Ionic Liquid Tolerance of Yeasts in Family Dipodascaceae and Genus Wickerhamomyces

In previous studies of ionic liquid (IL) tolerance of numerous species of ascomycetous yeasts, two strains of Wickerhamomyces ciferrii and Galactomyces candidus had unusually high tolerance in media containing up to 5% (w/v) of the 1-ethyl-3-methylimidazolium acetate ([C₂C₁Im][OAc]). The study aimed at investigating whether additional strains of these species, and additional species in the Dipodascaceae family, also possess IL tolerance, and to compare sensitivity to the acetate and chloride versions of the ionic liquid. Fifty five yeast strains in the family Dipodascaceae, which encompasses genera Galactomyces, Geotrichum, and Dipodascus, and seven yeast strains of species Wickerhamomyces ciferrii were tested for ability to grow in laboratory medium containing no IL, 242 mM [C₂C₁Im][OAc], or 242 mM [C₂C₁Im]Cl, and in IL-pretreated switchgrass hydrolysate. Many yeasts exhibited tolerance of one or both ILs, with higher tolerance of the chloride anion than of the acetate anion. Different strains of the same species exhibited varying degrees of IL tolerance. Galactomyces candidus, UCDFSTs 52-260, and 50-64, had exceptionally robust growth in [C₂C₁Im][OAc], and also grew well in the switchgrass hydrolysate. Identification of IL tolerant and IL resistant yeast strains will facilitate studies of the mechanism of IL tolerance, which could include superior efflux, metabolism or exclusion.

Microbial Lipid Alternatives to Plant Lipids

Lipids are in high demand in food production, nutritional supplements, detergents, lubricants, and biofuels. Different oil seeds produced from plants are conventionally extracted to yield lipids. With increasing population and reduced availability of cultivable land, conventional methods of producing lipids alone will not satisfy increasing demand. Lipids produced using different microbial sources are considered as sustainable alternative to plant derived lipids. Various microorganisms belonging to the genera of algae, bacteria, yeast, fungi, or marine-derived microorganisms such as thraustochytrids possess the ability to accumulate lipids in their cells. A variety of microbial production technologies are being used to cultivate these organisms under specific conditions using agricultural residues as carbon source to be cost competitive with plant derived lipids. Microbial oils, also known as single cell oils, have many advantages when compared with plant derived lipids, such as shorter life cycle, less labor required, season and climate independence, no use of arable land and ease of scale-up. In this chapter we compare the lipids derived from plants and different microorganisms. We also highlight various analytical techniques that are being used to characterize the lipids produced in oleaginous organisms and their applications in various processes.

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.

Yeast culture collections in the twenty-first century: new opportunities and challenges

The twenty-first century has brought new opportunities and challenges to yeast culture collections, whether they are long-standing or recently established. Basic functions such as archiving, characterizing and distributing yeasts continue, but with expanded responsibilities and emerging opportunities. In addition to a number of well-known, large public repositories, there are dozens of smaller public collections that differ in the range of species and strains preserved, field of emphasis and services offered. Several collections have converted their catalogues to comprehensive databases and synchronize them continuously through public services, making it easier for users worldwide to locate a suitable source for specific yeast strains and the data associated with these yeasts. In-house research such as yeast taxonomy continues to be important at culture collections. Because yeast culture collections preserve a broad diversity of species and strains within a species, they are able to make discoveries in many other areas as well, such as biotechnology, functional, comparative and evolution genomics, bioprocesses and novel products. Due to the implementation of the Convention of Biological Diversity (CBD) and the Nagoya Protocol (NP), there are new requirements for both depositors and users to ensure that yeasts were collected following proper procedures and to guarantee that the country of origin will be considered if benefits arise from a yeast's utilization. Intellectual property rights (IPRs) are extremely relevant to the current access and benefit-sharing (ABS) mechanisms; most research and development involving genetic resources and associated traditional knowledge will be subject to this topic. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Identification of oleaginous yeast strains able to accumulate high intracellular lipids when cultivated in alkaline pretreated corn stover

