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https://doi.org/10.5194/bg-2020-349
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-349
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  30 Oct 2020

30 Oct 2020

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This preprint is currently under review for the journal BG.

Novel hydrocarbon-utilizing soil mycobacteria synthesize unique mycocerosic acids at a Sicilian everlasting fire

Nadine T. Smit1, Laura Villanueva1, Darci Rush1, Fausto Grassa2, Caitlyn R. Witkowski1, Mira Holzheimer3, Adriaan J. Minnaard3, Jaap S. Sinninghe Damsté1,4, and Stefan Schouten1,4 Nadine T. Smit et al.
  • 1NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, P.O. Box 59, 1790 Ab Den Burg Texel, the Netherlands
  • 2Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa, 153, 90144, Palermo, Italy
  • 3Stratingh Institute for Chemistry, University of Groningen, 9747 AG Groningen, the Netherlands
  • 4Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80.121, 3508 TA Utrecht, the Netherlands

Abstract. Soil bacteria rank among the most diverse groups of organisms on Earth and actively impact global processes of carbon cycling, especially in the emission of greenhouse gases like methane, CO2 and higher gaseous hydrocarbons. An abundant group of soil bacteria are the mycobacteria, which colonize various habitats due to their impermeable cell envelope that contains remarkable lipids. These bacteria have been found to be highly abundant at petroleum and gas seep areas, where they might utilize the released hydrocarbons. However, the function and the lipid biomarker inventory of these soil mycobacteria are poorly studied. Here, soils from the Fuoco di Censo seep, an everlasting fire (gas seep) in Sicily, Italy, were investigated for the presence of mycobacteria via 16S rRNA gene sequencing and fatty acid profiling. The soils contained high relative abundances (up to 34 % of reads assigned) of mycobacteria, phylogenetically close to the Mycobacterium simiae complex and more distant to the well-studied M. tuberculosis and hydrocarbon-utilizing M. paraffinicum. The soils showed decreasing abundances of mycocerosic acids (MAs), fatty acids unique for mycobacteria, with increasing distance from the seep. The major MAs at this seep were tentatively identified as 2,4,6,8-tetramethyl tetracosanoic acid and 2,4,6,8,10-pentamethyl hexacosanoic acid. Unusual MAs with mid-chain methyl branches at positions C-12 and C-16 (i.e. 2,12-dimethyl eicosanoic acid and 2,4,6,8,16-pentamethyl tetracosanoic acid) were also present. The molecular structures of the Censo MAs are different from those of the well-studied mycobacteria like M. tuberculosis or M. bovis and have relatively 13C-depleted values (−38 to −48 ‰), suggesting a direct or indirect utilization of the released seep gases like methane or ethane. The structurally unique MAs in combination with their depleted δ13C values identified at the Censo seep offer a new tool to study the role of soil mycobacteria as hydrocarbon gas consumers in the carbon cycle.

Nadine T. Smit et al.

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Nadine T. Smit et al.

Nadine T. Smit et al.

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Short summary
Soils from an everlasting fire (gas seep) in Sicily, Italy reveal high relative abundances of novel uncultivated mycobacteria and unique 13C depleted mycocerosic acids (multi-methyl branched fatty acids) close to the main gas seep. Our results imply, that mycocerosic acids in combination with their depleted δ13C values offer a new biomarker tool to study the role of soil mycobacteria as hydrocarbon consumers in the modern and past global carbon cycle.
Soils from an everlasting fire (gas seep) in Sicily, Italy reveal high relative abundances of...
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