Ranieri Raffaella, Candeliere Francesco, Moreno-García Jaime, Mauricio Juan Carlos, Rossi Maddalena, Raimondi Stefano, Amaretti Alberto
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Department of Agricultural Chemistry, Edaphology and Microbiology, University of Cordoba, Cordoba, Spain.
Front Bioeng Biotechnol. 2024 Jan 18;12:1339093. doi: 10.3389/fbioe.2024.1339093. eCollection 2024.
Xylitol is a pentose-polyol widely applied in the food and pharmaceutical industry. It can be produced from lignocellulosic biomass, valorizing second-generation feedstocks. Biotechnological production of xylitol requires scalable solutions suitable for industrial scale processes. Immobilized-cells systems offer numerous advantages. Although fungal pellet carriers have gained attention, their application in xylitol production remains unexplored. In this study, the yeast strain WC 1507 was employed for xylitol production. The optimal conditions were observed with free-cell cultures at pH above 3.5, low oxygenation, and medium containing (NH)SO and yeast extract as nitrogen sources (xylitol titer 79.4 g/L, Y 66.3%, and volumetric productivity 1.3 g/L/h). Yeast cells were immobilized using inactive pellet mycelial carrier (MC) and alginate beads (AB) and were tested in flasks over three consecutive production runs. Additionally, the effect of a 0.2% w/v alginate layer, coating the outer surface of the carriers (cMC and cAB, respectively), was examined. While Y values observed with both immobilized and free cells were similar, the immobilized cells exhibited lower final xylitol titer and volumetric productivity, likely due to mass transfer limitations. AB and cAB outperformed MC and cMC. The uncoated AB carriers were tested in a laboratory-scale airlift bioreactor, which demonstrated a progressive increase in xylitol production in a repeated batch process: in the third run, a xylitol titer of 63.0 g/L, Y of 61.5%, and volumetric productivity of 0.52 g/L/h were achieved. This study confirmed WC 1507 as a promising strain for xylitol production in both free- and entrapped-cells systems. Considering the performance of the wild strain, a metabolic engineering intervention aiming at further improving the efficiency of xylitol production could be justified. MC and AB proved to be viable supports for cell immobilization, but additional process development is necessary to identify the optimal bioreactor configuration and fermentation conditions.
木糖醇是一种广泛应用于食品和制药行业的戊糖醇。它可以由木质纤维素生物质生产,从而使第二代原料具有价值。木糖醇的生物技术生产需要适合工业规模工艺的可扩展解决方案。固定化细胞系统具有许多优点。尽管真菌颗粒载体已受到关注,但其在木糖醇生产中的应用仍未得到探索。在本研究中,使用酵母菌株WC 1507生产木糖醇。在游离细胞培养中,在pH高于3.5、低氧含量以及含有(NH₄)₂SO₄和酵母提取物作为氮源的培养基条件下观察到最佳条件(木糖醇产量为79.4 g/L,产率为66.3%,体积生产率为1.3 g/L/h)。使用无活性的颗粒菌丝体载体(MC)和海藻酸钠珠(AB)固定酵母细胞,并在烧瓶中连续进行三轮生产运行进行测试。此外,还研究了在载体外表面涂覆0.2% w/v海藻酸钠层(分别为cMC和cAB)的效果。虽然固定化细胞和游离细胞的产率值相似,但固定化细胞的最终木糖醇产量和体积生产率较低,这可能是由于传质限制所致。AB和cAB的表现优于MC和cMC。未涂覆的AB载体在实验室规模的气升式生物反应器中进行了测试,结果表明在重复分批过程中木糖醇产量逐渐增加:在第三次运行中,木糖醇产量达到63.0 g/L,产率为61.5%,体积生产率为0.52 g/L/h。本研究证实WC 1507在游离细胞和固定化细胞系统中都是生产木糖醇的有前景的菌株。考虑到野生菌株的性能,进行代谢工程干预以进一步提高木糖醇生产效率是合理的。MC和AB被证明是可行的细胞固定化载体,但需要进一步的工艺开发来确定最佳的生物反应器配置和发酵条件。