Microbial oil is a potential alternative to food/plant-derived biodiesel fuel. Our previous screening studies identified a wide range of oleaginous yeast species, using a defined laboratory medium known to stimulate lipid accumulation. In this study, the ability of these yeasts to grow and accumulate lipids was further investigated in synthetic hydrolysate (SynH) and authentic ammonia fiber expansion (AFEX™)-pretreated corn stover hydrolysate (ACSH). Most yeast strains tested were able to accumulate lipids in SynH, but only a few were able to grow and accumulate lipids in ACSH medium. Cryptococcus humicola UCDFST 10-1004 was able to accumulate as high as 15.5 g/L lipids, out of a total of 36 g/L cellular biomass when grown in ACSH, with a cellular lipid content of 40 % of cell dry weight. This lipid production is among the highest reported values for oleaginous yeasts grown in authentic hydrolysate. Preculturing in SynH media with xylose as sole carbon source enabled yeasts to assimilate both glucose and xylose more efficiently in the subsequent hydrolysate medium. This study demonstrates that ACSH is a suitable medium for certain oleaginous yeasts to convert lignocellullosic sugars to triacylglycerols for production of biodiesel and other valuable oleochemicals.

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.

Manipulation of culture conditions alters lipid content and fatty acid profiles of a wide variety of known and new oleaginous yeast species

Oleaginous yeasts have been studied for oleochemical production for over 80 years. Only a few species have been studied intensely. To expand the diversity of oleaginous yeasts available for lipid research, we surveyed a broad diversity of yeasts with indicators of oleaginicity including known oleaginous clades, and buoyancy. Sixty-nine strains representing 17 genera and 50 species were screened for lipid production. Yeasts belonged to Ascomycota families, Basidiomycota orders, and the yeast-like algal genus Prototheca. Total intracellular lipids and fatty acid composition were determined under different incubation times and nitrogen availability. Thirteen new oleaginous yeast species were discovered, representing multiple ascomycete and basidiomycete clades. Nitrogen starvation generally increased intracellular lipid content. The fatty acid profiles varied with the growth conditions regardless of taxonomic affiliation. The dominant fatty acids were oleic acid, palmitic acid, linoleic acid, and stearic acid. Yeasts and culture conditions that produced fatty acids appropriate for biodiesel were identified.

Drosophila regulate yeast density and increase yeast community similarity in a natural substrate

Drosophila melanogaster adults and larvae, but especially larvae, had profound effects on the densities and community structure of yeasts that developed in banana fruits. Pieces of fruit exposed to adult female flies previously fed fly-conditioned bananas developed higher yeast densities than pieces of the same fruits that were not exposed to flies, supporting previous suggestions that adult Drosophila vector yeasts to new substrates. However, larvae alone had dramatic effects on yeast density and species composition. When yeast densities were compared in pieces of the same fruits assigned to different treatments, fruits that developed low yeast densities in the absence of flies developed significantly higher yeast densities when exposed to larvae. Across all of the fruits, larvae regulated yeast densities within narrow limits, as compared to a much wider range of yeast densities that developed in pieces of the same fruits not exposed to flies. Larvae also affected yeast species composition, dramatically reducing species diversity across fruits, reducing variation in yeast communities from one fruit to the next (beta diversity), and encouraging the consistent development of a yeast community composed of three species of yeast (Candida californica, C. zemplinina, and Pichia kluvyeri), all of which were palatable to larvae. Larvae excreted viable cells of these three yeast species in their fecal pools, and discouraged the growth of filamentous fungi, processes which may have contributed to their effects on the yeast communities in banana fruits. These and other findings suggest that D. melanogaster adults and their larval offspring together engage in 'niche construction', facilitating a predictable microbial environment in the fruit substrates in which the larvae live and develop.

