Abstract
Biodiesel production from vegetable oils is not sustainable and economical due to the food crisis worldwide. The development of a cost-effective non-edible feedstock is essential. In this study, we proposed to use aquatic oomycetes for microbial oils, which are cellulolytic fungus-like filamentous eukaryotic microorganisms, commonly known as water molds. They differ from true fungi as cellulose is present in their cell wall and chitin is absent. They show parasitic as well as saprophytic nature and have great potential to utilize decaying animal and plant debris in freshwater habitats. To study the triacylglycerol (TAG) accumulation in the aquatic oomycetes, the isolated water mold Achlya diffusa was cultivated under semi-solid-state conditions on waste sugarcane bagasse, which was compared with the cultivation in Czapek (DOX) medium. A. diffusa grown on waste sugarcane bagasse showed large lipid droplets in its cellular compartment and synthesized 124.03 ± 1.93 mg/gds cell dry weight with 50.26 ± 1.76% w/w lipid content. The cell dry weight and lipid content of this water mold decreased to 89.54 ± 1.21 mg/gds and 38.82% w/w, respectively, when cultivated on standard medium Czapek-Dox agar (CDA). For the fatty acid profile of A. diffusa grown in sugarcane bagasse and CDA, in situ transesterification (IST) and indirect transesterification (IDT) approaches were evaluated. The lipid profile of this mold revealed the presence of C12:0, C14:0, C16:0, C18:0, C18:1, C18:2, C20:0, and C21:0 fatty acids, which is similar to vegetable oils. The biodiesel properties of the lipids obtained from A. diffusa satisfied the limits as determined by international standards ASTM-D6751 and EN-14214 demonstrating its suitability as a fuel for diesel engines.
Highlights
Biodiesel, as one of the best alternative fuels for transportation and industrial purposes, has various advantages over petrodiesel, such as origination from renewable and indigenous feedstock, low toxicity, better lubricity, superior flash point, and biodegradability (Patel et al 2017b)
The most common oomycetes belong to the family Saprolegniaceae, which includes a wide variety of water molds, showing saprophytic nature as they grow on animals and plant debris or as parasites on plants and animals (Diéguez-Uribeondo et al 2009)
The present study shows for the first time the use of a novel water mold, A. diffusa, for microbial oil production
Summary
As one of the best alternative fuels for transportation and industrial purposes, has various advantages over petrodiesel, such as origination from renewable and indigenous feedstock, low toxicity, better lubricity, superior flash point, and biodegradability (Patel et al 2017b). Lipids produced by microorganisms, involving yeasts, bacteria, fungi, and algae, so-called single cell oil (SCO), are indicated as a promising feedstock for biodiesel production because of their similar fatty acid profile to vegetable oils (Ratledge 2004). These microorganisms can utilize organic carbon sources irrespective of their origin to accumulate oils in their cellular compartment, so-called lipid droplets (LDs), and it has already been reported that the productivity of many microorganisms is higher than that of oil-producing crops (Knothe and Razon 2017). The cell wall of oomycetes has shown similarity with the algal cell wall due to the presence of cellulose (Johnson 1956)
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