Serrawettin W1 produced by Serratia marcescens is a surface active exolipid having various functions supporting behaviors of bacteria on surface environments. Through the genetic analyses of serrawettin-less mutants of S. marcescens 274, the swrW gene encoding putative serrawettin W1 synthetase was identified. Homology analysis of the putative SwrW demonstrated the presence of condensation, adenylation, thiolation, and thioesterase domains which are characteristic for nonribosomal peptide synthetase (NRPS). NRPSs have been known as multi-modular enzymes. Linear alignment of these modules specifying respective amino acids will enable peptide bond formation resulting in a specific amino acid sequence. Putative SwrW was uni-modular NRPS specifying only L-serine. Possible steps in this simple unimodular NRPS for biosynthesis of serrawettin W1 [ cyclo-(D-3-hydroxydecanoyl-L-seryl) (2) ] were predicted by referring to the ingenious enzymatic activity of gramicidin S synthetase (multi-modular NRPS) of Brevibacillus brevis.