Production of polyhydroxybutyrate (PHB), a biodegradable polymer from seaweed biomass using novel bacterial isolates

Poly-(3-hydroxybutyrate) (PHB), is a partially crystalline polymer naturally synthesized by microorganisms, and the production of PHB has attracted much attention recently due to its exceptional biodegradable and biocompatible nature. By serving as a copolymer and by being a block copolymer, PHB enhances the mechanical properties of the polymer materials. The materials developed using PHB as a block copolymer are used in numerous applications such as polymer aging resistance, controlled drug delivery, cardiovascular engineering, thin film formation, etc. This study focuses on synthesizing PHB from microbial sources as cell factories. From distinct natural sources two novel bacterial isolates, Bacillus pacificus NAA2 (NAA2) and Klebsiella quasipneumonia NAA4 (NAA4) were screened based on their high PHB synthesizing abilities. To improve the PHB levels, a series of process optimization studies were conducted. The process conditions such as different carbon and nitrogen sources, concentrations, pH levels, temperatures, and incubation periods have been explored and optimized. Under optimized conditions, NAA2 produced 2.92 g/L of PHB (79 %) with glycerol and peptone as carbon and nitrogen sources respectively at pH 7.5 and 35 degree celsius at 48 h. The other isolate, NAA4, produced 2.89 g/L of PHB (73 %) from xylose and urea as equivalent carbon and nitrogen sources respectively with the same pH and temperature after 36 h of incubation. In addition, the replacement of conventional carbohydrates (glucose and/ or xylose) with seaweed hydrolysate exhibited almost equivalent levels of PHB 72.7 and 70.7 % of PHB in NAA2 and NAA4 respectively. Fourier Transform Infrared (FTIR) spectroscopy and FE-SEM analysis confirmed the production of a polymer. Though there are several studies reported with other Bacillus sp and Klebsiella sp., this is the only study that used novel strains Bacillus pacificus (NAA2) and Klebsiella quasipneumonia (NAA4) as the microbial cell factories for the effective synthesis of PHB using seaweed as a substrate. Thus, the technology for bioconversion of harmful and waste seaweed biomass into PHB with dual sustainability was developed.