Microbial production of polyhydroxyalkanoates by bacteria isolated from oil wastes

A Gram-positive coccus-shaped bacterium capable of synthesizing higher rela tive molecular weight (M-r) polyhydroxybutyrate (PHB) was isolated from ses ame oil and identified as Staphylococcus epidermidis (by Microbial ID, Inc. , Newark, NT). The experiment was conducted by shake flask fermentation cul ture using media containing fructose. Cell growth up to a dry mass of 2.5 g /L and PHB accumulation up to 15.02% of cell dry wt was observed. Apart fro m using single carbohydrate as a sole carbon source, various industrial foo d wastes including sesame oil, ice cream, malt, and soya wastes were invest igated as nutrients for S. epidermidis to reduce the cost of the carbon sou rce. As a result, we found that by using malt wastes as nutrient for cell g rowth, PWB accumulation of S. epidermidis was much better than using other wastes as nutrient source. The final dried cell mass and PHB production usi ng malt wastes were 1.76 g/L and 6.93% polymer/cells (grams/gram), and 3.5 g/L and 3.31% polymer/cells (grams/gram) in shake flask culture and in ferm entor culture, respectively. The bacterial polymer was characterized by(1)H -nuclear magnetic resonance (NMR),C-13-NMR, Fourier transform infrared, and differential scanning calorimetry. The results show that with different: i ndustrial food wastes as carbon and energy sources, the same biopolymer (PH B) was obtained. However, the use of sesame oil as the carbon source result ed in the accumulation of PHB with a higher melting point than that produce d from other food wastes as carbon sources by this organism under similar e xperimental conditions.