Polyhydroxyalkanoates (PHAs) synthesis and degradation by microbes and applications towards a circular economy.

Overusing non-degradable plastics causes a series of environmental issues, inferring a switch to biodegradable plastics. Polyhydroxyalkanoates (PHAs) are promising biodegradable plastics that can be produced by many microbes using various substrates from waste feedstock. However, the cost of PHAs production is higher compared to fossil-based plastics, impeding further industrial production and applications. To provide a guideline for reducing costs, the potential cheap waste feedstock for PHAs production have been summarized in this work. Besides, to increase the competitiveness of PHAs in the mainstream plastics economy, the influencing parameters of PHAs production have been discussed. The PHAs degradation has been reviewed related to the type of bacteria, their metabolic pathways/enzymes, and environmental conditions. Finally, the applications of PHAs in different fields have been presented and discussed to induce comprehension on the practical potentials of PHAs.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture.

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting.