A Gram-negative,red-pigment-producing bacterial strain(designated as YD25)was isolated from plant rhizosphere soil.Cells of strain YD25 are short rods,1.2~1.4×0.6~0.7 rn and possess week flagella.The strain YD25 can utilize L-Arabinose and D-xylose which is different from Serratia marcescens.Besides,it was different from S.rarcescens that the major fatty acid components of strain YD25 shared 71.8%similarity with Cedeceadavisae in the MIDI database.The phylogenetic tree inferred from the 16S rRNA sequences showed that strain YD25 formed an out group to the clade containing S.marcescens subsp.sakuensis KRED and S.marcescens subsp.marcescens DSM 30121.While the rpoB gene tree demonstrated that strain YD25 formed a cluster with S.marcescens subsp.marcescens Db11.On the basis of the data presented,strain YD25 was confnrmed to be a new subspecies of S.marcescens.By liquid chromatography,mass spectrometry and nuclear magnetic resonance,we found that the main antibacterial compounds simultaneously produced by S.marcescens YD25 were prodigiosinand serrawettin W2.According to the antibacterial tests,serrawettin W2 showed potent antimicrobial activity against the tested Gram-positive and Gram-negative bacteria,including nine clinical isolates Staphylococcus aureus strains.Meanwhile,serrawettin W2 could inhibit the growth of Hela cells but showed less cytotoxicity to nonmalignant cell lines.So far,S.marcescens strains which could produce more than one kind of serrawettin had not been recognized.Thus,S.marcescens YD25 is the first one which could produce a mixture of serrawettin W2congeners simultaneously.Analysis of the draft genome sequence of S.marcescens YD25 resulted in the identification of aputative cyclic lipopeptide(CLP)antibiotics serrawettin W2 biosynthesis gene cluster,which is a total of 28 kb interrupted DNAsequence containing polyketide synthases(PKS)gene and non-ribosomal peptide synthetases(NRPS)gene.The PKS gene is consisted of a ketosynthase(KS),a ketoreductase(KR)andanenoyl reductase(ER)domain.In the putative NRPS gene,there areatotal of five modules and each module consists of condensation(C),adenylation(A)and thiolation(T)domains and the five modules harbors one thioesterification(TE)domain.The genome-based identification and structure prediction of serrawettin W2provides the proof of the detailed chemical analyses in the S.marcescens YD25.