Oleaginous yeast-a potential source of renewable oil by ProQuest

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									          inform November 2008, Vol. 19 (11)          763
                                                                                                      Annual Meeting


       Oleaginous yeast—a potential
       source of renewable oil
   This article is based on a presentation given
   by Sam Beattie at the Hot Topic Symposium,
   “Honoring 50 Years of Lipid Research by
   Earl Hammond: Modifying Lipids to Improve
   Food and Fuel,” 99th AOCS Annual Meeting
   & Expo, Seattle, Washington, USA, May 20,
   2008.


       Sam Beattie and Earl Hammond
       Oleaginous fungi are yeasts and molds
       that are able to accumulate over 20%
       of their biomass as lipid, usually tria-
       cylglycerols (single cell oil, SCO). Since
       their discovery in the late 1800s, a
       dozen or so molds and yeasts (Table 1
       and Fig. 1) with the ability to grow fat
       when grown on simple carbon sources
       have been described. possibly the first
       yeast observed to contain oil was the
       common fermentative yeast Saccha-
       romyces cereviseae, which produces            Earl Hammond (left) and Sam Beattie.
       relatively little oil.
            Proposed and actual uses for SCO
       include as alternatives to vegetable oils     source of oils. They made a number of key       lation in some organisms. Once the noncar-
       for human consumption, in production of       observations about growth requirements of       bon nutrient has become limiting, the yeast
       specialty oils or fats, and as alternatives   oleaginous yeast. Lindner and coworkers         shift to synthesizing oil from the carbon
       to petroleum-based fuels. These uses are      showed that oleaginous fermentations re-        source of the medium. An example of the
       somewhat dependent on an inexpensive          quired a medium with a good source of fer-      growth, substrate utilization, and lipid ac-
       and abundant yeast feedstock. Currently,      mentable carbohydrate, a limiting nutrient,     cumulation is shown in Figure 2.
       the major use of oleaginous fungi is in the   and adequate oxygenation. They also expe-            In the 1970s, Nancy Moon and Earl
       production of specialty fatty acids such as   rienced many of the difficulties of achiev-     Hammond isolated the oleaginous yeast
       arachidonic or docosahexaenoic acids by       ing oxygenation in fermentations, which         Candida curvata, since renamed Crypto-
       molds in the Mortierella genus.               remains one of the greatest economic costs      coccus curvatus, from a floor drain in the
            Paul Lindner discovered the oleagi-      of oleaginous fermentations today.              Iowa State University Dairy Plant. This
       nous yeast now known as Metschnikowia              One general feature of lipid accumula-     yeast is able to grow on whey permeate,
       pulcherrima in 1899. and over the years,      tion by oleaginous yeast is that it is a two-   a high-carbon (lactose) low-nitrogen me-
       yeasts with higher oil content have been      phase process. A growth phase in nutrition-     dium, to a fat content of 60% and a cell
       discovered and are listed in Table 1. Lind-   ally complete medium is followed by a de        density of about 15 grams dry yeast/liter
       ner is best known for his work in Germany     novo lipid accumulation phase that begins       of medium. The fatty acid composition re-
       during World War I. Central Europe was        once a key nutrient other than carbon be-       sembles that of palm oil, and about 95%
       cut off from oil imports, and he and co-      comes limiting. Most often, nitrogen is the     of the chemical oxygen demand (COD)
       workers investigated sing
								
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