Poly(hydroxyfettsäureester), eine fünfte Klasse von physiologisch bedeutsamen organischen Biopolymeren?

Biodegradable Polyhydroxyalkanoates by Stereoselective Copolymerization of Racemic Diolides: Stereocontrol and Polyolefin-Like Properties

Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side-chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chemical synthesis of bacterial PHAs has been developed, using the metal-catalyzed stereoselective ring-opening (co)polymerization of racemic cyclic diolides (rac-8DL^R , R=alkyl group). In this combined experimental and computational study, polymerization kinetics, stereocontrol, copolymerization characteristics, and the properties of the resulting PHAs have been examined. Most notably, stereoselective copolymerizations of rac-8DL^Me with rac-8DL^R (R=Et, Bu) have yielded high-molecular-weight, crystalline isotactic PHA copolymers that are hard, ductile, and tough plastics, and exhibit polyolefin-like thermal and mechanical properties.

Homoserine Lactones, Methyl Oligohydroxybutyrates, and Other Extracellular Metabolites of Macroalgae-Associated Bacteria of the Roseobacter Clade: Identification and Functions

Twenty-four strains of marine Roseobacter clade bacteria were isolated from macroalgae and investigated for the production of quorum-sensing autoinducers, N-acylhomoserine lactones (AHLs). GC/MS analysis of the extracellular metabolites allowed us to evaluate the release of other small molecules as well. Nineteen strains produced AHLs, ranging from 3-OH-C10:0-HSL (homoserine lactone) to (2E,11Z)-C18:2-HSL, but no specific phylogenetic or ecological pattern of individual AHL occurrence was observed when cluster analysis was performed. Other identified compounds included indole, tropone, methyl esters of oligomers of 3-hydroxybutyric acid, and various amides, such as N-9-hexadecenoylalanine methyl ester (9-C16:1-NAME), a structural analogue of AHLs. Several compounds were tested for their antibacterial and antialgal activity on marine isolates likely to occur in the habitat of the macroalgae. Both AHLs and 9-C16:1-NAME showed high antialgal activity against Skeletonema costatum, whereas their antibacterial activity was low.

A multi-functional polyhydroxybutyrate nanoparticle for theranostic applications

One-step enzymatic synthesis of theranostic PHB nanoparticles using PHA synthase fused with A33scFv and GFP.

Ralstonia eutropha H16 flagellation changes according to nutrient supply and state of poly(3-hydroxybutyrate) accumulation

Two-dimensional polyacrylamide gel electrophoresis (2D PAGE), in combination with matrix-assisted laser desorption ionization-time of flight analysis, and the recently revealed genome sequence of Ralstonia eutropha H16 were employed to detect and identify proteins that are differentially expressed during different phases of poly(3-hydroxybutyric acid) (PHB) metabolism. For this, a modified protein extraction protocol applicable to PHB-harboring cells was developed to enable 2D PAGE-based proteome analysis of such cells. Subsequently, samples from (i) the exponential growth phase, (ii) the stationary growth phase permissive for PHB biosynthesis, and (iii) a phase permissive for PHB mobilization were analyzed. Among several proteins exhibiting quantitative changes during the time course of a cultivation experiment, flagellin, which is the main protein of bacterial flagella, was identified. Initial investigations that report on changes of flagellation for R. eutropha were done, but 2D PAGE and electron microscopic examinations of cells revealed clear evidence that R. eutropha exhibited further significant changes in flagellation depending on the life cycle, nutritional supply, and, in particular, PHB metabolism. The results of our study suggest that R. eutropha is strongly flagellated in the exponential growth phase and loses a certain number of flagella in transition to the stationary phase. In the stationary phase under conditions permissive for PHB biosynthesis, flagellation of cells admittedly stagnated. However, under conditions permissive for intracellular PHB mobilization after a nitrogen source was added to cells that are carbon deprived but with full PHB accumulation, flagella are lost. This might be due to a degradation of flagella; at least, the cells stopped flagellin synthesis while normal degradation continued. In contrast, under nutrient limitation or the loss of phasins, cells retained their flagella.

Graft copolymers containing poly(3-hydroxyalkanoates) — A review on their synthesis, properties, and applications

The use of the poly(3-hydroxyalkanoates) in copolymer synthesis has received much interest, as the microbial polyester segments can bring interesting properties, such as biodegradability and biocompatibility. The synthesis, properties, and applications of graft copolymers containing poly(3-hydroxyalkanoates) as main chain or branches are reviewed here, with emphasis on the different preparation methods, which fit into the three main synthesis strategies of graft copolymers: “grafting onto”, “grafting from”, and “grafting through” or macromonomer methods.Key words: poly(3-hydroxyalkanoates), graft copolymer, synthesis, properties, applications.

