Submitted to: Biotechnology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2010
Publication Date: 9/1/2010
Citation: Ashby, R.D., Solaiman, D. 2010. The influence of increasing media methanol concentration on sophorolipid biosynthesis from glycerol-based feedstocks. Biotechnology Letters. 32:1429-1437.
Interpretive Summary: As environmental concerns mount focus has slowly shifted from the use of petroleum-based fuels to more benign alternatives. Biodiesel is one such fuel that is gaining popularity because of its renewable nature and its improved emission characteristics. However, as the biodiesel industry expands more and more crude glycerol (co-product of biodiesel production) is produced, which is necessitating the development of additional outlets for crude glycerol to help maintain its value and offset the production costs of biodiesel itself. One potential application of crude glycerol is as a food (feedstock) for the microbial synthesis of other value-added products. However, crude glycerol from the biodiesel industry typically contains at least low levels of a potentially hazardous alcohol (methanol) that is required for biodiesel synthesis but can be toxic to living organisms. Therefore, in order to utilize the crude glycerol as a feedstock without further preparation (and hence increased cost) it is vital that the microorganisms be able to withstand the deleterious effect of methanol. Sophorolipids (SLs) are biological-detergent molecules that can be synthesized by certain yeasts in large quantities by fermentation. These molecules exhibit properties that permit their use as additives in shampoos, body washes, detergents, cosmetic products and in the lubricant industries and are nontoxic, biodegradable and environmentally benign. In this study we used a glycerol / fat (oleic acid) mixture as feedstock for SL biosynthesis and increased the concentration of methanol in the growth media to 1.5% (v/v; higher than what is typically found in crude glycerol). It was determined that the organism could indeed grow and produce SLs at that methanol concentration but SL yields decreased as the methanol concentration increased. By understanding these effects it will be possible to condition the crude glycerol to maintain a high rate of SL synthesis and provide another outlet for crude glycerol.
Technical Abstract: Candida bombicola, a known producer of sophorolipids (SLs; glycolipid surfactants), was grown on glycerol and oleic acid with up to 1.5% (v/v) of methanol (MeOH; starting concentration) in the fermentation growth media to assess the effects of MeOH presence on SL synthesis and structural distribution. Increasing MeOH concentrations had little effect on the cellular growth of the organism resulting in average cell dry weights (CDW; after SL separation) of 20.8 +/- 0.7 g/L between 0 and 1.5% MeOH. However, increasing MeOH concentrations did decrease SL production by 56% (from 12.7 g/L to 5.6 g/L at 1.5% MeOH) which translated to SL yields on a cellular basis of between 0.60 g SL/g cells (in the absence of MeOH) to 0.27 g SL/g cells (in the presence of 1.5% MeOH). Liquid chromatography/mass spectrometry (LC/MS) revealed that increased MeOH concentrations also resulted in larger concentrations (up to 20 mol%) of free acid SLs but had little effect on the ratios of diacetylated SL lactones synthesized with palmitic acid (4 mol%), linoleic acid (3 mol%), oleic acid (80 mol%), and stearic acid (13 mol%) as the hydrophobic moieties.