Optimization of lipid production from physarum polycephalum in submerged culture

Abstract

Physarum polycephalum is a member of the myxomycetes (plasmodial slime molds or myxogastrids). One of the trophic stages in the life cycle of this organism is a structure known as a plasmodium. In submerged culture, plasmodia are fragmented into microplasmodia. Like a plasmodium, microplasmodia of are free of cell walls, making the extraction of desired compounds from their biomass easy to achieve. In addition, they are reported to be capable of fast growth. However, there has been only limited information on the effects of medium composition on their growth and the rate of lipid accumulation by these organisms. Thus, the present study demonstrated an effective procedure for obtaining a microplasmodial culture from a sclerotium (a resting form of a plasmodium) of P. polycephalum and investigated the effects of medium composition and incubation time on biomass and lipid production. Optimization of medium components by response surface methodology showed that tryptone and yeast extract concentrations had the most significant effects on lipid and biomass production and significant synergistic interactions between glucose and tryptone concentration on these responses also were recorded. The optimal medium was found to be composed of 20 g/L of glucose, 6.59 g/L of tryptone, and 3.0 g/L of yeast extract. This medium yielded 12.2 g/L of biomass and 1.7 g/L of lipids after four days. Examination of the effects of incubation time showed that biomass and lipid production increased over time and reached maximal values between four and five days, then drastically decreased. Fatty acid compositions analysis by GC-MS revealed that P. polycephalum lipid consisted mainly of oleic acid (40.5%), linoleic acid (10%), and octadecynoic (15.8%). This is the first report on the fatty acids composition of P. polycephalum microplasmodia. Based on this information, the biomass of microplasmodia could be used as a source of material for direct conversion into biodiesel because of the lack of cell walls or it also could be used as a supplemental source of beneficial fatty acids for humans, albeit with some further evaluation needed. Keywords: fatty acid compositions, lipids, biodiesel, microplasmodia, Physarum polycephalum, slime molds.