Identification Of Genes Encoding Acyltransferases Of Lipid A In Cronobacter Sakazakii

Cronobacter sakazakii is a ubiquitous food-borne pathogen. C. sakazakii cancontaminate infant formula powder and infect infants, neonates, causing meningitis,septisemia, bacteremia necrotizing conjunctivitis, but its pathogenic mechanism is notvery clear. Rencent studies show that the pathogenicity of some gram-negative bateriais closely related to the structure of lipid A, which is located in the outer membrane ofbacteria. Therefore, the lipid A structure and biosynthetic pathway in C. sakazakiilipid A were need to be further studied.It was confirmed that the lipid A of C. sakazakii is different from that ofEscharicha coli, mainly in the secondary fatty acid acyl chain. Three genes encodedfor lipid A acyl chain acyltransferase have been identified. The main conclusions areas follows:（1）Three genes ESA02293, ESA02951and ESA01386of C. sakazakiiBAA894have been identified by BLAST search. These genes share79%,71%,75%identity to E. coli lpxL, lpxP and lpxM, respectively.（2）Over expression of ESA02293in E. coli lipid A mutant MKV15andMLK1067show that the ESA02293encoded enzyme can transfer C14:0acyl fattyacid to the2′position of lipid A, which was named as CslpxL.（3）Over expression of ESA02951in MKV15b and MLK1067show that theenzyme encoded by ESA02951can transfer either C16:1or C14:0acyl fatty acidchain to the2′position of lipid A. After grown at12°C, the dominant structure of lipidA in C. sakazakii BAA894is with C16:1acyl fatty acid chain at2′position. TheESA02951was named as CslpxP.（4）Over expression of ESA01386in MKV15b and MLK1067show that theenzyme encoded by ESA01386can transfer either C14:0or C12:0acyl fatty acidchain at3′position, which was named as CslpxM.（5）Over co-expression of CslpxL, CslpxM, EclpxL and EclpxM, the function ofCslpxM was further confirmed, which can transfer either C14:0or C12:0acyl fattyacid chain to the3′position of lipid A.（6）The number of fatty acid chain of lipid A can affect cell surfacehydrophobicity, cell autoaggregation and biofilm formation.In summary, this study has identified three genes (ESA02293, ESA02951, andESA01386) encoding acyltransferases of lipid A in C. sakazakii BAA894by gene expression and mass spectrometry, which can contribute to the diversity of lipid A inC. sakazakii BAA894.