Providencia rettgeri and Sporosarcina koreensis as efficient cell factories for valorization of palm oil mill effluent to produce polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are versatile carbon-neutral, eco-friendly biopolymers that can replace highly polluting petroleum plastics. Microorganisms accumulate PHAs in response to stress. Unfortunately, PHA is more expensive than plastics due to high cost of feedstock. Palm Oil Mill Effluent (POME) an abundant waste from oil palm production can support sustainable production of PHA using appropriate microorganism. Fresh and naturally acidified POME were used as negative-cost feedstock to produce PHA using novel bacteria. Six of 247 isolates obtained from POME / dumpsite soil efficiently accumulated between 19 and 72% PHA. Two isolates that accumulated the most polymers were identified as Providencia rettgeri and Sporosarcina koreensis. At optimum yield they accumulated respectively 4.2g/L (72% of 5.8g/L biomass) and 3.4g/L (66% of 5.15g/L biomass) in POME at 72hours. Optimization studies show that pH 6, C:N ratio, 25:1, titratable acidity, 0.39% for both isolates, and inoculum size, 10% v/v for Providencia rettgeri and 5% v/v for Sporosarcina koreensis gave maximum concentration of PHA at 72hours. Fourier transform infrared spectroscopy (FT-IR) and GC-MS analysis of the polymer accumulated by both isolates identified the products as a poly-hydroxyl-butyrate (PHB). This work is reporting for the first time the use of P. rettgeri and S. koreensis in sustainable processes to valorize major agricultural pollutant to value-added high-cost biochemical. The yield of PHA by these isolates on POME feedstock is promising enough to serve as basis for sustainable industrial process. The waste effluent is reduced for COD and pollution potential and may safely be discharged to environment.