Extracellular fungal polyol lipids: A new class of potential high value lipids.

Extracellular fungal glycolipid biosurfactants have attracted attention because productivities can be high, cheap substrates can be used, the molecules are secreted into the medium and the downstream processing is relatively simple. Three classes of extracellular fungal glycolipid biosurfactants have provided most of the scientific advances in this area, namely sophorolipids, mannosylerythritol lipids and cellobioselipids. Polyol lipids, a fourth class of extracellular fungal glycolipid biosurfactants, comprise two groups of molecules: liamocins produced by the yeast-like fungus Aureobasidium pullulans, and polyol esters of fatty acids, produced by some Rhodotorula yeast species. Both are amphiphilic, surface active molecules with potential for commercial development as surfactants for industrial and household applications. The current knowledge of polyol lipids highlights an emerging group of extracellular fungal glycolipid biosurfactants and provides a perspective of what next steps are needed to harness the benefits and applications of this novel group of molecules.

1-Ethyl-3-methylimidazolium tolerance and intracellular lipid accumulation of 38 oleaginous yeast species.

Pretreatment with ionic liquids (IL) such as 1-ethyl-3-methylimidazolium chloride or acetate is an effective method for aiding deconstruction of lignocellulosic biomass; however, the residual IL remaining in hydrolysates can be inhibitory to growth of ethanologenic or oleaginous yeasts that have been examined in the literature. The aim of this study was to identify oleaginous yeasts that are tolerant of the IL [C2C1Im][OAc] and [C2C1Im]Cl using 45 strains belonging to 38 taxonomically diverse species within phyla Ascomycota and Basidiomycota. Yeasts were cultivated in laboratory medium supplemented with 0, 2, or 4% IL in 96-well plates. The eight most tolerant strains were then cultivated in 10-mL media with no IL, 242mM [C2C1Im][OAc], or 242mM [C2C1Im]Cl. The effects of [C2C1Im]+ exposure on cell mass production and lipid accumulation varied at the species and strain level. The acetate salt decreased cell biomass and lipid production more severely than did the chloride ion for six strains. Lipid output was not markedly different (2.1 vs. 2.3 g/L) in Yarrowia lipolytica UCDFST 51-30, but decreased from 5 to 65% in other yeasts. An equimolar concentration of the chloride salt resulted in much milder effects, from 25% decrease to 66% increase in lipid output. The highest lipid outputs in this media were 8.3 and 7.9 g/L produced by Vanrija humicola UCDFST 10-1004 and UCDFST 12-717, respectively. These results demonstrated substantial lipid production in the presence of [C2C1Im]Cl at concentrations found in lignocellulosic hydrolysates, and thus, these two strains are ideal candidates for further investigation.

Simultaneous production of intracellular triacylglycerols and extracellular polyol esters of fatty acids by Rhodotorula babjevae and Rhodotorula aff. paludigena.

Microbial oils have been analyzed as alternatives to petroleum. However, just a handful of microbes have been successfully adapted to produce chemicals that can compete with their petroleum counterparts. One of the reasons behind the low success rate is the overall economic inefficiency of valorizing a single product. This study presents a lab-scale analysis of two yeast species that simultaneously produce multiple high-value bioproducts: intracellular triacylglycerols (TG) and extracellular polyol esters of fatty acids (PEFA), two lipid classes with immediate applications in the biofuels and surfactant industries. At harvest, the yeast strain Rhodotorula aff. paludigena UCDFST 81-84 secreted 20.9 ± 0.2 g L-1 PEFA and produced 8.8 ± 1.0 g L-1 TG, while the yeast strain Rhodotorula babjevae UCDFST 04-877 secreted 11.2 ± 1.6 g L-1 PEFA and 18.5 ± 1.7 g L-1 TG. The overall glucose conversion was 0.24 and 0.22 g(total lipid) g (glucose)-1 , respectively. The results present a stable and scalable microbial growth platform yielding multiple co-products.

Discovery of synthesis and secretion of polyol esters of fatty acids by four basidiomycetous yeast species in the order Sporidiobolales.

Polyol esters of fatty acids (PEFA) are amphiphilic glycolipids produced by yeast that could play a role as natural, environmentally friendly biosurfactants. We recently reported discovery of a new PEFA-secreting yeast species, Rhodotorula babjevae, a basidiomycetous yeast to display this behavior, in addition to a few other Rhodotorula yeasts reported on the 1960s. Additional yeast species within the taxonomic order Sporidiobolales were screened for secreted glycolipid production. PEFA production equal or above 1 g L-1 were detected in 19 out of 65 strains of yeast screened, belonging to 6 out of 30 yeast species tested. Four of these species were not previously known to secrete glycolipids. These results significantly increase the number of yeast species known to secrete PEFA, holding promise for expanding knowledge of PEFA synthesis and secretion mechanisms, as well as setting the groundwork towards commercialization.

Multiplatform Mass Spectrometry-Based Approach Identifies Extracellular Glycolipids of the Yeast Rhodotorula babjevae UCDFST 04-877.

