Effect of Salt Addition upon the Production of Metabolic Compounds by Yarrowia lipolytica Cultivated on Biodiesel-Derived Glycerol Diluted with Olive-Mill Wastewaters

Abstract

One of the major environmental problems is the highly toxic agro-industrial waste called olive mill wastewater (OMW), deriving from olive oil production. On the other hand, the continuous development of the biological liquid fuel industry (biodiesel and bioethanol) makes it mandatory the process and exploitation of their main by-products, crude glycerol. This study dealt with the biotechnological conversions of biodiesel-derived crude glycerol with the use of the non-conventional yeast Yarrowia lipolytica in media that had been diluted with OMWs. OMWs, employed as simultaneous liquid medium and substrate, is a new trend recently appearing in Industrial Biotechnology, where value-added metabolites could be produced with simultaneous partial detoxification (i.e. decolorization and phenol removal) of the used residue. In the present study, diluted OMWs (containing 2.0 g/L of total phenolic compounds) blended with 70.0 g/L crude glycerol were employed as substrates. Production of value-added compounds by Y. lipolytica strain ACA-YC 5031 was studied in nitrogen-limited media favoring the production of secondary metabolites (i.e. citric acid, polyols, microbial lipids, polysaccharides). Batch-flask cultures were carried out and the impact of the addition of different NaCl concentrations (1.0%, 3.0%, 5.0% w/w) added upon the biochemical behavior of the strain was studied. Remarkable biomass production was observed in all trials, while in the “blank” experiment (no OMWs and no salt added), the metabolism was shifted toward the synthesis of polyols (Σpolyols = mannitol + arabitol + erythritol > 20 g/L and maximum total citric acid-Cit (sum of citric and isocitric acid) = 10.5 g/L). Addition of OMWs resulted in Citmax = 32.7 g/L, while Σpolyols concentration dropped to <15 g/L. Addition of salt in the OMW-based media slightly reduced the produced biomass, while Cit production drastically increased, reaching a final value of 54.0 g/L (conversion yield of Cit produced per unit of glycerol consumed = 0.82 g/g) in the trial with addition of 5.0% NaCl. Finally, significant color and phenols removal were observed, evaluating the yeast as a decontamination medium for the OMW and a great candidate for the production of value-added compounds.

Lipid Production by Yeasts Growing on Commercial Xylose in Submerged Cultures with Process Water Being Partially Replaced by Olive Mill Wastewaters

“…In contrast-and despite the non-negligible dephenolization that occurred-L. starkeyi did not remove at all color from the wastewater. It may be assumed, therefore, that color and phenol removal from phenol-containing wastewaters, seem processes that are not obligatorily implicated to each other, in agreement with results recorded for the detoxification of wastewaters performed by edible and medicinal mushrooms [37,69], several types of yeasts like strains of Y. lipolytica and S. cerevisiae [11,16,18,70] or even crude enzymes deriving from mushroom cultivations [92]. Yeast strains compared to higher fungi, do not possess the mechanisms of producing the appropriate extracellular oxidases [10,13,92] to break down phenolic compounds that are found in several phenol-containing wastewaters [37,38,69,92].…”

“…On the other hand, it must be pointed out that within the range of PCC 0 found in the current investigation (viz. 0.0 up to 2.0 or even 3.0 g/L), similar results concerning the "resistance" of TDCW production-or even the "boost" of growth in the presence of OMWs for other yeast strains-has been reported [11,12,[16][17][18]70]. Specifically, the increment of TDCW production by the strain Saccharomyces cerevisiae MAK-1 in which OMWs were added in various initial concentrations (additions up to PCC 0 ≈ 3.0 g/L) was impressive as compared with the blank experiment (PCC 0 = 0.0 g/L-no OMWs added) [18].…”

“…Contradictory to these results, the addition of OMWs negatively affected the production of SCO in the strain L. starkeyi NRRL Y-11557, than the control experiment (trial on glucose in which no OMWs were added) [68]. Generally, the addition of OMWs can significantly change the spectrum of the final products synthesized by various types of yeasts, compared with the control trials (no OMWs added) [11,12,15,17,70,73]. The kinetics of TDCW and lipid production and total extracellular sugars (mostly xylose) and FAN evolution during growth of C. curvatus in media in which PCC 0 was adjusted to ≈ 1.2 g/L is depicted in Figure 2a,b.…”

“…Specifically, the increment of TDCW production by the strain Saccharomyces cerevisiae MAK-1 in which OMWs were added in various initial concentrations (additions up to PCC 0 ≈ 3.0 g/L) was impressive as compared with the blank experiment (PCC 0 = 0.0 g/L-no OMWs added) [18]. Likewise, various strains of the nonconventional yeast Y. lipolytica noticeably resisted despite the presence of phenolic compounds in significant concentrations (i.e., PCC 0 up to 5.5 g/L) in the media [11,12,17,70,71]. In accordance with the achieved in the present study results, other yeasts belonging to the species Candida cylindracea, C. tropicalis, C. albidus and Trichosporon cutaneum seemed to demonstrate remarkable resistance upon the phenolic compounds of OMWs [15,68,[72][73][74].…”

Sugar Alcohols and Organic Acids Synthesis in Yarrowia lipolytica: Where Are We?

“…Using a mixture of OMW and crude glycerol, the strain ACA-DC 5029 produced CA with a resultant titer of 79 g/L and yield from glycerol of 0.46 g/g in 528 h [32]. For the Y. lipolytica strain ACA-YC 5031, addition of NaCl (%) in OMW-based media significantly increases CA production with titer and yield from glycerol of 54 g/L and 0.82 g/g, respectively [33]. Using 100 g/L sunflower oil as a carbon source, CA titer of 66.2 and 50 g/L were obtained for the Y. lipolytica strain TEM YL 3 and TEM YL 20, respectively [34].…”