Polyhydroxybutyrate accumulation by a cadmium-resistant strain of Cupriavidus taiwanensis

• Cupriavidus taiwanensis EJ02 was isolated from contaminated sediments.
• C. taiwanensis EJ02 could tolerate high concentration of cadmium.
• PHB accumulation in C. taiwanensis EJ02 was significant.
• PHB production by C. taiwanensis EJ02 under heavy metal stress was evaluated.

Polyhydroxybutyrate (PHB) is usually produced in various microorganisms in response to the environmental conditions of physiological stress. Cupriavidus taiwanensis is known to accumulate significant amounts of PHB and is phylogenetically related to Ralstonia eutropha (Cupriavidus necator), which is also well known for producing PHB. In this study, an environmental isolate of C. taiwanensis resistant to heavy metals (strain EJ02) was evaluated for its ability to accumulate PHB when grown in the presence of cadmium ions. C. taiwanensis EJ02 tolerated much higher concentrations of cadmium (up to 5 mM) when grown in complex (Luria-Bertani) media compared to C. taiwanensis strains BCRC 17206T and BCRC 17208 (1 mM). The growth of the strain EJ02 showed more resistance to cadmium (up to 7 mM) when grown in LB medium containing sodium gluconate than that in LB only. There was no significant effect on cadmium resistance for C. taiwanensis BCRC 17206T and BCRC 17208 when sodium gluconate was supplemented in LB medium. Although the production of PHB by C. taiwanensis EJ02 is enhanced by the presence of cadmium, the mRNA expression of the key genes for PHB biosynthesis (i.e., phaCAB) is lower than in the EJ02 cells not exposed to cadmium determined by real-time PCR analysis. The tolerance of C. taiwanensis EJ02 to the presence of heavy metals might be associated with its ability to accumulate PHB and to adapt to the stress of an environment with heavy metals.