Quorum sensing inhibitors as antipathogens: biotechnological applications

The mechanisms through which microbes communicate using signal molecules has inspired a great deal of research. Microbes use this exchange of information, known as quorum sensing (QS), to initiate and perpetuate infectious diseases in eukaryotic organisms, evading the eukaryotic defense system by multiplying and expressing their pathogenicity through QS regulation. The major issue to arise from such networks is increased bacterial resistance to antibiotics, resulting from QS-dependent mediation of the formation of biofilm, the induction of efflux pumps, and the production of antibiotics. QS inhibitors (QSIs) of diverse origins have been shown to act as potential antipathogens. In this review, we focus on the use of QSIs to counter diseases in humans as well as plants and animals of economic importance. We also discuss the challenges encountered in the potential applications of QSIs.     

Metabolic flux modeling of detoxification of acetic acid by Ralstonia eutropha at slightly alkaline pH levels

Ralstonia eutropha grows on and produces polyhydroxyalkanoates (PHAs) from fermentation acids. Acetic acid, one major organic acid from acidogenesis of organic wastes, has an inhibitory effect on the bacterium at slightly alkaline pH (6 g HAc/L at pH 8). The tolerance of R. eutropha to acetate, however, was increased significantly up to 15 g/L at the slightly alkaline pH level with high cell mass concentration. A metabolic cell model with five fluxes is proposed to depict the detoxification mechanism including mass transfer and acetyl-CoA formation of acetic acid and the formation of three final metabolic products, polyhydroxybutyrate (PHB), active biomass, and CO(2). The fluxes were measured under different conditions such as cell mass concentration, acetic acid concentration, and medium composition. The experimental results indicate that the acetate detoxification by high cell mass concentration is attributed to the increased fluxes at high extracellular acetate concentrations. The fluxes could be doubled to reduce and hence detoxify the accumulated intracellular acetate anions.     

微生物合成中链聚羟基烷酸酯研究进展

某些微生物细胞在特定营养限制的条件下会产生聚羟基烷酸酯作为碳源储备。和短链聚羟基烷酸酯(PHB)一样 ,中链聚羟基烷酸酯由于具有更优良的性能、更高的附加值和更广泛的用途而受到人们的关注 ;此外 ,中链聚羟基烷酸酯还可以被人工合成为具有功能性侧链的半合成高聚物 ,并因此能够具有更好的弹性和更理想的结晶性能等优点 ,从而成为近年来对环境友好的生物可降解材料的研究重点。在能够合成中链聚羟基烷酸酯的微生物中 ,食油假单胞菌是最典型 ,也是研究得最多的一种。本文对由食油假单胞菌合成中链聚羟基烷酸酯的特点、代谢机制、发挥过程等内容进行了综述 ,并提出了这一研究领域未来可能的研究方向     

En route to economical eco‐friendly solvent system in enhancing sustainable recovery of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) copolymer

Separation of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐co‐4HB)] from bacterial cell matter is a critical step in the downstream process with respect to material quality and eco‐balance as P(3HB‐co‐4HB) is widely used for biomedical applications. Therefore, an efficient and eco‐based extraction of P(3HB‐co‐4HB) using a combination of NaOH and Lysol in digesting the non‐polymeric cell material (NPCM) digestion is developed. The NaOH and Lysol show synergistic influence on the copolymer extraction at a high purity and recovery of 97 and 98 wt% respectively. The optimized cell digestion method was found applicable to a vast batch of cells containing copolymers from various 4HB monomer compositions. At the largest extraction volume of 100 L, P(3HB‐co‐4HB) with a purity of 89 wt% was extracted with a maximum recovery of 90 wt%. The method developed has also eliminated the cell pretreatment step. The extraction method developed in this research has not only produced an economic and efficient copolymer recovery but has also retained the copolymer quality, in term of its molecular weight and thermal properties. It demonstrates a practical and promising downstream processing method in recovering the copolymer effectively from the bacterial biomass.     

Role of nitrate in biological phosphorus removal in a sequencing batch reactor

Summary The effects of nitrate on phosphorus release and uptake in a sequencing batch reactor for biological phosphorus removal was investigated. The addition of nitrate decreased phosphorus release in the anaerobic stage. The synthesis of poly(hydroxyalkanoates) was decreased with the presence of nitrate, possibly due to the competitive utilization of the carbon source by PHA synthesis and denitrification of nitrate. Instead of oxygen, nitrate could be used as an electron acceptor for phosphorus removal. However, the simultaneous addition of nitrate and acetate greatly reduced the phosphorus removal rate. Phosphate and nitrate could be removed simultaneously with nitrate as the electron acceptor, and the continuous and steady feeding of nitrate was beneficial to phosphate removal.     

Improvement on the yield of polyhydroxyalkanotes production from cheese whey by a recombinant Escherichia coli strain using the proton suicide methodology

In this work Escherichia coli strain CML3-1 was engineered through the insertion of Cupriavidus necator P(3HB)-synthesis genes, fused to a lactose-inducible promoter, into the chromosome, via transposition-mediated mechanism. It was shown that polyhydroxyalkanotes (PHAs) production by this strain, using cheese whey, was low due to a significant organic acids (OA) synthesis. The proton suicide method was used as a strategy to obtain an E. coli mutant strain with a reduced OA-producing capacity, aiming at driving bacterial metabolism toward PHAs synthesis.Thirteen E. coli mutant strains were obtained and tested in shake flask assays, using either rich or defined media supplemented with lactose. P8-X8 was selected as the best candidate strain for bioreactor fed-batch tests using cheese whey as the sole carbon source. Although cell growth was considerably slower for this mutant strain, a lower yield of OA on substrate (0.04 Cmol_OA/Cmol_lac) and a higher P(3HB) production (18.88 g_P(3HB)/L) were achieved, comparing to the original recombinant strain (0.11 Cmol_OA/Cmol_lac and 7.8 g_P(3HB)/L, respectively). This methodology showed to be effective on the reduction of OA yield by consequently improving the P(3HB) yield on lactose (0.28 Cmol_P(3HB)/Cmol_lac vs 0.10 Cmol_P(3HB)/Cmol_lac of the original strain).     

