The polyhydroxyalkanoate (PHA) synthase 1 of Pseudomonas sp. H9 synthesized a 3-hydroxybutyrate-dominant hybrid of short- and medium-chain-length PHA.

Pseudomonas sp. H9 (H9), an environmental strain isolated from a riverbank soil sample collected in southern Taiwan, is Gram-negative and shares a 99 % sequence identity to Pseudomonas putida KT2440 based on 16S rRNA gene analysis. H9 produced novel polyhydroxyalkanoates (PHA) including a hybrid PHA, comprised of 3-hydroxyvalerate (37 mol%) and medium-chain-length (MCL) monomers from valerate, as well as a 3-hydroxyhexanoate-dominant (93 mol%) MCL-PHA from hexanoate. Next-generation sequencing analysis showed H9 had a typical class II PHA operon, consisted of phaC1H9-phaZH9-phaC2H9, in which phaC1H9 was the sole active PHA synthase in H9. Deletion of phaC1H9 gene led to a complete loss of its PHA accumulation capability. Knockout of phaC2H9 gene, in contrast, affected neither bacterial growth nor PHA accumulation. When co-expressed with the phaAB genes of Ralstonia eutropha H16 in the PHA mutant strain Pseudomonas sp. H9ΔC1, phaC1H9 synthesized a hybrid PHA consisted of 3-hydroxybutyrate (3HB) (75 mol%) and MCL-monomers, confirmed in analyses using hot-acetone fractionation and 13C-NMR spectroscopy. As a novel PHA synthase, PhaC1H9 possesses a broad substrate specificity to synthesize a hybrid of SCL- and MCL-PHA, known to have many mechanical properties for potential applications.

Cultivation temperature modulated the monomer composition and polymer properties of polyhydroxyalkanoate synthesized by Cupriavidus sp. L7L from levulinate as sole carbon source.

Cupriavidus sp. L7L, a newly isolated wild-type soil bacterium, was found to synthesize polyhydroxyalkanoate (PHA) terpolymers from levulinic acid (LA), a top bio-based platform chemical, as the sole carbon source. NMR spectra showed that the terpolymers consisted mainly of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and a small amount (2.1-4.8 mol%) of 4-hydroxyvalerate (4HV). The combination of monomers together with high molecular weights improved markedly the thermal and mechanical properties of the terpolymers. Increasing cultivation temperature of Cupriavidus sp. L7L increased the proportions of 3HB and decreased the proportions of 3HV. A fed-batch fermentation using LA as the sole carbon source without pH control produced a biomass of 15.8 dry weight g L-1 that contained 81 dry weight% of a terpolymer P(3HB-co-33.7 mol% 3HV-co-2.1 mol% 4HV), equaling a productivity of 0.213 g PHA L-1 h-1. The terpolymer showed a melting point of 92 °C and elongation at break of 630%, compared to 84.6 °C and 462%, respectively, for the copolymer P(3HB-co-35.9 mol% 3HV) that contained no 4HV. This study showed that Cupriavidus sp. L7L exhibited a great potential for producing PHA polymers with excellent mechanical property that could be modulated by cultivation temperature when cultivated exclusively in LA.

Planctobacterium marinum gen. nov., sp. nov., a new member of the family Alteromonadaceae isolated from seawater.

A bacterial strain designated K7T was isolated from the South China Sea and characterized using a polyphasic taxonomic approach. Cells of strain K7T were Gram-stain-negative, aerobic, poly-ß-hydroxybutyrate-accumulating, motile by means of a monopolar flagellum, non-spore forming rods surrounded by a thick capsule and forming yellow colonies. Growth occurred at 4-35 °C (optimum, 25-30 °C), at pH 5.0-9.0 (optimum, pH 7.0) and with 0.5-10 % (w/v) NaCl [optimum, 1-4 % (w/v)]. The predominant fatty acids were summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c), C16 : 0 and C18 : 1ω7c. The major isoprenoid quinone was Q-8 and the DNA G+C content was 46.5 mol%. The polar lipid profile consisted of a mixture of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine, one uncharacterized phospholipid, two uncharacterized aminophospholipids and five uncharacterized lipids. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain K7T formed a distinct lineage with respect to closely related genera in the family Alteromonadaceae. Strain K7T was most closely related to Aestuariibacter, Aliiglaciecola, Paraglaciecola and Glaciecola, and the levels of 16S rRNA gene sequence similarity with respect to the type species of related genera were less than 95 %. On the basis of the genotypic and phenotypic data, strain K7T represents a novel species of a new genus of the family Alteromonadaceae, for which the name Planctobacterium marinum gen. nov., sp. nov. is proposed. The type strain of Planctobacterium marinum is K7T (=BCRC 80901T=LMG 28835T=KCTC 42657T).

Isolation and characterization of the unicellular diazotrophic cyanobacterium Group C TW3 from the tropical western Pacific Ocean.

A unicellular diazotrophic cyanobacterium strain of Group C, designated TW3, was isolated from the oligotrophic Kuroshio Current of the western Pacific Ocean. To our knowledge, this represents the first successful laboratory culture of a Group C unicellular diazotroph from oceanic water. TW3 cells are green rods, 2.5-3.0 µm in width and 4.0-6.0 µm in length. Phylogenetic analyses of both 16S rRNA and nifH gene fragments indicated that the TW3 sequences were over 98% identical to those of the previously isolated Cyanothece sp. ATCC51142 and Gloeocapsa sp., suggesting that TW3 is a member of the Group C unicellular diazotrophs. In addition, both TW3 and Cyanothece sp. ATCC51142 share morphological characteristics; both strains are sheathless and rod-shaped, display binary fission in a single plane, and possess dispersed thylakoids. TW3 grows aerobically in nitrogen-deficient artificial seawater, and exhibited the highest observed growth rate of 0.035 h(-1) when cultured at 30°C and 140 µmol m(-2) s(-1) of light intensity. The nitrogen fixation rate, when grown optimally using a 12 h/12 h light-dark cycle, was 7.31 × 10(-15) mol N cell(-1) day(-1) . Immunocytochemical staining using Trichodesmium sp. NIBB1067 nitrogenase antiserum revealed the existence of diazotrophic cells sharing morphological characteristics of TW3 in the Kuroshio water from which TW3 was isolated.