Characterization of Polyhydroxyalkanoates Produced by Rhodobacter sphaeroides ADZ101

Abstract

Background: Polyhdroxyalkanoate (PHA) is a biopolymer synthesized by some bacteria as a carbon and energy storage. It has similar characteristics to fossil-derived plastic. Hence, it is considered a replacement for nonbiodegradable plastic. However, the bacterial strain and culture conditions determine the biosynthesis and properties of PHA. Objective: To determine the structure and properties of PHA produced by Rhodobacter sphaeroides ADZ101. Methods: Fourier Transform Infrared spectroscopy (FTIR) was used to evaluate the functional groups of the PHA, thermal stability analysis was carried out using TGA, and molecular weight was determined with MALDI-TOF MS. Other structural analyses were performed using NMR and GC-MS. Results: The results showed the presence of absorption bands related to the symmetrical CH3 group, carbonyl ester, bacterial intracellular protein amide, and the stretching vibration in the amorphous phase. Structural analysis revealed that the PHA contains short- and medium-length monomers in the order C5, C13, C14, to C18. The GCMS analysis showed that the PHA consisted of poly 3-hydroxybutyrate and poly 3-hydroxyvalerate with the presence of methyl esters of dodecanone, butyrate, hexadeconoic and heptadeconoic acids, and phenol 2,5 bis (1,1 dimethyl ethyl)-4-phenol. The estimated molecular weight of the polymer was 628.55 kDa. Thermal analysis revealed that the maximum PHA decomposition temperatures are 395 and 454°C, indicating two major decomposition reactions. Conclusion: The PHA produced by R. sphaeroides ADZ101 exhibit enhanced temperature decomposition and has numerous potential industrial applications.