Degradation and conversion of toxic compounds into useful bioplastics by Cupriavidus sp. CY-1: relative expression of the PhaC gene under phenol and nitrogen stress

Abstract

In this study different types of toxic compounds, i.e., alkylphenols, mono and poly-aromatic hydrocarbons were converted into polyhydroxybutyrate (PHB) using the isolated bacteria Cupriavidus sp. CY-1. The influence of Tween-80 on the toxic compound degradation ability of CY-1 was analyzed using high pressure liquid chromatography. Among all the compounds, CY-1 showed the highest removal of naphthalene (100 ± 6%), followed by phenol (96 ± 7%), and the lowest removal of alkylphenols without Tween-80 addition. However, Tween-80 addition enhanced the degradation capacity of CY-1, and showed the highest removal of 4-tertiary-butylphenol (74 ± 5%), followed by phenol (69 ± 5%), 4-chlorophenol (59 ± 3%), 4-tertiary-octylphenol (53 ± 5%), and naphthalene (48 ± 5%). Further experiments were carried out for conversion of toxic compounds into PHB. CY-1 grown with phenol (48 ± 6%) and naphthalene (42 ± 4%) showed the highest PHB production. The functional groups, structure and thermal properties of the produced PHB were analyzed. In addition the expression of the PhaC gene was quantified at the transcriptional level through real time quantitative PCR. The results showed up-regulation of the PhaC gene in the presence of phenol, and up and down-regulations in the presence of nitrogen. The maximum PhaC transcript expression was 5.37 folds at 100 mg l⁻¹ nitrogen concentration.