Journal
ORGANIC GEOCHEMISTRY
Volume 139, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.orggeochem.2019.103940
Keywords
Aerobic methanotrophic bacteria; Methylomicrobium; Methane seeps; Stable carbon isotopes; Cyclic terpenoids; Tetrahymanol; Hopanoids; Steroids; Bacteriohopanepolyols
Categories
Funding
- German Academic Exchange Service (DAAD)
Ask authors/readers for more resources
Aerobic methanotrophic bacteria are known to synthesize a variety of cyclic terpenoids which are typified by C-13-depleted, methane-derived carbon. This peculiarity facilitates identification of methanotroph biomarkers in natural samples. However, the current biomarker database does not always allow biomarker patterns of marine samples to be assigned to the different types of aerobic methanotrophs. To overcome this shortcoming, the carbon stable isotope composition of cyclic terpenoids of two strains of the Type I methanotroph genus Methylomicrobium was analyzed. Other than aerobic methanotrophs used for biomarker studies in the past, these two strains deriving from soda lake environments are able to tolerate the conditions typifying marine environments including high alkalinity and salinity. The cyclic terpenoid inventory of the two strains comprises 4-methyl steroids, 3-methyl- and desmethyl bacteriohopanepolyols (aminotetrol and aminotriol), and tetrahymanol, all of which are C-13-depleted. The average carbon isotope fractionation between methane and the respective lipid (Delta delta C-13(terpenoied-methane)) is found to be -25 parts per thousand for M. kenyense and -16 parts per thousand for M. alcaliphilum. These data shed new light on the previously reported compound and carbon stable isotope patterns of cyclic terpenoids from methane-seep environments. Particularly, C-13-depleted tetrahymanol and gammacerane are reinterpreted as biomarkers of aerobic methanotrophic bacteria based on their occurrence in methane-seep deposits in association with other biomarkers of aerobic methanotrophs. The use of delta C-13 values of anaerobic methane-oxidizing archaea (ANME) lipids for the reconstruction of the isotopic composition of parent methane allows us to calculate the Delta delta C-13(terpenoied-methane) even for ancient seep environments. With this calculation, Type I and Type II methanotrophs can be discriminated, representing a new approach to better characterize past methanotrophy at seeps and possibly other marine environments. (C) 2019 Elsevier Ltd. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available