Occurrence of nucleoside-bacteriohopanepolyol in high latitude soils: evidence of environmental controls on bacterial lipid membrane distributions

Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS2) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS2direct analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ~800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R2 = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.

近年来，通过超高效液相色谱-高分辨质谱（UHPLC-HRMS²）对未衍生化细菌藿烷多醇（BHPs）开展的分析，揭示了该脂质类化合物拥有广泛的结构多样性。研究人员在土壤中鉴定出多种带有核苷型极性头部基团的独特细菌藿烷多醇（Nu-BHPs）。此前虽已在土壤有机质中以高丰度检出Nu-BHPs，但仅能通过分析乙酰化细菌藿烷多醇实现，这一局限阻碍了其结构解析。本研究首次将超高效液相色谱-高分辨质谱直接分析方法应用于土壤样带，以重新探究Nu-BHPs的分布特征、环境依赖性及其代用指标潜力。我们对阿拉斯加北部约800公里样带沿线的17个表层土壤样品中的Nu-BHPs存在情况与分布特征进行了检测。结果显示，部分Nu-BHPs与温度、土壤pH值等环境参数存在显著相关性。本研究通过构建新型比值参数实现了9种Nu-BHPs的变异度表征，并采用线性回归方法建立了最热季土壤温度（WQST）的区域校准模型（决定系数R²=0.72）。针对夏季气温与年平均气温建立的其他校准模型同样表现出较强的正相关关系。鉴于BHPs在全球土壤中普遍存在，本研究凸显了以Nu-BHPs为基础建立校准模型，以补充现有土壤pH值与温度有机代用指标（如分支四醚脂类（branched tetraether lipids））的潜在价值。不过，这类BHPs的环境依赖性背后的分子机制仍未明确。未来应开展进一步研究以探究其代用指标潜力以及这类脂质的细菌来源，例如沿土壤pH值与温度相关梯度开展土壤采样工作。