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A unique bacteriohopanetetrol stereoisomer of marine anammox
Résumé
Anaerobic ammonium oxidation (anammox) is a major process of bioavailable nitrogen removal frommarine systems. Previously, a bacteriohopanetetrol (BHT) isomer, with unknown stereochemistry, eluting
later than BHT when examined by high performance liquid chromatography (HPLC), was detected
in ‘Ca. [voir la suite] Scalindua profunda’ and proposed as a biomarker for anammox in marine paleo-environments.
However, the utility of this BHT isomer as an anammox biomarker is hindered by the fact that four other,
non-anammox, bacteria are also known to produce a late-eluting BHT stereoisomer. The stereochemistry
in Acetobacter pasteurianus, Komagataeibacter xylinus and Frankia sp. was known to be 17b, 21b(H), 22R,
32R, 33R, 34R (BHT-34R). The stereochemistry of the late-eluting BHT in Methylocella palustris was
unknown. To determine if marine anammox bacteria produce a unique BHT isomer, we studied the
BHT distributions and stereochemistry of known BHT isomer producers and of previously unscreened
marine (‘Ca. Scalindua brodeae’) and freshwater (‘Ca. Brocadia spp.’) anammox bacteria, using HPLC
and gas chromatographiy (GC) analysis of acetylated BHTs and ultra high performance liquid chromatography
(UHPLC)-high resolution mass spectrometry (HRMS) analysis of non-acetylated BHTs. The 34R
stereochemistry was confirmed for the BHT isomers in Ca. Brocadia sp. and Methylocella palustris.
However, ‘Ca. Scalindua spp.’ synthesises a stereochemically distinct BHT isomer, with still unconfirmed
stereochemistry (BHT-x). Only GC analysis of acetylated BHT and UHPLC analysis of non-acetylated BHT
distinguished between late-eluting BHT isomers. Acetylated BHT-x and BHT-34R co-elute when examined
by HPLC. As BHT-x is currently only known to be produced by ‘Ca. Scalindua spp.’, it may be a biomarker
for marine anammox.