Lee Chin M, Monson Rita E, Adams Rachel M, Salmond George P C
Department of Biochemistry, University of CambridgeCambridge, United Kingdom.
Front Microbiol. 2017 Sep 11;8:1678. doi: 10.3389/fmicb.2017.01678. eCollection 2017.
Gas vesicles (GVs) are proteinaceous, gas-filled organelles used by some bacteria to enable upward movement into favorable air/liquid interfaces in aquatic environments. sp. ATCC39006 (S39006) was the first enterobacterium discovered to produce GVs naturally. The regulation of GV assembly in this host is complex and part of a wider regulatory network affecting various phenotypes, including antibiotic biosynthesis. To identify new regulators of GVs, a comprehensive mutant library containing 71,000 insertion mutants was generated by random transposon mutagenesis and 311 putative GV-defective mutants identified. Three of these mutants were found to have a transposon inserted in a LacI family transcription regulator gene () of the putative ribose operon. Each of these mutants was GV-defective; no GVs were visible by phase contrast microscopy (PCM) or transmission electron microscopy (TEM). GV deficiency was caused by the reduction of and transcription (the first genes of the two contiguous operons in the GV gene locus). Our results also showed that a mutation in was highly pleiotropic; the production of two secondary metabolites (carbapenem and prodigiosin antibiotics) was abolished. Interestingly, the intrinsic resistance to the carbapenem antibiotic was not affected by the mutation. In addition, the production of a siderophore, cellulase and plant virulence was reduced in the mutant, whereas it exhibited increased swimming and swarming motility. The RbsR protein was predicted to bind to regions upstream of at least 18 genes in S39006 including (the first gene of the ribose operon) and . Electrophoretic mobility shift assays (EMSA) confirmed that RbsR bound to DNA sequences upstream of , but not . The results of this study indicate that RbsR is a global regulator that affects the modulation of GV biogenesis, but also with complex pleiotropic physiological impacts in S39006.
气体囊泡（GVs）是由蛋白质构成的、充满气体的细胞器，一些细菌利用它在水生环境中中中向上移动到有利的气/液界面。嗜水气单胞菌（Aeromonas hydrophila）ATCC39006（S39006）是首个被发现能天然产生气体囊泡的肠杆菌。该宿主中气体囊泡组装的调控很复杂，是影响包括抗生素生物合成在内的各种表型的更广泛调控网络的一部分。为了鉴定气体囊泡的新调控因子，通过随机转座子诱变构建了一个包含71,000个插入突变体的综合突变文库，并鉴定出311个假定的气体囊泡缺陷型突变体。发现其中三个突变体的转座子插入了假定的核糖操纵子的LacI家族转录调节基因（rbsR）中。这些突变体中的每一个都是气体囊泡缺陷型；相差显微镜（PCM）或透射电子显微镜（TEM）下均未观察到气体囊泡。气体囊泡缺陷是由于gvpA和gvpC转录减少所致（它们是气体囊泡基因座中两个相邻操纵子的首个基因）。我们的结果还表明，rbsR突变具有高度多效性；两种次级代谢产物（碳青霉烯和灵菌红素抗生素）的产生被消除。有趣的是，对碳青霉烯抗生素的固有抗性不受rbsR突变的影响。此外，突变体中铁载体、纤维素酶的产生以及植物致病性降低，而其游动和群集运动性增加。预测RbsR蛋白可结合S39006中至少18个基因上游的区域，包括rbsA（核糖操纵子的首个基因）和gvpA。电泳迁移率变动分析（EMSA）证实RbsR与gvpA上游的DNA序列结合，但不与rbsA结合。本研究结果表明，RbsR是一种全局调节因子，它不仅影响气体囊泡生物合成的调控，而且对S39006具有复杂的多效生理影响。
