Production of Polyhydroxyalkanoates (pha) by bacillus and pseudomonas on Cheap Carbon Substrates

Abstract

Polyhydroxyalkanoates are renewable, and biocompatible plastics having physiochemical properties similar to petrochemical plastics, and meet the Sustainable Development Goals (SDG). Two bacterial strains: Pseudomonas aeruginosa and Bacillus subtilis were selected to produce the PHA. The standard carbon source was glucose while molasses and banana peels were cheaper carbon substrates used in a medium to grow the bacterial strains. Sudan black B and Nile blue A staining were used to confirm the PHA production via spread plate assay. PHA granules were observed inside the bacterial cell microscopically, using Sudan stain. The carbohydrate concentration was estimated in molasses (29.4mg/mL) and banana peel extract (9.8mg/mL) by the Phenol-sulfuric acid test. In batch fermentation, time profiles of PHA production and growth of microbial strains for every 3hrs were performed up to incubation of 48hrs at 150rpm. PHA was extracted by sodium dodecyl sulfate digestion and chloroform extraction method. PHA production in Pseudomonas aeruginosa was 1.120g/L (66.82%) and 0.380g/L (44.60%) while in Bacillus subtilis was 0.476g/L (53.84%) and 0.288g/L (39.18%) utilizing molasses and banana peels, respectively after 48hrs. FTIR characterized the PHA monomer as polyhydroxybutyrate having a C=O bond at 1697.8cm^-1 and 1750.0cm^-1 and a CH₃ group at 1395.9cm^-1 and 1458.3cm^-1. A statistical significance between the PHA productions was calculated by applying an unpaired t-test, for Pseudomonas aeruginosa, a significant difference was observed between glucose with both substrates, while for Bacillus subtilis, a significant difference was noted only between glucose and peel extract.

Keywords:
Bacillus ; Banana peels; Molasses; PHA yield; Pseudomonas

HIGHLIGHTS

• Compared agro-industrial wastes i.e. molasses and banana peels.

• Highest amount of PHA was produced by Pseudomonas aeruginosa utilizing molasses.

• Statistically, a significant difference was observed between cheaper substrates.

• FTIR analysis confirmed the extracted monomers as PHB.

GRAPHICAL ABSTRACT