The Production of Lipids Using 5-Hydorxymethy Furfural Tolerant Rhodotorula graminis Grown on the Hydrolyzates of Steam Pretreated Softwoods

Seiji Nakagame,Jack N Saddler,Yuta Shimizu

doi:10.3390/su12030755

Seiji Nakagame, Jack N Saddler + Show 1 more

Open Access

https://doi.org/10.3390/su12030755

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Abstract

Acid catalyzed (SO2) steam pretreated softwoods inevitably contain furans such as 5-hydorxymethy furfural (HMF) and furfural, which are derived from the respective degradation of component hexoses and pentoses. As these materials are known to be inhibitory to fermentation, six oleaginous yeasts were grown on corn steep liquor (CSL) medium containing HMF (0.2%) and furfural (0.1%) to assess their resistance to possible inhibition and its possible influence on lipid production. R. graminis showed the highest tolerance to HMF (0.2%) and furfural (0.1%) when they were added individually to the CSL medium. However, when both HMF (0.2%) and furfural (0.1%) were added together, this inhibited the growth of R. graminis. Subsequent evaporation of the CSL medium successfully removed furfural from the CSL medium and increased the sugar concentration. However, the residual concentration of HMF (0.4%) still inhibited R. graminis growth. To try to improve HMF tolerance, R. graminis was slowly acclimatized in medium containing HMF (0.4%) and was eventually able to produce 1.8 g/L of lipids after four days of growth in the HMF containing medium. This was close to the same amount of lipid produced as when R. graminis was grown in the CSL medium without HMF and furfural. This indicated that an acclimatization strategy is a promising way to enhance lipids production when R. graminis is grown on the hydrolyzates of SO2-catalyzed steam pretreated lignocellulosic substrates.

Highlights

The production of biodiesel and jet fuel from lignocellulosic materials is one way of reducing the world’s dependence on fossil fuels [1,2]
The growth rates of six oleaginous yeasts, T. oleaginosus, R. graminis, two L. starkeyi, L. spencer-martinsiae, and Y. lipolytica, which were reported as the promising strains for producing lipids from the pretreated lignocellulosic biomass [5], were compared to determine the strain that is adequate for the production of lipids from the hydrolyzates of SO2-catalyzed steam pretreated lignocellulosic biomass
It was known that the presence of inhibitors (HMF, furfural), monomeric sugar concentrations, and sugar compositions affected the production of lipids from the pretreated lignocellulosic biomass [5]

Summary

Introduction

The production of biodiesel and jet fuel from lignocellulosic materials is one way of reducing the world’s dependence on fossil fuels [1,2]. Lignocellulosic materials have the potential to act as the substrates for growing oleaginous yeasts, the recalcitrance of biomass means that typically, some form of pretreatment is required prior to enzymatic hydrolysis of cellulose and hemicellulose [6,7]. After the SO2-catalyzed steam pretreatment, lignocellulosic substrates are recovered as water insoluble fractions, while a part of cellulose and hemicellulose, was depolymerized into oligomeric or monomeric sugars that dissolved in water soluble fractions [6,8]. To produce biodiesel from the hydrolyzates of SO2-catalyzed steam pretreated lignocellulosic biomass using oleaginous yeast, the effect of HMF and furfural on the growth of six oleaginous yeasts were compared. To evaluate the availability of the HMF (0.4%) tolerant R. graminis, the productivity of lipids by the strain in the presence of HMF (0.4%) was examined

Microorganisims

Yeast Screening

Analytical Methods

Results and Discussion