Abstract

Polyhydroxyalkanoates (PHAs) are a common family of biodegradable plastics that are used to create a variety of bulk-commodity plastics. Polyhydroxybutyrate (PHB) belongs to the PHA family of bioplastics and is the most widely studied PHA member. As presence of biodegradable plastics, such as PHB, become more prevalent in everyday products, it is of increasing interest to understand how these plastics are being degraded in the natural environment. Pseudomonas aeruginosa is a ubiquitous soil bacterium that exhibits the ability to degrade PHB and use the monomer of this polymer, R-3-hydroxybutyrate (R-3-HB), as a carbon source. P. aeruginosa converts R-3-HB into acetoacetate through the enzymatic action of the cytosolic protein beta-3-hydroxybutyrate dehydrogenase (BdhA). Although BdhA from P. aeruginosa has been well characterized, little is known regarding the regulation of this metabolic pathway. Using mutant strains of P. aeruginosa PAO1 lacking the function of the bdhA, PA2004, and PA2005 genes, complementation assays were performed to determine the role of these genes in R-3-HB metabolism. The experimental results indicate that the PA2004 gene codes for a putative R-3-HB transporter and the PA2005 gene encodes an enhancer binding protein (EBP) that regulates expression of the bdhA-PA2004 gene operon. Determination of the DNA binding region of the putative PA2005 EBP was further established by performing electrophoretic mobility shift assays using the region of the P. aeruginosa gene upstream of the PA2004-bdhA operon promoter. The results of these experiments have provided insight into the genetic and metabolic processes responsible for R-3-HB degradation by P. aeruginosa.