Investigation of the regulation mechanisms for bioplastics production from industrial residues

Abstract

The current high demand for plastics has become unsustainable. Polyhydroxyalkanoates are biopolymers stored by bacteria that can potentially replace modern plastics due to: wide range of applications; biodegradability; use of renewable resources as feedstock. High costs of current Polyhydroxyalkanoates production can be reduced using mixed cultures of organisms. Activated sludge from wastewater treatment plants is selected for Polyhydroxyalkanoates production through the imposition of cycles of intermittent feeding. In this study, the acclimation of activated sludge using synthetic volatile fatty acids (VFAs) as substrate resulted in a culture rich in Paracoccus spp. and unidentified filamentous bacteria. Low cost substrates such as sugarcane molasses (SM) or cheese whey (CW) can be employed as feedstock for further cost reduction. This requires an additional step before the microbial selection to ferment the feedstock into VFAs. In this work, the feedstock was changed from SM to CW. The population fed with SM was rich in Actinomycetaceae, while the population fed with CW was rich in Streptococcaceae, affecting the VFA composition. Consequently, the PHA-storing population and the polymer were affected. In the fermented SM (fSM) phase, the population was rich in Azoarcus (41.5 - 64.6%) and in the fCW phase the population was more diverse. Changing the pH in the fermentation reactor also affected the selection stage with an increase in Thauera and Azoarcus and a decrease in Paracoccus. A significant unidentified population of one layer sheet- forming bacteria was observed. Lastly, the occurrence of cell-to-cell communication (QS) in the selection stage was investigated. Possibly, QS molecules were detected when the carbon source was depleted. All steps of polyhydroxyalkanoate production are interconnected and for optimization, all stages must be studied and improved. Moreover, if QS proves to be involved in polyhydroxyalkanoate storage, the addition of QS molecules to the process may be explored for further optimization.