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

Sherif M El-Kadi,Sahar El-Nahrawy,Hossam F A El-Shaer,Mohssen Elbagory,Adel A Shoukry,Alaa El-Dein Omara,Hassan A H El-Zawawy,Dina Fathi Ismail Ali

doi:10.3390/polym13213801

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.

Highlights

IntroductionSince petroleum-based plastics have become a major cause of environmental pollution, degradable plastics have attracted a great deal of attention worldwide for their unique properties, such as thermoplasticity
10 bacterial isolates which were isolated on medium (A) were bacilli, Gram positive, spore positive, capsule positive and negative, and motile, and the indole test, catalase test, starch hydrolysis and casein hydrolysis were positive (Table S1, Supplementary Materials)
The results showed that the addition of sugar beet molasses in the medium of A. salinestris increased the cell dry weight (CDW), PHB concentration, PHB% and conversion coefficient

Summary

Introduction

Since petroleum-based plastics have become a major cause of environmental pollution, degradable plastics have attracted a great deal of attention worldwide for their unique properties, such as thermoplasticity. Production of these vital plastics is limited due to their high cost of production. The slow growth of the PHB market since the 1980s is due to the high cost of production for the amount of PHB produced. Only about 1% of plastic materials on the market are biodegradable, and with the increase in environmental pollution, there is a need to increase the production of PHB [2]. PHBs are a class of biopolymers produced by different microbial species. PHBs have advanced applications in the medical sector (surgical pins and sutures, wound dressings, bone replacements), the packaging industry (packaging films, bags, cosmetics containers, shampoo bottles), and agriculture (plastic mulch, as a carrier for long-term doses of herbicides, fungicides and insecticides) [3–6]

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