*Article* **Biosynthesis of Poly-ß-Hydroxybutyrate (PHB) from Different Bacterial Strains Grown on Alternative Cheap Carbon Sources**

**Sherif M. El-Kadi <sup>1</sup> , Mohssen Elbagory 2,3 , Hassan A. H. EL-Zawawy 4, Hossam F. A. EL-Shaer 5, Adel A. Shoukry 4, Sahar El-Nahrawy 3, Alaa El-Dein Omara 3,\* and Dina Fathi Ismail Ali <sup>6</sup>**


**Abstract:** Thirty bacterial isolates were tested on three different media for Poly-ß-hydroxybutyrate (PHB) production. The best bacterial isolates for producing PHB were screened and identified based on molecular biology; then, using three different alternative carbon sources (dried whey, sugar beet molasses and date molasses), physical properties were evaluated by Infrared (IR) spectrometry and Gas chromatography–mass spectrometry (GC-MS/MS) analysis. Our results showed that the best isolates identified based on molecular biology were *Bacillus paramycoides* MCCC 1A04098, *Azotobacter salinestris* NBRC 102611 and *Brevundimonas naejangsanensis* BIO-TAS2-2. The addition of sugar beet molasses to the medium of *A. salinestris* increased the cell dry weight (CDW), PHB concentration, PHB% and conversion coefficient (4.97 g/L, 1.56 g/L, 31.38% and 23.92%, respectively). The correlation coefficient values between PHB g/L and CDW g/L varied between very strong and moderate positive correlation. IR of the produced PHB from *B. paramycoides* and *A. salinestris* showed similar bands which confirmed the presence of PHB; however, *B. naejangsanensis* showed weak bands, indicating lower PHB concentration. The chemical composition obtained showed that the GC-MS of the PHB extracted represents 2, 4-ditert-butylphenol for *B. paramycoides* and isopropyl ester of 2 butenoic acid for both of *A. salinestris* and *Brevundimonas naejangsanensis*. Therefore, PHB produced by microorganisms can be considered a biodegradable polyester, and represents a promising technique for the development of eco-friendly and fully biodegradable plastics.

**Keywords:** agro-industrial waste; GC-MS/MS spectrometry; IR spectrometry; PHB
