Biosynthesis of polyhydroxyalkanoate (PHA) by <i>Cupriavidus necator</i> KCTC 2649 using coconut ( <i>Cocos nucifera</i> L.) water as carbon source

Polyhydroxyalkanoates (PHA) are biodegradable polymers synthesized by microorganisms under nutrient-deficient conditions. Coconut water, an abundant yet often discarded agro-industrial by-product, is a cost-effective and environmentally friendly substrate rich in carbohydrates such as glucose, fructose, and sucrose. PHAs are typically produced using costly and unsustainable carbon sources. This study investigated the effects of media sterilization methods and carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios on PHA production by <i>Cupriavidus necator</i> KCTC 2649 using coconut water. Among the sterilization methods tested (fresh, autoclaved, filter-sterilized, and synthetic), filter-sterilized media supported the highest PHA yield (4.31 g/L; 0.431 g/g sugar). Optimization of nutrient ratios showed that both C/N and C/P strongly influenced biomass accumulation and polymer yield. Notably, a C/N ratio of 50 combined with a C/P ratio of 10 resulted in maximum biomass growth together with the highest PHA production (5.85 g/L; 59.57% wt/wt; 0.29 g/g sugar). Nutrient limitation at high C/N and C/P ratios promoted PHA accumulation. These findings highlight the potential of coconut water as a sustainable substrate for biomass generation and PHA production by <i>C. necator</i> KCTC 2649.