Award: OCE-1521614

The oceanic crust constitutes a vast aquifer of circulating fluids and represents a significant, but relatively unexplored biosphere. Observations of crustal fluids sampled from the eastern flank of the Juan de Fuca Ridge (JFR) have revealed an abundance of motility and chemotactic genes. Motility is viewed as an energy expensive function and generally thought to be impractical for organisms surviving in energy-starved environments. Thus, the objective of this study was to search for and identify the microorganisms capable of motility and to characterize their motile behavior to evaluate how motility may be used as a strategy for life in crustal fluids. Using existing genomic datasets as a guide, enrichment cultures containing motile organisms were established from crustal fluids of the JFR. These cultures represent a prime example of how genomic interpretations can be utilized to determine nutrient requirements for laboratory growth. A motile organism of this enrichment was isolated and represents the first organism to be isolated directly from the subsurface crustal fluids of the JFR, and thus, the physiological observations of this study are the first steps towards understanding life in the oceanic crust. The organism was classified as belonging to the genus Thalassospira. We identified phosphate as a chemical attractant for the Thalassospira organism; phosphate is a requirement for growth and is a limiting nutrient in the crustal biosphere. The presence or absence of phosphate in the growth media changed the morphology and motile behavior of the organism. When phosphate was added to the medium (> 50 µM), Thalassospira cells were cocci shaped, approximately 1 µM in diameter. When phosphate was excluded from the medium, cells became elongated and spirillum-shaped, growing up to 10 µM in length. This behavior has previously been observed with planktonic isolates. However, unlike previous planktonic descriptions, we also noted biofilm production when Thalassospira was grown in the presence of phosphate for long periods of time. We hypothesized that biofilm production might be used to adhere to favorable substrates, while motility is used to move on when conditions become less favorable. To test Thalassospira?s ability to forage and adhere to favorable substrates, Thalassospira organisms were grown in the presence of phosphate-bearing basalt rocks and basalt rocks without phosphate. Initial results suggest that the Thalassospira organisms grew faster and to higher concentrations in the presence of phosphate-bearing basalt rocks. To confirm these results, replicate experiments are being conducted at Hartwick College by PI Carr and Hartwick College undergraduate students. Together, Dr. Carr and the students are developing new methods to quantify and image biofilms on crustal materials. While our understanding of this crustal Thalassospira species is still preliminary, the observed motility and potentially active foraging in laboratory settings suggests that these behaviors may also occur in the crustal biosphere. Future investigations relating to how microorganisms might budget for these energy-expensive behaviors will improve our understanding of microbial life in the deep biosphere, and other extreme environments. Additionally, understanding potential foraging and substrate consumption (metabolic rates) in the crustal subsurface—an environment that covers 70% of our globe—will advance the knowledge of biogeochemical cycles on a global scale. Last Modified: 11/30/2017 Submitted by: Stephanie A Carr