Department of Agronomy Food Natural Resources Animals and Environment (DAFNAE), Università di Padova, Viale dell'Università 16, 35020 Legnaro (Pd), Italy.
N Biotechnol. 2013 Sep 25;30(6):629-34. doi: 10.1016/j.nbt.2012.11.019. Epub 2012 Nov 29.
In the present paper we report the exclusive microbial preparation of polyhydroxyalkanoates (PHA) containing 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV) and 4-hydroxybutyrate (4HB) as comonomers through the use of unexpensive carbon sources such as whey from dairy industry. Polymers were produced by growing H. pseudoflava DSM 1034 in minimal medium supplemented with sucrose, lactose or whey without any co-substrate added. The chemical and physical properties of the polymers were fully characterized by GPC, DSC, TGA analyses and the composition by GC and (1)H NMR examinations to especially confirm the content of different monomeric units. The presence of 4HB units into PHA samples is particularly aimed in thermoplastic applications where greater flexibility is required and conventional rigid PHAs tend to fail. Usually the insertion of 4HB into chain backbone consisting of 3-hydroxyalkanoates requires expensive carbon sources mostly of petrochemical origin. According to our study the production of P(3HB-co-3HV-co-4HB) terpolymer can be obtained directly by the use of lactose or waste raw materials such as cheese whey as carbon sources. Although the amount of 4HB in the produced terpolymers was usually low and not exceeding 10% of the total molar composition, a PHA containing 18.4% of 4HB units was produced in 1 step fermentation process from this structurally unrelated carbon sources. The crystallinity of the terpolymer is basically to be markedly affected with respect to that of conventional PHAs, thus obtaining a comparatively less rigid material and easier to be processed.
在本论文中，我们报道了通过使用诸如乳制品工业乳清等廉价碳源，以3-羟基丁酸（3HB）、3-羟基戊酸（3HV）和4-羟基丁酸（4HB）作为共聚单体，独家微生物制备聚羟基脂肪酸酯（PHA）。聚合物是通过在补充有蔗糖、乳糖或乳清的基本培养基中培养假黄杆菌DSM 1034而产生的，且未添加任何共底物。通过凝胶渗透色谱（GPC）、差示扫描量热法（DSC）、热重分析（TGA）分析对聚合物的化学和物理性质进行了全面表征，并通过气相色谱（GC）和核磁共振氢谱（¹H NMR）检测确定了其组成，以特别确认不同单体单元的含量。在需要更大柔韧性且传统刚性PHA往往失效的热塑性应用中，PHA样品中4HB单元的存在尤为重要。通常，将4HB插入由3-羟基链烷酸酯组成的链主链中需要大多源自石化的昂贵碳源。根据我们的研究，使用乳糖或奶酪乳清等废弃原料作为碳源可直接获得聚（3HB-co-3HV-co-4HB）三元共聚物。尽管所生产三元共聚物中4HB的含量通常较低，不超过总摩尔组成的10%，但通过一步发酵过程从这种结构不相关的碳源中制备出了含有18.4% 4HB单元的PHA。与传统PHA相比，三元共聚物的结晶度基本会受到显著影响，从而得到一种刚性相对较小且更易于加工的材料。
