oa BHT-x: Constraining its Application as a Lipid Biomarker for Marine Anammox Using a Modern Water-Column Oxygen Gradient

Recently it was discovered that members of the marine anaerobic ammonium oxidizing (anammox) genus, ‘Ca. Scalindua spp.’, uniquely synthesize a stereoisomer of bacteriohopanetetrol (‘BHT-x’). The ratio of BHT-x over total BHT (ubiquitously synthesized by diverse aerobic bacteria) has been suggested as a proxy for water column anoxia. BHT-x hereby has the potential to act as a biomarker for anoxia as well as extend the sedimentary biomarker record of marine anammox. In this study, we have investigated the water column distributions of BHT-x and the BHT-x ratio in suspended particulate matter (SPM) samples at 15 stations along the large oxygen gradient in the Benguela Upwelling System (BUS). Distributions were compared to distributions of intact polar (IPL) ladderane phospholipids, ladderane fatty acids (FAs) and the presence of the Ca. Scalindua 16S rRNA gene reads. The similar distributions of BHT-x, ladderane FAs and the relative abundance of Ca. Scalindua 16S rRNA genes confirms the suitability of BHT-x as a biomarker for water column anammox in the sedimentary record of upwelling systems. Nevertheless, we suggest including the BHT-x ratio when interpreting anammox based on lipid biomarkers, as this study confirms that low abundance of BHT-x may not always reflect in situ water column anammox.