Biodegradable Latexes from Animal-Derived Waste: Biosynthesis and Characterization of mcl-PHA accumulated by Ps. citronellolis

Background

mcl-PHA biosynthesis by Pseudomonas citronellolis from tallow-based biodiesel as inexpensive carbon feed stock was accomplished. Fermentation protocols, kinetic analysis, an efficient product recovery strategy, and a detailed product characterization are presented.
Results

A maximum specific growth rate, μmax. of 0.10 and 0.08 h−1, respectively, was achieved in two different fermentation set-ups. Volumetric productivity for mcl-PHA amounted to 0.036 g/L h and 0.050 g/L h, final intracellular PHA contents calculated from the sum of active biomass and PHA to 20.1 and 26.6 wt.%, respectively. GC-FID analysis showed that the obtained biopolyester predominantly consists of 3-hydroxyoctanoate and 3-hydroxydecanoate, and, to a minor extent, 3-hydroxydodecanoate, 3-hydroxynonanoate, 3-hydroxyhexanoate, and 3-hydroxyheptanoate monomers. This was confirmed by 1H- and 13C NMR, also evidencing the occurrence of low quantities of unsaturated and 3-hydroxyvalerate building blocks. High purity of the recovered materials was proofed by elemental analysis. Regarding the results from thermogravimetric analysis, differential scanning calorimetry and molecular mass determination, results were in a range typical for this type of PHA (1st fermentation: decomposition temperature Td = 296 °C, peak of melting range Tm = 48.6 °C; glass transition temperature Tg = −46.9 °C, degree of crystallinity Xc = 12.3%, Mw = 66,000, Mn = 35,000, dispersity index Pi = 1.9; 2nd fermentation: Td = 295 °C, Tm = 53.6 °C, Tg = -43.5 °C, Xc = 10.4%, Mw = 78,000, Mn = 196,000, Pi = 2.5).