A multiplatform mass spectrometry-based approach was used for elucidating extracellular lipids with biosurfactant properties produced by the oleaginous yeast Rhodotorula babjevae UCDFST 04-877. This strain secreted 8.6 ± 0.1 g/L extracellular lipids when grown in a benchtop bioreactor fed with 100 g/L glucose in medium without addition of hydrophobic substrate, such as oleic acid. Untargeted reversed-phase liquid chromatography-quadrupole/time-of-flight mass spectrometry (QTOFMS) detected native glycolipid molecules with masses of 574-716 Da. After hydrolysis into the fatty acid and sugar components and hydrophilic interaction chromatography-QTOFMS analysis, the extracellular lipids were found to consist of hydroxy fatty acids and sugar alcohols. Derivatization and chiral separation gas chromatography-mass spectrometry (GC-MS) identified these components as d-arabitol, d-mannitol, (R)-3-hydroxymyristate, (R)-3-hydroxypalmitate, and (R)-3-hydroxystearate. In order to assemble these substructures back into intact glycolipids that were detected in the initial screen, potential structures were in-silico acetylated to match the observed molar masses and subsequently characterized by matching predicted and observed MS/MS fragmentation using the Mass Frontier software program. Eleven species of acetylated sugar alcohol esters of hydroxy fatty acids were characterized for this yeast strain.

Eighteen new oleaginous yeast species.

Of 1600 known species of yeasts, about 70 are known to be oleaginous, defined as being able to accumulate over 20 % intracellular lipids. These yeasts have value for fundamental and applied research. A survey of yeasts from the Phaff Yeast Culture Collection, University of California Davis was performed to identify additional oleaginous species within the Basidiomycota phylum. Fifty-nine strains belonging to 34 species were grown in lipid inducing media, and total cell mass, lipid yield and triacylglycerol profiles were determined. Thirty-two species accumulated at least 20 % lipid and 25 species accumulated over 40 % lipid by dry weight. Eighteen of these species were not previously reported to be oleaginous. Triacylglycerol profiles were suitable for biodiesel production. These results greatly expand the number of known oleaginous yeast species, and reveal the wealth of natural diversity of triacylglycerol profiles within wild-type oleaginous Basidiomycetes.

Oleaginous yeasts for biodiesel: current and future trends in biology and production.

Production of biodiesel from edible plant oils is quickly expanding worldwide to fill a need for renewable, environmentally-friendly liquid transportation fuels. Due to concerns over use of edible commodities for fuels, production of biodiesel from non-edible oils including microbial oils is being developed. Microalgae biodiesel is approaching commercial viability, but has some inherent limitations such as requirements for sunlight. While yeast oils have been studied for decades, recent years have seen significant developments including discovery of new oleaginous yeast species and strains, greater understanding of the metabolic pathways that determine oleaginicity, optimization of cultivation processes for conversion of various types of waste plant biomass to oil using oleaginous yeasts, and development of strains with enhanced oil production. This review examines aspects of oleaginous yeasts not covered in depth in other recent reviews. Topics include the history of oleaginous yeast research, especially advances in the early 20th century; the phylogenetic diversity of oleaginous species, beyond the few species commonly studied; and physiological characteristics that should be considered when choosing yeast species and strains to be utilized for conversion of a given type of plant biomass to oleochemicals. Standardized terms are proposed for units that describe yeast cell mass and lipid production.

Accumulation of high-value lipids in single-cell microorganisms: a mechanistic approach and future perspectives.

In recent years attention has been focused on the utilization of microorganisms as alternatives for industrial and nutritional applications. Considerable research has been devoted to techniques for growth, extraction, and purification of high-value lipids for their use as biofuels and biosurfactants as well as high-value metabolites for nutrition and health. These successes argue that the elucidation of the mechanisms underlying the microbial biosynthesis of such molecules, which are far from being completely understood, now will yield spectacular opportunities for industrial scale biomolecular production. There are important additional questions to be solved to optimize the processing strategies to take advantage of the assets of microbial lipids. The present review describes the current state of knowledge regarding lipid biosynthesis, accumulation, and transport mechanisms present in single-cell organisms, specifically yeasts, microalgae, bacteria, and archaea. Similarities and differences in biochemical pathways and strategies of different microorganisms provide a diverse toolset to the expansion of biotechnologies for lipid production. This paper is intended to inspire a generation of lipid scientists to insights that will drive the biotechnologies of microbial production as uniquely enabling players of lipid biotherapeutics, biofuels, biomaterials, and other opportunity areas into the 21st century.

Peptidomic profile of milk of Holstein cows at peak lactation.

Bovine milk is known to contain naturally occurring peptides, but relatively few of their sequences have been determined. Human milk contains hundreds of endogenous peptides, and the ensemble has been documented for antimicrobial actions. Naturally occurring peptides from bovine milk were sequenced and compared with human milk peptides. Bovine milk samples from six cows in second-stage peak lactation at 78-121 days postpartum revealed 159 peptides. Most peptides (73%) were found in all six cows sampled, demonstrating the similarity of the intramammary peptide degradation across these cows. One peptide sequence, ALPIIQKLEPQIA from bovine perilipin 2, was identical to another found in human milk. Most peptides derived from ß-casein, αs1-casein, and αs2-casein. No peptides derived from abundant bovine milk proteins such as lactoferrin, ß-lactoglobulin, and secretory immunoglobulin A. The enzymatic cleavage analysis revealed that milk proteins were degraded by plasmin, cathepsins B and D, and elastase in all samples.