The history, state of the art and future prospects for oleaginous yeast research

Abstract

Lipid-based biofuels, such as biodiesel and hydroprocessed esters, are a central part of the global initiative to reduce the environmental impact of the transport sector. The vast majority of production is currently from first-generation feedstocks, such as rapeseed oil, and waste cooking oils. However, the increased exploitation of soybean oil and palm oil has led to vast deforestation, smog emissions and heavily impacted on biodiversity in tropical regions. One promising alternative, potentially capable of meeting future demand sustainably, are oleaginous yeasts. Despite being known about for 143 years, there has been an increasing effort in the last decade to develop a viable industrial system, with currently around 100 research papers published annually. In the academic literature, approximately 160 native yeasts have been reported to produce over 20% of their dry weight in a glyceride-rich oil. The most intensively studied oleaginous yeast have been Cutaneotrichosporon oleaginosus (20% of publications), Rhodotorula toruloides (19%) and Yarrowia lipolytica (19%). Oleaginous yeasts have been primarily grown on single saccharides (60%), hydrolysates (26%) or glycerol (19%), and mainly on the mL scale (66%). Process development and genetic modification (7%) have been applied to alter yeast performance and the lipids, towards the production of biofuels (77%), food/supplements (24%), oleochemicals (19%) or animal feed (3%). Despite over a century of research and the recent application of advanced genetic engineering techniques, the industrial production of an economically viable commodity oil substitute remains elusive. This is mainly due to the estimated high production cost, however, over the course of the twenty-first century where climate change will drastically change global food supply networks and direct governmental action will likely be levied at more destructive crops, yeast lipids offer a flexible platform for localised, sustainable lipid production. Based on data from the large majority of oleaginous yeast academic publications, this review is a guide through the history of oleaginous yeast research, an assessment of the best growth and lipid production achieved to date, the various strategies employed towards industrial production and importantly, a critical discussion about what needs to be built on this huge body of work to make producing a yeast-derived, more sustainable, glyceride oil a commercial reality.

Identification, Quantification and Kinetic Study of Carotenoids and Lipids in Rhodotorula toruloides CBS 14 Cultivated on Wheat Straw Hydrolysate

“…This fatty acid profile is comparable to that of vegetable oils such as palm or sunflower oil [3]. Thus, microbial oil has the potential to be utilized in similar applications as vegetable oil, e.g., the production of biodiesel [4,5], or the production of pharmaceuticals and cosmetics, as well as in the nutritional sector [6,7].…”

Exploring Yeast Diversity to Produce Lipid-Based Biofuels from Agro-Forestry and Industrial Organic Residues

“…In the phylum Ascomycota, yeasts from the genera Lipomyces and Candida , and the species Yarrowia lipolytica were extensively studied due to their intrinsic lipid production potential [ 18 , 21 , 22 , 23 ]. There are sixteen species of the genus Lipomyces, with the Lipomyces starkeyi and Lipomyces tetrasporus species being isolated worldwide [ 24 ].…”

“…Rhodotorula species are present in several habitats such as bark-beetles, tree exudates, plants and vegetables, soil, fresh water, coastal sediments and marine environments but were also isolated from clinical samples [ 31 ]. These yeasts, known as red yeasts, exhibit a red colour due to the production of carotenoids and can exist both in the yeast or in mycelial forms [ 18 ]. Remarkably, the species R. toruloides presents a huge potential as a workhorse for biotechnological applications [ 32 ].…”

“…In addition to the aforementioned advantages, oleaginous yeasts also have the potential to metabolise diverse carbon sources of difficult catabolism, can exhibit high tolerance to a wider range of relevant bioprocess-associated stresses and have an unusual and specialised metabolism producing a wide and diverse repertoire of lipids, proteins and metabolites with high commercialisation potential [ 13 , 14 , 15 , 16 , 17 ]. Although there are over 160 yeast species described as oleaginous, only a small set of these species are relatively well characterised, including Lipomyces starkeyi, Yarrowia lipolytica , Rhodotorula glutinis , Rhodosporidium/Rhodotorula toruloides , Cutaneotrichosporon oleaginosus (previously classified as Cryptococcus curvatus or Trichosporon oleaginosus ) and Cutaneotrichosporon cutaneum (formerly known as Trichosporon cutaneum ) [ 18 ]. These non- Saccharomyces yeast species are referred to as non-conventional yeasts.…”

Metabolic Engineering Strategies for Improved Lipid Production and Cellular Physiological Responses in Yeast Saccharomyces cerevisiae

“…Around 60 species of oleaginous yeasts can produce high yields of TAG, more than 20% dry cell weight (DCW), such as Yarrowia lipolytica , Cutaneotrichosporon oleaginosus, Lipomyces starkeyi, and Rhodosporidium toruloides [ 21 ]. These oleaginous yeasts have naturally evolved with high flux pathways for fatty acids in the form of neutral lipids, which can be converted into a variety of drop-in fuels and oleochemicals [ 22 ].…”