Coproduction of polyhydroxyalkanoates and exopolysaccharide by submerged fermentation using autochthonous bacterial strains

For the exploration of production systems of biodegradable polymers, 11 bacteria were isolated from the process of obtaining sugar, of which three showed the ability to produce polyhydroxyalkanoates by the confirmatory methods of staining with Sudan Black and fluorescence appearance in a Petri dish in the presence of Nile blue. The strains with the ability to produce polyhydroxyalkanoates were characterized by their macroscopic and microscopic morphologies and by biochemical tests, and two strains were identified on the genetic basis of 16S rRNA gene sequence Bacillus thuringiensis HA1, and Suhomyces kilbournensis HD1, while isolate AJ1 could not be identified. With the three strains, the production capacity of PHAs and exopolysaccharides by submerged fermentation was explored, and the maximum concentrations of PHAs after 72 h of culture were found to be 0.058, 0.044, and 0.148 g L⁻¹ for the strains Bacillus thuringiensis HA1, isolate AJ1, and Suhomyces kilbournensis HD1, respectively. Likewise, the maximum exopolysaccharide yields were 15, 16.5, and 86 mg L⁻¹ by isolate AJ1, Bacillus thuringiensis HA1, and Suhomyces kilbournensis HD1, respectively. Growth kinetics were also determined using the Gompertz model, and the results showed a direct correlation between the maximum specific growth rate (µ_max) and PHAs production at the higher µ_max and higher PHAs production rate. Finally, Fourier Transform Infrared analysis showed that the polyhydroxyalkanoates produced by the three bacterial strains were Polyhydroxybutyrate, while the exopolysaccharide showed spectra corresponding to inulin for isolate AJ1 and levan for Bacillus thuringiensis HA1 and Suhomyces kilbournensis HD1. Graphical abstract: [Figure not available: see fulltext.]