Aldol-type Reactions of Unmasked Iodoacetic Acid with Carbonyl Compounds Promoted by Samarium Diiodide: Efficient Synthesis of Carboxylic 3-Hydroxyacids and Their Derivatives

An easy, direct, general, and efficient samarium diiodide-mediated preparation of 3-hydroxyacids 1 in high yield by reaction of different aldehydes or ketones with commercially available iodoacetic acid is described. The application of different esterification procedures to the crude 3-hydroxyacids so obtained afforded the corresponding 3-hydroxyesters. Also, the cyclization of crude 3-hydroxycarboxylic acids allowed the preparation of beta-lactones. A mechanism is proposed to explain the synthesis of 3-hydroxyacids 1.

Biosynthesis of medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs) by Comamonas testosteroni during cultivation on vegetable oils

Comamonas testosteroni has been studied for its ability to synthesize and accumulate medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs) during cultivation on vegetable oils available in the local market. Castor seed oil, coconut oil, mustard oil, cotton seed oil, groundnut oil, olive oil and sesame oil were supplemented in the mineral medium as a sole source of carbon for growth and PHAs accumulation. The composition of PHAs was analysed by a coupled gas chromatography/mass spectroscopy (GC/MS). PHAs contained C6 to C14 3-hydroxy acids, with a strong presence of 3-hydroxyoctanoate when coconut oil, mustard oil, cotton seed oil and groundnut oil were supplied. 3-hydroxydecanoate was incorporated at higher concentrations when castor seed oil, olive oil and sesame oil were the substrates. Purified PHAs samples were characterized by Fourier Transform Infrared (FTIR) and 13C NMR analysis. During cultivation on various vegetable oils, C. testosteroni accumulated PHAs up to 78.5-87.5% of the cellular dry material (CDM). The efficiency of the culture to convert oil to PHAs ranged from 53.1% to 58.3% for different vegetable oils. Further more, the composition of the PHAs formed was not found to be substrate dependent as PHAs obtained from C. testosteroni during growth on variety of vegetable oils showed similar compositions; 3-hydroxyoctanoic acid and/or 3-hydroxydecanoic acid being always predominant. The polymerizing system of C. testosteroni showed higher preference for C8 and C10 monomers as longer and smaller monomers were incorporated less efficiently.

Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers

In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 x 10(5) to 6.65 x 10(5), were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state (1)H NMR data were used to determine polymer composition-of-matter, while solution-state (13)C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB-co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB-co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB-co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.

Regulation of phasin expression and polyhydroxyalkanoate (PHA) granule formation in Ralstonia eutropha H16

Regulation of expression of the phasin PhaP, which is the major protein at the surface of polyhydroxyalkanoate (PHA) granules in Ralstonia eutropha H16, was studied and analysed at the molecular level. The regulation of PhaP expression is achieved by an autoregulated repressor, which is encoded by phaR in R. eutropha. The occurrence of PhaR homologues and the organization of phaR genes was analysed in detail in 29 different bacteria. Three kinds of molecule to which PhaR binds were identified in cells of R. eutropha, as revealed by gel-mobility-shift assays, DNaseI footprinting, cell fractionation, immunoelectron microscopy studies employing anti-PhaR antibodies raised against purified N-terminal hexahistidine-tagged PhaR and in vitro binding studies employing artificial PHA granules. PhaR binds upstream of phaP at two sites comprising the transcriptional start site plus the -10 region and a region immediately upstream of the -35 region of the sigma(70) promoter of phaP, where two imperfect 12 bp repeat sequences (GCAMMAAWTMMD) were identified on the sense and anti-sense strands. PhaR also binds 86 bp upstream of the phaR translational start codon, where the sigma(54)-dependent promoter was identified. PhaR also binds to the surface of PHA granules. In the cytoplasm of a phaROmegaKm mutant of R. eutropha H16, increased quantities of PhaP were detected and the cells formed by this strain were much smaller and had many more PHA granules present than the wild-type. These data support the following model for the regulation of phaP expression. Under cultivation conditions not permissive for PHA biosynthesis or in mutants defective in PHA biosynthesis, PhaR binds to the phaP promoter region and represses transcription of this gene. After the onset of PHA biosynthesis, under conditions that are permissive for the formation of nascent granules, PhaR binds to PHA granules and phaP is transcribed. At the later stages of PHA accumulation, PhaR no longer binds to the granules and the transcription of phaP is again repressed. In addition to this, phaR expression is subject to autoregulation. Excess PhaR that has not bound to the phaP upstream region or to PHA granules binds to the phaR upstream region, thereby repressing its own transcription.

