title: Geochemically distinct carbon isotope distributions in Allochromatium vinosum DSM 180Tgrown photoautotrophically and photoheterotrophically.
abstract: Anoxygenic, photosynthetic bacteria are common at redox boundaries. They are of interest in microbial ecology and geosciences through their role in linking the carbon, sulfur, and iron cycles, yet much remains unknown about how their flexible carbon metabolism-permitting either autotrophic or heterotrophic growth-is recorded in the bulk sedimentary and lipid biomarker records. Here, we investigated patterns of carbon isotope fractionation in a model photosynthetic sulfur-oxidizing bacterium, Allochromatium vinosum DSM180T. In one treatment, A. vinosum was grown with CO2as the sole carbon source, while in a second treatment, it was grown on acetate. Different intracellular isotope patterns were observed for fatty acids, phytol, individual amino acids, intact proteins, and total RNA between the two experiments. Photoautotrophic CO2fixation yielded typical isotopic ordering for the lipid biomarkers: δ13C values of phytol > n-alkyl lipids. In contrast, growth on acetate greatly suppressed intracellular isotopic heterogeneity across all molecular classes, except for a marked13C-depletion in phytol. This caused isotopic "inversion" in the lipids (δ13C values of phytol < n-alkyl lipids). The finding suggests that inverse δ13C patterns of n-alkanes and pristane/phytane in the geologic record may be at least in part a signal for photoheterotrophy. In both experimental scenarios, the relative isotope distributions could be predicted from an isotope flux-balance model, demonstrating that microbial carbon metabolisms can be interrogated by combining compound-specific stable isotope analysis with metabolic modeling. Isotopic differences among molecular classes may be a means of fingerprinting microbial carbon metabolism, both in the modern environment and the geologic record.
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.|State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China.
authors.forename: T
authors.initials: T
authors.lastname: Tang
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.|Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Mohr
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Sattin
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.|Department of Chemistry, Stonehill College, Easton, MA, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Rogers
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
authors.forename: P R
authors.initials: PR
authors.lastname: Girguis
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Pearson
mesh_terms: D000085:Acetates / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis*; D002841:Chromatiaceae / Q000737:chemistry* / Q000254:growth & development* / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D010836:Phytol / Q000032:analysis; D011506:Proteins / Q000032:analysis; D012329:RNA, Bacterial / Q000032:analysis
chemical_list: D000085:Acetates; D000596:Amino Acids; D002247:Carbon Isotopes; D005227:Fatty Acids; D011506:Proteins; D012329:RNA, Bacterial; D002245:Carbon Dioxide; D010836:Phytol