Polyhydroxyalkanoates: Properties and chemical modification approaches for their functionalization

Polyhydroxyalkanoates (PHAs) have become an attractive biomaterial in research in the past few years due to their extensive potential industrial applications. Being long chain hydroxyl fatty acid molecules, the PHAs are hydrophobic in nature, and have less functional groups. These features limit their applications in various areas. To enhance their usage, these polymers may need to be modified including surface and chemical modifications. Such modifications may alter their mechanical properties, surface structure, amphiphilic character and rate of degradation to fulfil the requirements for their future applications. Chemical modifications allow incorporation of functional groups to PHAs that could not be introduced through biotechnological methods. These chemically reformed PHAs, with enhanced properties, could be used for broad range of applications. This review aims to introduce different chemical modification approaches including some recent methods that had not been explored or discussed so far for PHAs as possible technologies for widening the range of product and application potentials. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:29–41, 2018     

Biosynthesis of medium chain length poly(3-hydroxyalkanoates) (mcl PHAs) from cosmetic co-products by Pseudomonas raguenesii sp. nov., isolated from Tetiaroa, French Polynesia

A new bacterium, designated as strain TE9 was isolated from a microbial mat in French Polynesia and was studied for its ability to synthesize medium chain length poly-β-hydroxyalkanoates (mcl PHAs) during cultivation on cosmetics co-products. The composition of PHAs was analysed by coupled gas chromatography mass spectroscopy (GC/MS), nuclear magnetic resonance (NMR) and Fourier Transform InfraRed (FTIR) spectroscopy. PHAs were composed of C6–C14 3-hydroxyacids monomers, with a predominance of 3-hydroxyoctanoate (3HO), 3-hydroxydecanoate (3HD) and 3-hydroxydodecanoate (3HDD). Differential scanning calorimetry (DSC) experiments allowed the characterization of elastomeric materials with a melting point T_m near 50 °C, enthalpy of fusion ΔH_m from 27 to 32 J/g, and glass transition temperature T_g of −43 °C. Molecular weights ranged from 175,000 to 358,000 g/mol. On the basis of the phenotypical features and genotypic investigations, strain TE9 was assigned to the Pseudomonas genus and the name of Pseudomonas raguenesii sp. nov. is proposed.     

Molecular characterization and properties of (R)-specific enoyl-CoA hydratases from Pseudomonas aeruginosa: metabolic tools for synthesis of polyhydroxyalkanoates via fatty acid beta-oxidation

The use of (R)-specific enoyl-coenzyme A (CoA) hydratase (PhaJ) provides a powerful tool for polyhydroxyalkanoate (PHA) synthesis from fatty acids or plant oils in recombinant bacteria. PhaJ provides monomer units for PHA synthesis from the fatty acid ß-oxidation cycle. Previously, two phaJ genes (phaJ1_Pa and phaJ2_Pa) were identified in Pseudomonas aeruginosa. This report identifies two new phaJ genes (phaJ3_Pa and phaJ4_Pa) in P. aeruginosa through a genomic database search. The abilities of the four PhaJ_Pa proteins and the (R)-3-hydroxyacyl-acyl carrier protein [(R)-3HA-ACP] dehydrases, FabA_Pa and FabZ_Pa, to supply monomers from enoyl-CoA substrates for PHA synthesis were determined. The presence of either PhaJ1_Pa or PhaJ4_Pa in recombinant Escherichia coli led to the high levels of PHA accumulation (as high as 36–41 wt.% in dry cells) consisting of mainly short- (C4–C6) and medium-chain-length (C6–C10) 3HA units, respectively. Furthermore, detailed characterizations of PhaJ1_Pa and PhaJ4_Pa were performed using purified samples. Kinetic analysis revealed that only PhaJ4_Pa exhibits almost constant maximum reaction rates (V_max) irrespective of the chain length of the substrates. The assay for stereospecific hydration revealed that, unlike PhaJ1_Pa, PhaJ4_Pa has relatively low (R)-specificity. These hydratases may be very useful as monomer-suppliers for the synthesis of designed PHAs in recombinant bacteria.     

The Autotrophic Synthesis of Polyhydroxyalkanoate by Alcaligenes eutrophusin the Presence of Carbon Monoxide

The CO-resistant strain B5786 of the hydrogen-oxidizing bacterium Alcaligenes eutrophuswas found to be able to synthesize polyhydroxyalkanoates (PHAs) under the conditions of growth limitation by nitrogen deficiency (the factor that promotes PHA synthesis) and growth inhibition by carbon monoxide. The gas mixtures that contained from 5 to 20 vol % CO did not inhibit the key enzymes of PHA synthesis–-ketothiolase, acetoacetyl-CoA reductase, hydroxybutyrate dehydrogenase, and PHA synthase. In the presence of CO, cells accumulated up to 70–75 wt % PHA (with respect to the dry biomass) without any noticeable increase in the consumption of the gas substrate. Chromatographic–mass spectrometric analysis showed that the PHA synthesized by A. eutrophusis a copolymer containing more than 99 mol % -hydroxybutyrate and trace amounts of -hydroxyvalerate. The PHA synthesized under the conditions described did not differ from that synthesized by A. eutrophuscells from electrolytic hydrogen.