Production of microbial polyester by fermentation of recombinant microorganisms

Polyhydroxyalkanoates (PHAs) can be produced from renewable sources and are biodegradable with similar material properties and processibility to conventional plastic materials. With recent advances in our understanding of the biochemistry and genetics of PHA biosynthesis and cloning of the PHA biosynthesis genes from a number of different bacteria, many different recombinant bacteria have been developed to improve PHA production for commercial applications. For enhancing PHA synthetic capacity, homologous or heterologous expression of the PHA biosynthetic enzymes has been attempted. Several genes that allow utilization of various substrates were transformed into PHA producers, or non-PHA producers utilizing inexpensive carbon substrate were transformed with the PHA biosynthesis genes. Novel PHAs have been synthesized by introducing a new PHA biosynthesis pathway or a new PHA synthase gene. In this article, recent advances in the production of PHA by recombinant bacteria are described.

Properties, modifications and applications of biopolyesters

Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate) (PHB) is the most common, can be accumulated by a large number of bacteria as energy and carbon reserve. Due to their biodegradability and biocompatibility these optically active biopolyesters may find industrial applications. A general overview of the physical and material properties of PHAs, alongside with accomplished applications and new developments in this field is presented in this chapter. The properties of PHAs are dependent on their monomer composition and therefore it is of great interest that recent research has revealed that, in addition to PHB, a large variety of PHAs can be synthesized microbially. The monomer composition of PHAs depends on the nature of the carbon source and microorganism used. PHB is a typical highly crystalline thermoplastic whereas medium chain length PHAs are elastomers with low melting points and a relatively lower degree of crystallinity. By (chemical) modification of the PHAs, the ultimate properties of the materials can be adjusted even further, when necessary. Applications that have been developed from PHB and related materials (e.g. Biopol) can be found in very different application areas and cover packaging, hygienic, agricultural and biomedical products. Recent application developments based on medium chain length PHAs range from high solid alkyd-like paints to pressure sensitive adhesives, biodegradable cheese coatings and biodegradable rubbers. Technically, the prospects for PHAs are very promising. When the price of these materials can be further reduced, application of biopolyesters will also become economically very attractive.

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 containing sulfur in the backbone. The Gram-negative polyhydroxyalkanoate (PHA)-accumulating bacterium Ralstonia eutropha synthesized a copolymer of 3-hydroxybutyrate and 3-mercaptopropionate, poly(3HB-co-3MP), when 3-mercaptopropionic acid or 3,3'-thiodipropionic acid was provided as carbon source in addition 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 PHAs. Depending on the cultivation conditions and the feeding regime, poly(3HB-co-3MP) contributed up to 19% of the cellular dry weight, with a molar fraction of 3MP of up to 43%. The chemical structure of poly(3HB-co-3MP) was confirmed by GC/MS, IR spectroscopy, (1)H- and (13)C-NMR spectroscopy, and elemental sulfur analysis. The identification of this novel biopolymer reveals a new quality regarding the substrate range of PHA synthases and their capability for the synthesis of technically interesting polymers.

Biochemical and genetic analysis of PHA synthases and other proteins required for PHA synthesis

Polyhydroxyalkanoic acids (PHA) represent a complex class of storage polyesters that are synthesized by a wide range of different gram-positive and gram-negative bacteria as well as by some Archaea and that are deposited as insoluble cytoplasmic inclusions. PHA synthases, which are the key enzymes for PHA biosynthesis, have been characterized in much detail. At present 42 PHA synthase structural genes from 38 different bacteria have been cloned, and from 30 genes the nucleotide sequences were obtained. The strategies successfully employed to clone these genes and the current knowledge on the organization of the PHA synthase genes and other genes encoding proteins related to PHA metabolism will be compiled. In addition, the primary structures of the 30 PHA synthases were aligned and analyzed with respect to highly conserved amino acids and biochemical features. The direction, in which research should proceed, in order to increase our knowledge on biosynthesis of PHAs and to utilize this knowledge for the development of technically and economically feasible processes for the production of these polyesters will be outlined.

Bacterial and other biological systems for polyester production

Poly(3-hydroxybutyric acid) and other structurally related aliphatic polyesters from bacteria, referred to as polyhydroxyalkanoic acids, form biodegradable thermoplastics and elastomers that are currently in use, or being considered for use, in industry, medicine, pharmacy and agriculture. At present, they are produced by microbial fermentations; in the future, production will also be possible by in vitro methods or by agriculture using transgenic plants. Representatives from this highly diverse class of polyesters might be produced as commodity chemicals for bulk applications, and others as fine chemicals for special applications.