Isolation and characterization of two novel polyhydroxybutyrate (PHB)-producing bacteria

Abstract

Bioplastics are naturally occurring biodegradable polymers made from polyhydroxyalkanoates (PHA) of which poly 3-hydroxy butyric acid (PHB) is the most common. PHB serves as an energy storage molecule and accumulates intracellularly as storage granules in microbes. This work utilized the biodiversity of bacteria to isolate various species from different environments and screen them for their ability to produce PHB. Sixteen unknown samples were collected, assayed and compared with known bioplastic producers (Ralstonia, Bacillus and Pseudomonas). These species were identified by 16S rRNA sequencing. Conditions were extensively optimized by varying the temperature, carbon, nitrogen and substrate sources for maximal PHB production. Presence of accumulation of PHB in these strains was confirmed by microscopic staining. This is the first report to experimentally demonstrate the synthesis of PHB by two novel species, Rahnella aquatilis and Stenotrophomonas maltophilia. R. aquatilis was collected from a children’s plastic toy, while S. maltophilia was collected from the sand of a local beach. The phenotypic profiles of these two species were subsequently studied using phenotype microarray panels which allowed the testing of the effect of more than 90 different carbon, nitrogen, sulfur and phosphorus sources as well as pH on the growth characteristics of these strains.

Key words: Poly 3-hydroxy butyric acid (PHB), polyhydroxybutyrate, bioplastics, phenotype microarray, Rahnella, Stenotrophomonas.