Disentangling de-novo synthesis, recycling and transformation of nalkyl lipids in soils by combination of position-specific 13C labeling with fragment-specific 13C analysis
Related persons:Lipids represent one of the most diverse classes of biomolecules and
have various functions: main component of cell membranes,
protection layers, storage compounds, etc. High diversity and unique
speciation of lipids in plant and microbial taxonomic groups made
them to one of the most promising biomarker classes in soils and
sediments. They are an important component of soil organic matter
(SOM) and contribute to physico-chemical properties like
hydrophobicity and C storage. Detailed knowledge on lipid sources
exists from studies using lipids as biomarkers, but lipid
transformations in soils are nearly unknown. Recycling is assumed to
be a highly relevant process in soils as lipids are expensive
compounds for de-novo synthesis, but is not proven in-situ, yet. This
proposal aims at disentangling microbial transformation of lipid
precursors, de-novo synthesis of microbial lipids and recycling of
lipids in soil to yield new insights into the network of processes
underlying the lipid cycle and to deepen our understanding of SOM
transformations. Lipid de-novo synthesis in microbial cells will be
investigated by application of 13C glucose, a precursor, which is
quickly taken up by microorganisms. Fragment-specific 13C
incorporation based on liquid chromatography-mass spectrometry
with online fragmentation will enable to separate de-novo synthesis of
phospholipid headgroups, backbone and fatty acid alkyl chains. In
addition to intracellular de-novo synthesis, lipid recycling from
extracellular pools will be investigated. Position-specifically labeled
palmitate (13C-1, 13C-2, 13C-16) will be applied to soil and
incorporation into microbial phospholipids fatty acids (PLFA) will be
analyzed by gas chromatography-mass spectrometry with online
fragmentation. Thus, intact incorporation of the added n-alkyl chain
into PLFA will reveal recycling of free lipids from soils. The sum of
extra- and intracellular transformations of lipids on a medium-term
time scale (4 years) will be studied using position-specifically 13C
labeled palmitate in an already established field experiment.
Recycling and transformations of the n-alkyl chain will be followed into
various n-alkyl lipids (n-alkanes, n-alcohols, n-fatty acids, hydroxy
fatty acids) of the extractable lipid and hydrolyzable lipid pools.
Combining position-specific labeling with fragment-specific 13C
incorporation analysis gives us a unique perspective on lipid
transformations in soil: Recycling can be unambiguously differentiated
from de-novo synthesis in soils in-situ. Distinguishing recycling from
stabilization is crucial in understanding the soil C cycle. Such
identification of microbial transformations during lipid recycling will
strongly improve our interpretation of plant and microbial lipid
biomarker fingerprints and deepen our understanding on turnover of
one of the major substance classes of SOM.