The atzB gene of Pseudomonas sp. strain ADP encodes the second enzyme of a novel atrazine degradation pathway

We previously reported the isolation of a 21.5-kb genomic DNA fragment from Pseudomonas sp. strain ADP, which contains the atzA gene, encoding the first metabolic step for the degradation of the herbicide atrazine (M. de Souza, L. P. Wackett, K. L. Boundy-Mills, R. T. Mandelbaum, and M. J. Sadowsky, Appl. Environ. Microbiol. 61:3373-3378, 1995). In this study, we show that this fragment also contained the second gene of the atrazine metabolic pathway, atzB. AtzB catalyzed the transformation of hydroxyatrazine to N-isopropylammelide. The product was identified by use of high-performance liquid chromatography, mass spectrometery, and nuclear magnetic resonance spectroscopy. Tn5 mutagenesis of pMD1 was used to determine that atzB was located 8 kb downstream of atzA. Hydroxyatrazine degradation activity was localized to a 4.0-kb ClaI fragment, which was subcloned into the vector pACYC184 to produce plasmid pATZB-2. The DNA sequence of this region was determined and found to contain two large overlapping divergent open reading frames, ORF1 and ORF2. ORF1 was identified as the coding region of atzB by demonstrating that (i) only ORF1 was transcribed in Pseudomonas sp. strain ADP, (ii) a Tn5 insertion in ORF2 did not disrupt function, and (iii) codon usage was consistent with ORF1 being translated. AtzB had 25% amino acid identity with TrzA, a protein that catalyzes a hydrolytic deamination of the s-triazine substrate melamine. The atzA and atzB genes catalyze the first two steps of the metabolic pathway in a bacterium that rapidly metabolizes atrazine to carbon dioxide, ammonia, and chloride.

Cloning, characterization, and expression of a gene region from Pseudomonas sp. strain ADP involved in the dechlorination of atrazine

We previously identified a Pseudomonas sp. strain, ADP, which rapidly metabolized atrazine in liquid culture, agar plates, and soils (R. T. Mandelbaum, D. L. Allan, L. P. Wackett, Appl. Environ. Microbiol. 61:1451-1457, 1995). In this study, we report the cloning and partial characterization of a gene region from Pseudomonas sp. strain ADP that encodes atrazine degradation activity. A 22-kb EcoRI genomic DNA fragment, designated pMD1, was shown to encode atrazine dechlorination activity in Escherichia coli DH5 alpha. Atrazine degradation was demonstrated by a zone-clearing assay on agar medium containing crystalline atrazine and by chromatographic methods. A gene conferring the atrazine-clearing phenotype was subsequently subcloned as a 1.9-kb AvaI fragment in pACYC184, designated pMD4, and was expressed in E. coli. This result and random Tn5 mutagenesis established that the 1.9-kb AvaI fragment was essential for atrazine dechlorination. High-pressure liquid and thin-layer chromatographic analyses were used to rigorously establish that E. coli containing pMD4 degraded atrazine and accumulated hydroxyatrazine. Hydroxyatrazine was detected only transiently in E. coli containing pMD1. This is consistent with the idea that hydroxyatrazine is the first metabolite in atrazine degradation by Pseudomonas sp. strain ADP. A 0.6-kb ApaI-PstI fragment from pMD4, containing the putative atrazine chlorohydrolase gene, hybridized to DNA from atrazine-degrading bacteria isolated in Switzerland and Louisiana.(ABSTRACT TRUNCATED AT 250 WORDS)

A Saccharomyces cerevisiae RAD52 allele expressing a C-terminal truncation protein: activities and intragenic complementation of missense mutations

A nonsense allele of the yeast RAD52 gene, rad52-327, which expresses the N-terminal 65% of the protein was compared to two missense alleles, rad52-1 and rad52-2, and to a deletion allele. While the rad52-1 and the deletion mutants have severe defects in DNA repair, recombination and sporulation, the rad52-327 and rad52-2 mutants retain either partial or complete capabilities in repair and recombination. These two mutants behave similarly in most tests of repair and recombination during mitotic growth. One difference between these two alleles is that a homozygous rad52-2 diploid fails to sporulate, whereas the homozygous rad52-327 diploid sporulates weakly. The low level of sporulation by the rad52-327 diploid is accompanied by a low percentage of spore viability. Among these viable spores the frequency of crossing over for markers along chromosome VII is the same as that found in wild-type spores. rad52-327 complements rad52-2 for repair and sporulation. Weaker intragenic complementation occurs between rad52-327 and rad52-1.