Development of Dual Phase Hybrid Cultivation System to Enhance Polyhydroxybutyrate (PHB) Production by Synechococcus sp.

The extensive use of petroleum-based plastics has led to severe environmental pollution, emphasizing the need for sustainable alternatives such as biodegradable polyhydroxybutyrate (PHB). Conventional PHB production using heterotrophic microorganisms requires external organic carbon sources, contributing to high production costs. Additionally, the separation of the biomass growth phase and the PHB accumulation phase in conventional systems limits production efficiency. This study introduces a dual-phase hybrid cultivation system designed to achieve simultaneous biomass growth and PHB accumulation in the cyanobacerium Synechococcus sp. The system alternates between a light phase that supports biomass growth via photosynthesis and a dark phase that promotes PHB synthesis. Synechococcus sp. was selected for its ability to fix CO2 as a carbon source, reducing the need for external organic carbon supplementation. To further enhance PHB accumulation, carbon by products extracted from cyanobacteria cell debris—including fatty acids, polysaccharides, and amino acids—were supplemented during cultivation. During the 14-day cultivation period, the hybrid system maintained biomass growth at a level similar to the conventional system. Meanwhile, PHB accumulation reached 7% (w/w DCW), over three times higher than the 2% in the conventional system. This demonstrates the system’s ability to enhance PHB synthesis without compromising biomass growth. carbon by products increased PHB production by approximately 40% compared to the conventional system without supplementation. This represents increases of 13% in PHB yield under non-supplemented conditions. These results indicate that the dual-phase hybrid cultivation system using internal carbon sources improves PHB production and offers a promising approach for bioplastics manufacturing.