Open AccessEstimating High-Affinity Methanotrophic Bacterial Biomass, Growth, and Turnover in Soil by Phospholipid Fatty Acid 13 C Labeling
Author(s) -
Pete Maxfield,
Edward R. C. Hornibrook,
Richard P. Evershed
Publication year - 2006
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.02779-05
Subject(s) - δ13c , biomass (ecology) , chemistry , soil water , isotopes of carbon , environmental chemistry , stable isotope probing , population , methane , microorganism , stable isotope ratio , bacteria , biology , ecology , total organic carbon , genetics , demography , sociology , physics , quantum mechanics
A time series phospholipid fatty acid (PLFA)13 C-labeling study was undertaken to determine methanotrophic taxon, calculate methanotrophic biomass, and assess carbon recycling in an upland brown earth soil from Bronydd Mawr (Wales, United Kingdom). Laboratory incubations of soils were performed at ambient CH4 concentrations using synthetic air containing 2 parts per million of volume of13 CH4 . Flowthrough chambers maintained a stable CH4 concentration throughout the 11-week incubation. Soils were analyzed at weekly intervals by gas chromatography (GC), GC-mass spectrometry, and GC-combustion-isotope ratio mass spectrometry to identify and quantify individual PLFAs and trace the incorporation of13 C label into the microbial biomass. Incorporation of the13 C label was seen throughout the experiment, with the rate of incorporation decreasing after 9 weeks. The δ13 C values of individual PLFAs showed that13 C label was incorporated into different components to various extents and at various rates, reflecting the diversity of PLFA sources. Quantitative assessments of13 C-labeled PLFAs showed that the methanotrophic population was of constant structure throughout the experiment. The dominant13 C-labeled PLFA was 18:1ω7c, with 16:1ω5 present at lower abundance, suggesting the presence of novel type II methanotrophs. The biomass of methane-oxidizing bacteria at optimum labeling was estimated to be about 7.2 × 106 cells g−1 of soil (dry weight). While recycling of13 C label from the methanotrophic biomass must occur, it is a slower process than initial13 CH4 incorporation, with only about 5 to 10% of13 C-labeled PLFAs reflecting this process. Thus,13 C-labeled PLFA distributions determined at any time point during13 CH4 incubation can be used for chemotaxonomic assessments, although extended incubations are required to achieve optimum13 C labeling for methanotrophic biomass determinations.