Preparation of polyhydroxyalkanoates using <i>Pseudomonas helmanticensis</i> in non-sterile media containing glycerol and sodium dodecyl sulfate

Abstract

Biosynthetically-produced Pseudomonas poly-3-hydroxyalkanoates (PHAs) are a promising substitute for conventional plastics. Costs involved with the production of PHAs can be reduced by optimizing power consumption, which can be achieved using nutrient media without preliminary steam sterilization. Cultivation of Pseudomonas bacteria resistant to sodium dodecyl sulfate (SDS) on SDS-containing non-sterile media yields a biomass consisting predominantly of a PHA producer. SDS plays the role of an antimicrobial agent that inhibits the growth of foreign microorganisms. In this work, an SDS-resistant culture of Pseudomonas helmanticensis and media containing glycerol and SDS were used. The concentrations of carbon (glycerol) and nitrogen sources were optimized using an experiment performed according to a central composite rotatable design. The concentration of substrate C and the C/N ratio between the glycerol and nitrogen content were varied. The dependence of the degree of substrate conversion in PHA on C and C/N was derived in the R programming environment. The constructed model adequately describes the experimental data at a significance level of 0.05 (adequacy variance of the regression equation 4.1×10-2; R2 =0.98). According to the constructed model, the conversion of glycerol to PHA equals 6.9±0.4%. Under optimized conditions (0.61 g/L nitrogen source; 8.4 g/L glycerol; 96 h), P. helmanticensis converts 7.0% of the substrate to PHA with an average monomer unit length. Using a 16S rRNA metagenomic assay, the proportion of foreign bacteria in P. helmanticensis cultures on non-sterile media containing 0.5 g/L SDS was shown to be 2%.