Research On Lipid Production Of Trichosporon Fermentans On The Industrial And Agricultural Wastes

Single Cell Oils (SCOs, microbial oils) study has become a hot topic during the past decades, because of advantages such as short producing period, little labor required and easy to scale up. However, there are still some restriction factors (i.e. the cost of substrates and high energy consumption) in the application of this biofuel. To improve the economic benefit of SCOs, some industrial and agricultural wastes have been used in the fermentation. Thus, feasible methods of fermentated on wastes for lipid production were investigated in this study. At the same time, the first draft genome and comparative analysis of T. fermentans in our research, laying the foundation for its genetic improvement to facilitate cost-effective lipid production. The results were shown as follows:(1) By co-fermented with sweetpotato vines hydrolysate (SVH), glycerol can be used as an effective substrate for Trichosporon fermentans to produce lipids. Submerged fermentation results showed that T. fermentans exhibited a maximum lipid yield of 7.45 g l-1 with a biomass of 17.95 gl-1 on 10% SVH added glycerol mineral medium (Glycerol MM-10% SVH), which was 4.34-fold higher than that on glycerol mineral medium. Lipids produced on glycerol based media exhibited a significantly different fatty acid composition profile from that produced on sugar based media accompanying by a sharp increase in polyunsaturated fatty acids content. A mathematical model further demonstrated that SVH has a remarkable promoting effect on the biomass formation and glycerol uptake.(2) The co-fermentation of molasses and SVH by Trichosporon fermentans was investigated. T. fermentans showed low lipid accumulation on pure molasses; however, its lipid content was increased 1.35-fold when 10% SVH was added. The strong influence of SVH on lipid production was further demonstrated by the result of sensitivity analysis on effects of factors based on an artificial neural network model because the relative importance value of SVH dosage for lipid production was only lower than that of fermentation time. Scanning electron microscope observation and flow cytometry of yeast cells grown in culture with and without SVH showed that less deformation cells were involved in the culture with SVH. The activity of malic enzyme increased from 2.4 U/mg to 3.7 U/mg after SVH added. All results indicated SVH is a good supplement for lipid fermentation on molasses.(3) This study investigated the differences between the separate hydrolysis and fermentation (SHF) and the simultaneous saccharification and fermentation (SSF) processes in the growth and lipid accumulation of T. fermentans using autoclaved and acid or alkaline hydrolyzed sweetpotato vines (SV). The results showed that SV autoclaving significantly increased the lipid accumulation of T. fermentans compared with acid or alkaline hydrolysis. The effects of different pre-treatments on SV were also studied by scanning electron microscopy and Fourier transform infrared spectroscopy. Moreover, the maximum lipid concentration in SSF was almost 3-fold higher (6.98 g l-1) than that in SHF (2.79 g l-1), and the maximum lipid production increased from 25% in SHF to 36% in SSF. Overall, this study indicated that SSF using autoclaved SV could increase the growth and lipid production of T. fermentans.(4) In this work, T. fermentans CICC 1368, which has been shown to accumulate cellular lipids efficiently using industry-agricultural wastes, was subjected to preliminary genome analysis, yielding a genome size of 31.3 million bases and 12,702 predicted protein-coding genes. Our analysis also showed a high degree of gene duplications and unique genes compared with those observed in other oleaginous yeasts, with 3-4-fold more genes related to fatty acid elongation and degradation compared with those in Rhodosporidium toruloides NP11 and Yarrowia lipolytica CLIB122; Thus, our study provided the first draft genome and comparative analysis of T. fermentans, laying the foundation for its genetic improvement to facilitate cost-effective lipid production.