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

Abstract

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-HRMS² 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.