Liu Huizhong, Xiao Yujie, Nie Hailing, Huang Qiaoyun, Chen Wenli
State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China.
State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
Microbiol Res. 2017 Nov;204:1-8. doi: 10.1016/j.micres.2017.07.003. Epub 2017 Jul 8.
The global regulatory molecule (p)ppGpp is synthesized under limited nutrition conditions and involves in many cellular processes in bacteria. (p)ppGpp has been reported to affect biofilm formation in several bacterial species. Here, we found that deletion of (p)ppGpp synthase genes of Pseudomonas putida KT2440 led to enhanced biofilm formation in polystyrene microtitre plates. Besides, the pellicle of this mutant formed at the air-liquid interface lost the robust structure and became frail. The biofilm formation and its structure are mainly determined by exopolysaccharides (EPSs) and adhesins. Transcriptional analysis of four EPS operons designated as pea, peb, alg and bcs and two adhesin genes nominated as lapA and lapF showed that the deletion of (p)ppGpp synthase genes increased the expression of peb, bcs and lapA but repressed the expression of pea and lapF. Furthermore, expression of the regulation factor FleQ was significantly augmented in (p)ppGpp-synthase mutants while the expression of sigma factor RpoS was reduced. Since FleQ and RpoS play important roles in regulating expression of EPS and adhesin genes, (p)ppGpp may mediate the synthesis of biofilm matrix via influencing these regulators to control the biofilm formation and pellicle structure.
全局调控分子(p)ppGpp在营养条件有限的情况下合成，并参与细菌的许多细胞过程。据报道，(p)ppGpp会影响几种细菌物种中的生物膜形成。在此，我们发现恶臭假单胞菌KT2440的(p)ppGpp合酶基因缺失导致在聚苯乙烯微量滴定板中生物膜形成增强。此外，该突变体在气液界面形成的菌膜失去了坚固的结构，变得脆弱。生物膜的形成及其结构主要由胞外多糖(EPSs)和粘附素决定。对四个名为pea、peb、alg和bcs的EPS操纵子以及两个名为lapA和lapF的粘附素基因进行转录分析表明，(p)ppGpp合酶基因的缺失增加了peb、bcs和lapA的表达，但抑制了pea和lapF的表达。此外，调控因子FleQ的表达在(p)ppGpp合酶突变体中显著增加，而σ因子RpoS的表达降低。由于FleQ和RpoS在调节EPS和粘附素基因的表达中起重要作用，(p)ppGpp可能通过影响这些调节因子来介导生物膜基质的合成，从而控制生物膜的形成和菌膜结构。
