Diamantopoulou Panagiota, Sarris Dimitris, Tchakouteu Sidoine Sadjeu, Xenopoulos Evangelos, Papanikolaou Seraphim
Institute of Technology of Agricultural Products (ITAP), Hellenic Agricultural Organization-Demeter, 1 Sofokli Venizelou Street, Attiki, 14123 Lykovryssi, Greece.
Department of Food Science and Nutrition, School of Environment, University of the Aegean, Metropolite Ioakeim 2, 81400 Myrina, Greece.
Microorganisms. 2023 Jul 24;11(7):1863. doi: 10.3390/microorganisms11071863.
Sugar-rich waste streams, generated in very high quantities worldwide, constitute an important source of environmental pollution. Their eco-friendly conversions into a plethora of added-value compounds through the use of microbial fermentations is currently a very "hot" scientific topic. The aim of this study, was to assess the potential of single cell oil (SCO), microbial mass and citric acid (CA) production by non-conventional yeast strains growing on expired ("waste") glucose. Six yeast strains (. DSM 4444, NRRL YB-252, NRRL Y-27012, LFMB Y-20, ACA-DC 50109 and DSM 70296) were initially grown in shake flasks with expired glucose used as substrate under nitrogen limitation, in order to "boost" the cellular metabolism towards the synthesis of SCO and CA, and their growth response was quantitatively evaluated. Initial glucose concentration (Glc) was adjusted at . 50 g/L. Besides , all other yeast strains produced noticeable SCO quantities [lipid in dry cell weight (DCW) ranging from 25.3% / to 55.1% /]. Lipids of all yeasts contained significant quantities of oleic acid, being perfect candidates for the synthesis of 2nd generation biodiesel. The highest DCW production (=13.6 g/L) was obtained by DSM 70296, while both strains did not accumulate noticeable lipid quantities, but produced non-negligible CA amounts. The most promising CA-producing strain, namely ACA-DC 50109 was further studied in stirred-tank bioreactor systems, while the very promising DCW- and SCO-producing DSM 70296 was further studied in shake flasks. Both strains were grown on media presenting higher Glc concentrations and the same initial nitrogen quantity as previously. Indeed, grown at Glc = 85 g/L, produced DCW = 34.0 g/L, that contained lipid =34.1% / (thus SCO was =11.6 g/L). The strain ACA-DC 50109 in stirred tank bioreactor with Glc ≈ 105 g/L produced CA up to 46 g/L (yield of CA produced on glucose consumed; Y ≈ 0.45 g/g). Finally, in fed-batch bioreactor experiment, the significant CA quantity of 82.0 g/L (Y = 0.50 g/g) was recorded. Concluding, "waste" glucose proved to be a suitable substrate for a number of non-conventional yeast strains. ACA-DC 50109 produced significant quantities of CA while DSM 70296 was a very interesting DCW- and SCO-producing candidate. These strains can be used as potential cell factories amenable to convert glucose-based residues into the mentioned metabolic compounds, that present high importance for food, chemical and biofuel facilities.
富含糖分的废物流在全球产生的数量非常巨大，是环境污染的一个重要来源。通过微生物发酵将其生态友好地转化为大量增值化合物，目前是一个非常“热门”的科学话题。本研究的目的是评估在过期（“废弃”）葡萄糖上生长的非常规酵母菌株生产单细胞油（SCO）、微生物菌体和柠檬酸（CA）的潜力。六种酵母菌株（DSM 4444、NRRL YB - 252、NRRL Y - 27012、LFMB Y - 20、ACA - DC 50109和DSM 70296）最初在摇瓶中，以过期葡萄糖为底物，在氮限制条件下培养，以“促进”细胞代谢向SCO和CA的合成方向发展，并对它们的生长反应进行了定量评估。初始葡萄糖浓度（Glc）调整为50 g/L。此外，所有其他酵母菌株都产生了可观数量的SCO [干细胞重量（DCW）中的脂质含量在25.3%至55.1%之间]。所有酵母的脂质都含有大量的油酸，是合成第二代生物柴油的理想候选物。DSM 70296获得了最高的DCW产量（=13.6 g/L），而这两种菌株都没有积累可观的脂质数量，但产生了不可忽略的CA量。最有前景的产CA菌株，即ACA - DC 50109，在搅拌罐生物反应器系统中进行了进一步研究，而非常有前景的产DCW和SCO的DSM 70296在摇瓶中进行了进一步研究。两种菌株都在葡萄糖浓度更高且初始氮量与之前相同的培养基上生长。实际上，DSM 70296在Glc = 85 g/L时生长，产生了DCW = 34.0 g/L，其中脂质含量为34.1%（因此SCO为11.6 g/L）。ACA - DC 50109在搅拌罐生物反应器中，当Glc≈105 g/L时，产生的CA高达46 g/L（基于消耗的葡萄糖产生CA的产量；Y≈0.45 g/g）。最后，在补料分批生物反应器实验中，记录到了显著的82.0 g/L的CA量（Y = 0.50 g/g）。总之，“废弃”葡萄糖被证明是许多非常规酵母菌株的合适底物。ACA - DC 50109产生了大量的CA，而DSM 70296是一个非常有吸引力的产DCW和SCO的候选菌株。这些菌株可作为潜在的细胞工厂，能够将基于葡萄糖的残渣转化为上述代谢化合物，这些化合物对食品、化工和生物燃料设施具有高度重要性。
