The Interaction Between Two Flagellar Systems Of Shewanella Piezotolerans WP3

Flagella are extremely effective organelles used by a variety of bacteria forlocomotion, which can help bacteria moving toward favorable enviroments oravoiding harmful enviroment, thus, flagella are crucial for bacteria survival andsuccessful competition with other micro-organisms. Bacteria will coordinate theflagella number even types according to different enviroments. Bacteria expressingonly lateral flagella will enhance the flagella expression when moving in visciousenvironment or surface. Bacteria possess two types of flagella express only polarflagellum when moving in liquid, while living in the environment not favorable forpolar flagellum, lateral falgella will be induced.Shewanella piezotolerans WP3, which was isolated from deep-sea sediments of1914m depth in West Pacific, is an ideal material to study the adaptation mechanismof extremophiles to the extreme environments. WP3possesses two different types offlagellar systems, which are regulated by pressure and temperature respectively. Inthis study, We focused on the dual flagellar systems of WP3. Identified the interactionbetween these two flagellar systems.After the deletion of polar flagellar gene flgH1or flgL1, the swimming motilityof WP3significantly decreased, but didn’t lost it completely. When we deleted thepolar and lateral flagellar gene simultaneously, the swimming motility of WP3completely lost. the results indicate that these two genes flgH and flgL areindispensable for flagellar function.The Transmission electron microscopy results of two polar flagellar mutantsflgH1and flgL1show that they expressed lateral flagella when cultivated in liquidmedium under20℃. These results indicate that WP3have developed a mechnismwhich can sense the defection of polar flagellum, and therefore express lateralflagella.In order to verify whether the structural genes of two flagellar systems were ableto complement each other, we constructed a double mutant flgH1flgL2. The motility assay show that flgH1flgL2could swim but could not swarm,indicatingthat the defection of polar flagellar genes can be compensated by lateral flagellargenes.In addition, the results of motility assay of WP3mutants show that, the mutantsexpress polar flagellum could swim faster than the mutants express lateral flagellawhen cultured at20℃. while cultured at4℃, the results were reversed.After the musurement of the growth curve of mutants, we found that the OD600of those expressing polar flagellum decresed significantly when come to stationaryphase. The others didn’t show this feature. This result indicates that the polarflagellum plays an important role in the biofilm formation.