Analysis of transcriptomic response to SO2 by Oenococcus oeni growing in a continuous culture

To successfully complete malolactic fermentation (MLF), Oenococcus oeni must overcome wine stress conditions of low pH, high ethanol, and presence of SO2. Failure to complete MLF may result in detrimental effects to the quality and stability of the resulting wines. Research efforts to date have focused on elucidating the mechanisms and genetic features that confer the ability to withstand low pH and high ethanol concentrations on O. oeni, however, the responses to SO2 stress are less well defined. This study focused on characterizing the transcriptional response of O. oeni to SO2 challenge during cultivation in a continuous system at wine-like pH (3.5). This experimental design allowed the precise discrimination of transcriptional changes linked to SO2 stress from responses associated to growth stage and cultivation parameters. Differential gene expression analysis revealed major transcriptional changes following SO2 exposure and suggested that this compound primarily interacts with intracellular proteins, DNA and the cell envelope of O. oeni. The molecular chaperone hsp20, which has a demonstrated function in the heat, ethanol and acid stress response, was highly upregulated, confirming its additional role in the response of this species to SO2 stress. This work also reports the first nanopore-based complete genome assemblies for O. oeni.

为顺利完成苹果酸-乳酸发酵（malolactic fermentation, MLF），酒酒球菌（Oenococcus oeni）必须克服葡萄酒环境中的低pH、高乙醇及二氧化硫（SO2）胁迫条件。若无法完成该发酵过程，将会对成品葡萄酒的品质与稳定性产生不利影响。迄今为止，相关研究多聚焦于阐明酒酒球菌抵御低pH与高乙醇胁迫的分子机制及遗传特征，但针对其应对二氧化硫胁迫的响应机制，目前尚未被充分阐明。本研究以在模拟葡萄酒pH（3.5）的体系中进行连续培养的酒酒球菌为对象，解析其受二氧化硫胁迫时的转录响应。该实验设计可精准区分由二氧化硫胁迫引发的转录变化，与生长阶段及培养参数相关的转录应答。差异基因表达分析（differential gene expression analysis）结果显示，酒酒球菌暴露于二氧化硫后发生了显著的转录组变化，且该化合物主要与酒酒球菌的胞内蛋白、DNA及细胞被膜发生相互作用。此前已被证实可参与热、乙醇及酸胁迫响应的分子伴侣（molecular chaperone）热休克蛋白20（hsp20）在本研究中呈现显著上调，证实了其在酒酒球菌应对二氧化硫胁迫过程中的额外作用。本研究同时首次报道了基于纳米孔（nanopore）测序技术的酒酒球菌完整基因组组装结果。