Identification of a new class of biopolymer: bacterial synthesis of a sulfur-containing polymer with thioester linkages

This is the first report on the biosynthesis of a hitherto unknown, sulfur- containing polyester and also the first report on a bacterial polymer conta ining containing polyester ana also the first report on a bacterial polymer con sulfur in the backbone. The Gram-negative polyhydroxyalkanoate (PHA)-a ccumulating bacterium Ralstonia eutropha synthesized a copolymer of 3-hydro xybutyrate and 3-mercaptopropionate, poly(3HB-co-3MP), when 3-mercaptopropi onic acid or 3,3'-thiodipropionic acid was provided as carbon source in add ition to fructose or gluconic acid under nitrogen-limited growth conditions . The peculiarity of this polymer was the occurrence of thioester linkages derived from the thiol groups of 3MP and the carboxyl groups of 3MP or 3HB, respectively, which occurred in addition to the common oxoester bonds of P HAs. Depending on the cultivation conditions and the feeding regime, poly(3 HB-co-3MP) contributed up to 19% of the cellular dry weight, with a molar f raction of 3MP of up to 43%. The chemical structure of poly(3HB-co3MP) was confirmed by GUMS, IR spectroscopy, H-1- and C-13-NMR spectroscopy, and ele mental sulfur analysis. The identification of this novel biopolymer reveals a new quality regarding the substrate range of PHA synthases and their cap ability for the synthesis of technically interesting polymers.