测MyxA可能参与myxin的外排，并且通过某个调控因子感知myxin在体内的积累而做出应答。本项目将通过基因敲除互补、转录组测序、转座子插入诱变、EMSA等手段，明确MyxA在myxin外排中的功能，鉴定myxin的外排系统及MyxA的上游调控因子，阐明上游调控因子调控MyxA介导myxin外排的机制。研究结果将为提高抗生素溶杆菌中myxin的产量奠定基础。

Myxin是从抗生素溶杆菌中分离的一种氮氧化吩嗪类物质，该物质对多种植物病原微生物均具有显著的拮抗活性。抗生素产生菌往往通过抗生素的外排保护自身免受毒害，本项目通过阐明myxin的外排机制从而为获得myxin高产菌株提供有利条件。通过对抗生素溶杆菌OH13的基因组进行生物信息学分析，发现myxin生物合成基因簇下游存在一个ABC（ATP binding cassette）转运蛋白编码基因myxA，以及距合成基因簇较远的RND（resistance-nodulation-division）转运系统编码基因簇lexABC。将以上基因分别敲除后，myxin产量均下降，但myxA突变体对myxin的敏感性并未改变，而lexABC突变体对myxin敏感性显著增强。结果表明LexABC转运蛋白在myxin外排中至关重要，而MyxA并不是主要负责myxin外排的转运蛋白。lexABC突变后，减少的myxin通过去氧与氧甲基化而被转化为活性较低的同系物。另外，在不产吩嗪的突变体菌株△LaPhzB中，lexABC显著下调表达，而当体外添加不同浓度的myxin则可诱导其上调表达。在lexABC上游，存在一个假定编码LysR家族转录因子的基因lexR。该基因突变后，可减弱菌株对myxin的抗性，同时减少myxin产量，并且使lexABC下调表达。EMSA试验表明LexR可结合lexABC启动子区从而直接调控其表达。本研究揭示了溶杆菌中RND外排泵LexABC介导的myxin外排机制，并且lexABC的表达是通过转录调控因子LexR正向调控的。