Biochemical Process Engineering, Division of Chemical Engineering, Department of Civil, Environmental, and Natural Resources Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden.
Biochemical Process Engineering, Division of Chemical Engineering, Department of Civil, Environmental, and Natural Resources Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden.
Ultrason Sonochem. 2019 Apr;52:364-374. doi: 10.1016/j.ultsonch.2018.12.010. Epub 2018 Dec 8.
There are only a few reports available about the assimilation of hydrophobic substrates by microorganisms, however, it is well known that oleaginous microorganisms are capable of utilizing both hydrophilic and hydrophobic substrates and accumulate lipids via two different pathways namely de novo and ex novo lipid synthesis, respectively. In the present study, an oleaginous yeast, Cryptococcus curvatus, was investigated for its potentials to utilize a waste substrate of hydrophobic nature (waste cooking oil - WCO) and compared with its ability to utilize a hydrophilic carbon source (glucose). To facilitate the utilization of WCO by C. curvatus, the broth was sonicated to form a stable oil-in-water emulsion without adding any emulsifier, which was then compared with WCO samples without any ultrasound treatment (unsonicated) for the yeast cultivation. Ultrasonication reduces the size of hydrophobic substrates and improves their miscibility in an aqueous broth making them easily assimilated by oleaginous yeast. Under de novo lipid fermentation, the yeast synthesized 9.93 ± 0.84 g/L of cell dry weight and 5.23 ± 0.49 g/L lipids (lipid content of 52.66 ± 0.93% w/w) when cultivated on 40 g/L of glucose (C/N ratio of 40). The amount of cell dry weight, lipid concentration, and lipid content were considerably higher during the ex novo lipid synthesis. More specifically, the highest lipid content achieved was 70.13 ± 1.65% w/w with a corresponding dry cell weight and lipid concentration of 18.62 ± 0.76 g/L and 13.06 ± 0.92 g/L respectively, when grown on 20 g/L sonicated WCO. The highest lipid concentration, however, was observed when the yeast was cultivated on 40 g/L sonicated WCO. Under these conditions, 20.34 g/L lipids were produced with a lipid content of 57.05% w/w. On the other hand, lipid production with unsonicated WCO was significant lower, reaching 11.16 ± 1.02 g/L (69.14 ± 1.34% w/w of lipid content) and 12.21 ± 1.34 g/L (47.39 ± 1.67% w/w of lipid content) for 20 g/L and 40 g/L of WCO, respectively. This underpins the significance of the sonication treatment, especially at elevated WCO concentrations, to improve the accessibility of the yeast to the WCO. Sonication treatment that was used in this study assisted the utilization of WCO without the need to add emulsifiers, thus reducing the need for chemicals and in turn has a positive impact on the production costs. The microbial lipids produced presented a different fatty acid composition compared to the WCO, making them more suitable for biodiesel production as suggested by the theoretical estimation of the biodiesel properties.
目前关于微生物对疏水性基质的同化作用仅有少量报道，但众所周知，产油微生物能够利用亲水性和疏水性基质，并分别通过从头生物合成和新生物合成途径积累脂质。在本研究中，我们研究了一种产油酵母Cryptococcus curvatus 利用疏水性废底物（废食用油-WCO）的潜力，并将其与利用亲水性碳源（葡萄糖）的能力进行了比较。为了促进 C. curvatus 对 WCO 的利用，我们将菌液进行了超声处理，形成了一种稳定的油包水乳状液，而无需添加任何乳化剂，然后将其与未经任何超声处理的 WCO 样品（未超声）进行比较，以用于酵母培养。超声处理可以减小疏水性基质的大小，并提高其在水性培养基中的混溶性，从而使产油酵母更容易同化这些基质。在从头生物合成脂质发酵中，当以 40g/L 葡萄糖（C/N 比为 40）培养时，酵母合成了 9.93±0.84g/L 干细胞重量和 5.23±0.49g/L 脂质（脂质含量为 52.66±0.93%w/w）。在新生物合成脂质时，细胞干重、脂质浓度和脂质含量都显著增加。更具体地说，当在 20g/L 超声处理的 WCO 上生长时，可达到最高的脂质含量 70.13±1.65%w/w，相应的干细胞重量和脂质浓度分别为 18.62±0.76g/L 和 13.06±0.92g/L。然而，当酵母在 40g/L 超声处理的 WCO 上培养时，观察到最高的脂质浓度。在这些条件下，产生了 20.34g/L 的脂质，脂质含量为 57.05%w/w。另一方面，用未超声处理的 WCO 进行脂质生产的效果明显较低，分别达到 11.16±1.02g/L（脂质含量为 69.14±1.34%w/w）和 12.21±1.34g/L（脂质含量为 47.39±1.67%w/w），分别对应于 20g/L 和 40g/L 的 WCO。这突显了超声处理的重要性，尤其是在 WCO 浓度较高的情况下，这可以提高酵母对 WCO 的可利用性。本研究中使用的超声处理有助于在不添加乳化剂的情况下利用 WCO，从而减少对化学品的需求，并反过来对生产成本产生积极影响。与 WCO 相比，所产生的微生物脂质具有不同的脂肪酸组成，这使得它们更适合生物柴油生产，这正如生物柴油性质的理论估算所表明的那样。
