The Impact of Plastic Additives on the Efficiency of Polyhydroxybutyrate Biodegradation by a Single Bacterial Isolate

Biodegradable plastics have emerged as a promising solution to plastic waste pollution, with increasing efforts directed toward improving their degradation under natural environmental conditions. Among polyhydroxyalkanoates (PHAs), polyhydroxybutyrate (PHB) is the most extensively studied due to its high biodegradability. However, commercial PHB-based materials typically contain various additives to enhance their mechanical properties and processability. Some of these additives are potentially toxic and may leach into the environment, raising concerns about their impact on the microbial degradation of PHB.

This study investigated the influence of selected plastic additives on the biodegradation of PHB. Three additives—benzenesulfonamide (50, 100, and 200 μg/L), dipropylene glycol (50, 100, and 200 μg/L), and triethylene glycol (100, 200, and 500 μg/L)—were evaluated at concentrations equivalent to those commonly found in commercial PHB products. PHB was incorporated into a mineral salt (MS) medium and inoculated with Ralstonia sp. C1, a known PHB-degrading bacterium, under aerobic conditions. Biodegradation was monitored over a 96-hour period by measuring the degradation progress at 24-hour intervals, and the results were compared to those in a control group without additives.

All three additives were degraded by more than 98%, and no significant differences in PHB degradation rates were observed between the additive-treated and control groups. These results suggest that the tested additives do not adversely affect PHB biodegradation. The findings also imply that Ralstonia sp. C1 may tolerate or co-metabolize these compounds, thereby preserving the biodegradability of PHB-based materials in the presence of such additives.