Production of Polyhydroxyalkanoates (PHA) by Bacillus sp. CYR1 and Cupriavidus sp. CI1 Using Untreated Molasses

Polyhydroxyalkanoate (PHA) is a biodegradable alternative to petroleum-based plastics, but high production costs remain a challenge. Molasses is a promising carbon source and an inexpensive by-product of sugar refining. However, its conventional use requires sucrose hydrolysis pretreatment, which adds cost. Therefore, current study used untreated molasses for PHA polymer production (PHB and PHBV) using Bacillus sp. CYR1 and Cupriavidus sp. CI1. The composition of molasses was confirmed by high-performance liquid chromatography (HPLC) (contains glucose, fructose, and sucrose as major sugars). Precultures of Bacillus sp. CYR1 and Cupriavidus sp. CI1 were inoculated separately (8% v/v) into mineral salts medium containing untreated molasses (conc. = 1, 5, 30, 50, 70, and 100 g/L) and incubated (30°C, 150 rpm) for 24–48 h (n=3). After cultivation, cell biomass was separated using centrifugation (8000 rpm, 10 min) and subjected to alkali treatment after drying. Dry cell weight (DCW) was measured to check bacterial growth, and HPLC was used for PHA production analysis. Cell growth and PHA production increased with molasses concentrations (1 to 70 g/L). Cupriavidus sp. CI1 improved PHB production from 0.017 g/L (DCW = 0.336 g/L) to 2.541 g/L (DCW = 5.873 g/L) at 1 and 70 g/L, but production declined to 0.850 g/L (DCW = 3.958 g/L) at 100 g/L molasses. Likewise, Bacillus sp. CYR1 increased PHBV production from 0.045 g/L (DCW=0.411g/L;13.7 mol% PHB, 86.3 mol% PHV) to 1.789 g/L (DCW = 5.054 g/L; 97.32 mol% PHB, 2.98 mol% PHV) at 70 g/L, however, decrease to 0.298 g/L (DCW = 2.850 g/L) at 100 g/L molasses. The decrease in DCW and PHA production at 100 g/L suggests growth inhibition by high molasses concentration. In conclusion, untreated molasses can be used as a carbon source for PHA production without pretreatment and that, in Bacillus sp. CYR1, molasses concentration influences not only PHA content but also the PHBV monomer composition. Future studies will explore fed-batch cultivation to enhance PHA production efficiency.