Comprehensive profiling of the metabolome in corn silage inoculated with or without <i>Lactiplantibacillus plantarum</i> using different untargeted metabolomics analyses
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Silage fermentation is a complicated biochemical process involving interactions between microbes and metabolites. However, the overall metabolome feature of ensiled forage and its response to lactic acid bacteria inoculation is poorly understood. Hence, in this study metabolome profiles of whole-plant corn silage inoculated with or without <i>Lactiplantibacillus plantarum</i> were characterised via solid-phase microextraction/gas chromatography/mass spectrometry (SPME-GC-MS), gas chromatography/time-of-flight mass spectrometry (GC-TOF-MS), and Liquid chromatography/Q Exactive HFX mass spectrometry (LC-QE-MS/MS) analysis. There were 2087 identified metabolites including 1143 reliably identified metabolites in fresh and ensiled whole-plant corn. After ensiling, the increased metabolites in whole-plant corn were mainly composed of organic acids, volatile organic compounds (VOC), benzene and substituted derivatives, carboxylic acids and derivatives, fatty acyls, flavonoids, indoles and derivatives, organooxygen compounds (including amines and amides), phenols, pyridines and derivatives, and steroids and steroid derivatives, which includes neurotransmitters and metabolites with aromatic, antioxidant, anti-inflammatory, and antimicrobial activities. Phenylacetaldehyde was the most abundant aromatic metabolite after ensiling. L-isoleucine and oxoproline were the major free amino acids in silage. Ensiling markedly increased the relative abundances of 3-phenyllactic acid, chrysoeriol, 6-O-acetylaustroinulin, acetylcholine, γ-aminobutyric acid, pyridoxine, and alpha-linoleic acid. Inoculation with <i>L. plantarum</i> remarkably changed silage VOC composition, and essential amino acids, 3-phenyllactic acid, and cinnamaldehyde compared with untreated silage. The present study does not only provide a deeper insight into metabolites of the ensiled whole-plant corn but also reveals metabolites with specific biological functions that could be much helpful in screening novel lactic acid bacteria to well ensile forages. Inoculation with <i>L. plantarum</i> significantly affects the metabolome in ensiled whole-plant corn.
青贮发酵是一类涉及微生物与代谢物相互作用的复杂生化过程。然而，当前学界对青贮饲草的整体代谢组（metabolome）特征及其对乳酸菌接种的响应机制仍缺乏深入认知。因此，本研究通过固相微萃取-气相色谱-质谱联用法（SPME-GC-MS）、气相色谱-飞行时间质谱联用法（GC-TOF-MS）及液相色谱/Q Exactive HFX质谱联用法（LC-QE-MS/MS）三种分析手段，对接种与未接种植物乳杆菌（Lactiplantibacillus plantarum）的全株玉米青贮的代谢组特征进行了表征。本研究共鉴定出2087种代谢物，其中新鲜与青贮全株玉米中共可靠鉴定出1143种代谢物。青贮后，全株玉米中丰度上调的代谢物主要涵盖有机酸、挥发性有机化合物（VOC）、苯及其取代衍生物、羧酸及其衍生物、脂肪酰类、黄酮类、吲哚及其衍生物、有机氧化合物（包含胺类与酰胺类）、酚类、吡啶及其衍生物以及甾体及其衍生物；上述代谢物涵盖神经递质，以及具有芳香性、抗氧化、抗炎及抗菌活性的代谢物。苯乙醛是青贮后含量最高的芳香族代谢物。L-异亮氨酸与氧代脯氨酸是青贮饲料中的主要游离氨基酸。青贮过程显著提升了3-苯基乳酸、金圣草黄素、6-O-乙酰基Austroinulin、乙酰胆碱、γ-氨基丁酸、吡哆醇及α-亚麻酸的相对丰度。与未接种处理的青贮饲料相比，接种植物乳杆菌可显著改变青贮饲料的挥发性有机化合物组成，以及必需氨基酸、3-苯基乳酸与肉桂醛的相对含量。本研究不仅加深了对青贮全株玉米代谢物的认知，还揭示了一批具有特定生物学功能的代谢物，可为筛选可实现优质青贮饲草的新型乳酸菌提供重要参考。接种植物乳杆菌可显著影响青贮全株玉米的代谢组特征。
