Simultaneous Production of Prodigiosin and Serrawettins As the Main Bioactive Compounds By Serratia surfactantfaciens Sp. Nov

A Gram-negative, red-pigmented bacterial strain YD25^T was isolated from rhizosphere soils under continuously planting burley tobacco in Fujian Province, China. The bacterium was characterized by a polyphasic approach, including 16S rRNA gene sequence analysis, multilocus sequence analysis (MLSA), ortho average nucleotide identity (OrthoANI) calculations, genome to genome distance calculator (GGDC) analysis, fatty acid methyl esters analysis, determination of DNA G+C content and an analysis of phenotypic features. On the basis of 16S rRNA gene sequence similarity, strain YD25^T was shown to be related to Serratia nematodiphila DSM 21420^T (99.53 %) and S. marcescens LMG 2792^T (99.47 %), respectively. However, the results of MLSA, OrthoANI calculations, GGDC analysis as well as physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain YD25^T from recognized Serratia species. On the basis of polyphasic characterization data obtained in the present study, the strain YD25^T as a new species for which the name Serratia surfactantensis sp. nov., is proposed, with YD25^T (=CCTCC M2013617^T) being designated as the type strain.

By liquid chromatography, mass spectrometry and nuclear magnetic resonance, the main antibacterial compounds simultaneously produced by S. surfactantensis YD25^T were identified to be prodigiosin and serrawettin W2. In addition, S. surfactantensis YD25^T produces another six homologous of serrawettin W2. So far, S. surfactantensis YD25^T is the first one which produces prodigiosin and a mixture of serrawettin W2 analogues simultaneously. According to the antibacterial tests, serrawettin W2 shows potent antimicrobial activity against the tested Gram-positive and Gram-negative bacteria, including nine clinical isolates Staphylococcus aureusstrains. Meanwhile, serrawettin W2 inhibits the growth of Hela cells and shows less cytotoxicity to nonmalignant cell lines.

Analysis of the draft genome sequence of S. surfactantensis YD25^T resulted in the identification of a putative cyclic lipopeptide (CLP) antibiotics serrawettin W2 biosynthesis gene cluster. The biosynthesis gene cluster is a total of 28 kb interrupted DNA sequence containing polyketide synthases (PKS) gene and non-ribosomal peptide synthetases (NRPS) gene. The PKS gene is consisted of a ketosynthase (KS), a keto reductase (KR) and an enoyl reductase (ER) domain. In the putative NRPS gene, there are a total 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 W2 provides the proof of the chemical analyses in the S. surfactantensis YD25^T.