Monteiro de Oliveira Paola, Aborneva Daria, Bonturi Nemailla, Lahtvee Petri-Jaan
Institute of Technology, University of Tartu, Tartu, Estonia.
Front Bioeng Biotechnol. 2021 Apr 29;9:659472. doi: 10.3389/fbioe.2021.659472. eCollection 2021.
Lignocellulosic biomass is an attractive raw material for the sustainable production of chemicals and materials using microbial cell factories. Most of the existing bioprocesses focus on second-generation ethanol production using genetically modified , however, this microorganism is naturally unable to consume xylose. Moreover, extensive metabolic engineering has to be carried out to achieve high production levels of industrially relevant building blocks. Hence, the use of non- species, or non-conventional yeasts, bearing native metabolic routes, allows conversion of a wide range of substrates into different products, and higher tolerance to inhibitors improves the efficiency of biorefineries. In this study, nine non-conventional yeast strains were selected and screened on a diluted hemicellulosic hydrolysate from Birch. CBS 6556, CBS 5773, DSM 70295, and CCT 7815 were selected for further characterization, where their growth and substrate consumption patterns were analyzed under industrially relevant substrate concentrations and controlled environmental conditions in bioreactors. CBS 6556 performed poorly under higher hydrolysate concentrations, although this yeast was determined among the fastest-growing yeasts on diluted hydrolysate. CBS 5773 demonstrated a low growth and biomass production while consuming glucose, while during the xylose-phase, the specific growth and sugar co-consumption rates were among the highest of this study (0.17 h and 0.37 g/gdwh, respectively). DSM 70295 and CCT 7815 were the fastest to consume the provided sugars at high hydrolysate conditions, finishing them within 54 and 30 h, respectively. CCT 7815 performed the best of all four studied strains and tested conditions, showing the highest specific growth (0.23 h), substrate co-consumption (0.73 ± 0.02 g/gdwh), and xylose consumption (0.22 g/gdw*h) rates. Furthermore, CCT 7815 was able to produce 10.95 ± 1.37 gL and 1.72 ± 0.04 mgL of lipids and carotenoids, respectively, under non-optimized cultivation conditions. The study provides novel information on selecting suitable host strains for biorefinery processes, provides detailed information on substrate consumption patterns, and pinpoints to bottlenecks possible to address using metabolic engineering or adaptive evolution experiments.
木质纤维素生物质是利用微生物细胞工厂可持续生产化学品和材料的一种有吸引力的原料。现有的大多数生物工艺都集中在使用转基因微生物生产第二代乙醇，然而，这种微生物天然无法消耗木糖。此外，必须进行广泛的代谢工程才能实现工业相关构件的高产水平。因此，使用具有天然代谢途径的非酿酒酵母属物种或非常规酵母，可以将多种底物转化为不同产品，并且对抑制剂的更高耐受性提高了生物精炼厂的效率。在本研究中，从桦木的稀释半纤维素水解物中选择并筛选了九种非常规酵母菌株。选择了CBS 6556、CBS 5773、DSM 70295和CCT 7815进行进一步表征，在生物反应器中与工业相关的底物浓度和受控环境条件下分析它们的生长和底物消耗模式。CBS 6556在较高水解物浓度下表现不佳，尽管该酵母在稀释水解物上被确定为生长最快的酵母之一。CBS 5773在消耗葡萄糖时生长和生物量产量较低，而在木糖阶段，比生长速率和糖共消耗速率是本研究中最高的（分别为0.17 h⁻¹和0.37 g/gdwh）。DSM 70295和CCT 7815在高水解物条件下消耗所提供糖的速度最快，分别在54小时和30小时内完成。在所有四个研究菌株和测试条件中，CCT 7815表现最佳，显示出最高的比生长速率（0.23 h⁻¹）、底物共消耗速率（0.73±0.02 g/gdwh）和木糖消耗速率（0.22 g/gdw*h）。此外，在非优化培养条件下，CCT 7815能够分别产生10.95±1.37 g/L和1.72±0.04 mg/L的脂质和类胡萝卜素。该研究提供了关于为生物精炼工艺选择合适宿主菌株的新信息，提供了关于底物消耗模式的详细信息，并指出了可能通过代谢工程或适应性进化实验解决的瓶颈问题。
