Production of Poly-β-Hydroxybutyrate (PHB) by bacteria isolated from rhizospheric soils

Polymeric materials like plastic and polyester have wide-spread use in today's industrial society because of their ease of processability and amenability in providing a large variety of cost-effective commodity. However, plastics and synthetic polymers are synthesized from nonrenewable resources like petrochemicals and persist in the environment long after intended use, resulting into problems of solid waste management and global environmental pollution. Therefore, there is a growing interest in developing biodegradable plastics such as polyhydroxybutyrate (PHB), which possess desirable physical and chemical properties similar to conventional synthetic plastics, and are environment friendly as well. In the present study, an attempt was therefore made to isolate efficient PHB producing bacteria from soil collected from the rhizospheric area of eight different crops. A total of 40 different types of bacteria were isolated, out of which 28 were found to be PHB positive, based on the viable colony staining method using Sudan Black B. All the 28 PHB positive isolates were characterized biochemically and subjected to quantitative estimation of PHB production, they were found to exhibit PHB yields in the range of 51.29 and 86.08 mg/ml. The culture medium and growth parameters for all the isolates were optimized for maximum PHB production. Glucose as the carbon and ammonium sulphate as the nitrogen source were found to be the best nutritional sources for maximum PHB production. Maintaining the C/N ratio as 20:1 using the best C and N source, pH of the medium at 7.0, and the temperature at 30 0 C were found to be optimum conditions for obtaining maximum PHB yield. A few (Sa7, Su4, De2, De1, Ch2, Ja1) PHB positive isolates were found to be quite efficient PHB producers, thus, exhibiting a potential for their utilization in commercial PHB production.