Oleaginous yeasts from Ethiopia.

Tamene Milkessa Jiru,Dawit Abate,Carolina Pohl,Nicholas Kiggundu,Marizeth Groenewald

doi:10.1186/s13568-016-0242-8

Abstract

Oleaginous microorganisms can produce high amounts of oil (>20 % of their biomass) under suitable cultivation conditions. In this research work 200 samples were collected from soil, plant surfaces (leaves, flowers and fruits), waste oils from traditional oil milling houses and dairy products (cheese, milk and yoghurt) in Ethiopia. Three hundred and forty yeast colonies were isolated from these samples. By applying Sudan III staining tests, 18 strains were selected as possible oleaginous yeasts. The 18 strains were identified and characterized for their lipid production as a feedstock for biodiesel production in the future. They were identified using morphological and physiological methods as well as sequencing the 3′end of the small-subunit rRNA gene, the internal transcribed spacer regions (ITS; ITS 1, ITS 2 and the intervening 5.8S rRNA gene), and the D1/D2 domain of the 26S rRNA gene. The 18 yeasts were identified as Cutaneotrichosporon curvatus (syn, Cryptococcus curvatus) (PY39), Rhodotorula kratochvilovae (syn, Rhodosporidium kratochvilovae) (SY89), Rhodotorula dairenensis (SY94) and Rhodotourula mucilaginosa (SY09, SY18, SY20, PY21, PY23, PY25, SY30, PY32, SY43, PY44, SY52, PY55, PY61, SY75 and PY86). Under nitrogen-limited cultivation conditions, R. mucilaginosa PY44 produced the highest biomass (15.10 ± 0.54 g/L), while R. mucilaginosa PY32 produced the lowest biomass (10.32 ± 0.18 g/L). The highest lipid yield of 6.87 ± 0.62 g/L and lipid content of 46.51 ± 0.70 % were attained by C. curvatus (syn, C. curvatus) PY39. On the other hand, R. mucilaginosa PY61 gave the lowest lipid yield (2.06 ± 0.52 g/L) and R. mucilaginosa SY52 gave the lowest lipid content of 16.99 ± 0.85 %. The results in this research work suggest that much more oleaginous yeasts can be isolated from Ethiopian environment. On the basis of their substantial lipid production abilities, the three oleaginous yeast strains PY39, SY89 and SY18 were selected and recommended for further optimization processes.

Highlights

Oleaginous microorganisms can produce high amounts of oil (>20 % of their biomass) under suitable cultivation conditions (Wynn and Ratledge 2006). These types of organisms can belong to yeasts, filamentous fungi, microalgae and bacteria. They are of great interest due to their ability to accumulate high amounts of lipids in separate lipid bodies (Drucken 2008; Li et al 2008), high lipid production rate, their relatively high growth rates and the resemblance of their TAGs to plant oils (Pan et al 2009; Kosa and Ragauskas 2010).Their production is not influenced by external factors such as their origin, season or climatic changes
For the maximum production of lipid by oleaginous microorganisms, the culture medium has to be provided with an excess of carbon source and limited amount of nitrogen sources (Ratledge 2004)
The best studied oleaginous yeasts belong to the in genera Candida, Cryptococcus, Lipomyces, Rhodosporidium, Rhodotorula, Trichosporon and Yarrowia (Pan et al 2009)

Summary

Introduction

Oleaginous microorganisms can produce high amounts of oil (>20 % of their biomass) under suitable cultivation conditions (Wynn and Ratledge 2006). These types of organisms can belong to yeasts, filamentous fungi, microalgae and bacteria. The best studied oleaginous yeasts belong to the in genera Candida, Cryptococcus, Lipomyces, Rhodosporidium, Rhodotorula, Trichosporon and Yarrowia (Pan et al 2009). The oleaginous yeast strain Cryptococcus curvatus is renamed as Cutaneotrichosporon curvatus (Liu et al 2015). Rhodosporidium has been transferred to Rhodotorula and the oleaginous yeast Rhodosporidium kratochvilovae

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