Potential microbial contamination from drilling lubricants into subseafloor rock cores

Abstract

Abstract. International Ocean Discovery Program (IODP) Expedition 357: “Serpentinization and Life” drilled shallow cores into the Atlantis Massif near the Mid-Atlantic Ridge in October 2015 using seabed drills. Serpentinization and other geochemical processes occurring within the Atlantis Massif release hydrogen, methane, and other chemicals that can potentially fuel microorganisms through chemosynthesis. The subseafloor rock cores collected during IODP Exp. 357 are the first of their kind, meaning the analysis and interpretation of these samples required new methodologies, including a specialized approach for distinguishing endemic subsurface inhabitants from potential contaminants from various sources. Background samples of various potential contamination sources were collected during sampling: 109 samples of seawater collected before, during, and after drilling; 20 samples of greases and oils associated with the drilling equipment; and samples of the laboratory's ambient air. Despite the widespread usage of drilling lubricants and the importance of controlling contamination in drill-core samples for microbiological analyses, no studies to date have looked at DNA in drilling greases and oils. In this study, drilling lubricants were analyzed as possible sources of microbial contamination of subseafloor rock core samples by environmental sequencing of 16S rRNA genes. We find that microbial signatures from drilling lubricants are only found in low abundance in seafloor samples (at most a few percent of total sequence counts), with laboratory contaminants being a greater source of contamination.

Expedition 399 Preliminary Report: Building Blocks of Life, Atlantis Massif

“…Insights into the constraints on life in the subseafloor and the metabolic strategies that the small numbers of inhabitants employ can be gained in part through characterization of the endolithic communities. Distinguishing endemic microbial taxa from those introduced from seawater or contamination is a major challenge requiring multiple strategies to overcome (Kallmeyer, 2017;Sylvan et al, 2021;Pendleton et al, 2021). Nonetheless, the signatures of endolithic communities have been successfully identified from the subseafloor of the Atlantis Massif during both Expeditions 304 (Mason et al, 2010) and 357 (Motamedi et al, 2020;Goordial et al, 2021;Quéméneur et al, 2019) (Figure F9).…”

Expedition 399 Scientific Prospectus: Building Blocks of Life, Atlantis Massif

“…Insights to the constraints on life in the subseafloor and the metabolic strategies that the small numbers of inhabitants employ can be gained in part through characterization of the endolithic communities. Distinguishing endemic microbial taxa from those introduced from seawater or contamination is a major challenge requiring multiple strategies to overcome (Kallmeyer et al, 2017;Sylvan et al, 2021;Pendleton et al, 2021). Nonetheless, the signatures of endolithic commu- nities have been successfully identified from the subseafloor of the Atlantis Massif during both Expeditions 304 (Mason et al, 2010) and 357 (Motamedi et al, 2020;Goordial et al, 2021;Quéméneur et al, 2019) (Figure F11).…”