Bio-products

OTHER BIO-PRODUCTS

BIODEGRADABLE POLYMERS—MICROBIAL SYNTHESIS OF POLYMERS

Researcher: Jim Kastner, jkastner@engr.uga.edu

Biodegradable polymers are an alternative to traditional petrolium based polymers and would help to reduce solid waste disposal problems associated with most plastics.

Due to disposal concerns, plastic production costs will increasingly be influenced by environmental legislation. Thus, environmental pressures are forcing polymer manufacturers to consider biodegradable polymers as an alternative. Biodegradable polymers would help to reduce solid waste disposal problems associated with most plastics. Plastics produced from bacteria are a potential source of biodegradable polymers. Poly-b-Hydroxybutyric acid (PHB) and poly-b-hydroxyalkanoic acids (PHA), biodegradable thermoplastics, can be produced from a wide range of substrates using bacteria. These biodegradable thermoplastics can be used as packaging material and can be utilized as drug delivery systems, since these polymers are immunologically inert.

Several factors influence the economics of biodegradable polymer production. One factor is the cost of the substrate. The ability to produce biodegradable polymers from inexpensive and renewable carbon sources, such as xylose and lactose, may help to improve the economics of the process. Xylose is a five carbon sugar which can be generated from the hemicellulose of agricultural and forest residues. Recent estimates indicate that approximately 435 million dry tons of agricultural and forestry residues are produced per year. Lactose is a disaccharide which is generated in large volumes from cheese whey. About 28 billion pounds of liquid cheese whey is currently wasted in the U.S.

In our research, poly-b-Hydroxybutyric acid was produced from the renewable and inexpensive carbon sources, xylose and lactose, using Pseudomonas cepacia. The average maximum specific growth rate on D-glucose and xylose was approximately 0.32 hr-1 compared to 0.10 hr-1 on lactose. P. cepacia was shown to accumulate a maximum of 0.48 g of PHB per g of dry biomass if grown on D-glucose, 0.49 g of PHB per g of dry biomass if grown on xylose, and 0.56 g of PHB per g of dry biomass if grown on lactose. The maximum PHB yield was found to be 0.145 g/g from glucose, 0.107 g/g from xylose and 0.147 g/g from lactose. The maximum weight average molecular weight Mw for PHB extracted from glucose grown cells was 498,664 with a polydispersivity of 2.3, and 595,086 Mw with a polydispersivity of 2.47 for PHB extracted from xylose grown cells. The maximum Mw of PHB produced from lactose was 873,178 with a polydispersivity of 2.15. This is the first report of PHB production from lactose using a bacteria which had not been genetically engineered to metabolize lactose. These studies demonstrated that P. cepacia may have the potential to produce biodegradable thermoplastics, from hemicellulosic hydrolyzates and cheese whey.