Mechanisms Of FabR Controlling Seawater Adaptation,fatty Acids Metabolisms And Virulence Gene Expression In Edwardsilla Piscicida

Edwardsiella piscicida causes severe edwardsiellosis and serious damages to the world aquaculture industries.Here,transposon insertion sequencing(TIS)was performed to explore the genetic determinants of E.piscicida survival in seawater at 16? and 28?.Disruption in 71 genes related to metabolism,transportation,and T3SS results in markedly reduced adaptaion in 16? seawater;63 genes associated with transcription,translation and energy metabolism are essential in 28? seawater.In particular,the insertions in fabR related to fatty acids metabolism increased the fitness in both temperatures while fadR mutant showed significant impaired adaptation in these temperatures,indicting that fatty acid metabolism was essential for the survival of E.piscicida in seawater.Based on the TIS results,we thus further explored the molecular mechanism of FabR regulating fatty acid metabolism,i.e.composition and ratios,and the virullence gene expression in E.piscicida by using ChIP-seq,RNA-seq and mass spectrometry.FabR directly binds to the promoter of fabA,fabB,and cfa,and regulates their expression to modulate fatty acid composition and membrane property.In addition,FabR activates the expression of oxidative phosphorylation and type III and VI secretion systems(T3/T6SS)in E.piscicida.In conclusion,FabR regulates fatty acid metabolism and composition,and controls T3/T6SS expression,demonstrating essential roles in the survival in seawater as well as the pathogenesis in vivo in fish.