Project: OCE-PRF Track 1: Resolving the Advantages of Motility and Chemotaxis in Oceanic Crust

NSF Award Abstract

The oceanic crust constitutes a vast aquifer of circulating fluids and represents a significant, but relatively unexplored biosphere. Genomic 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. The goal of this project is to investigate the chemotactic potential of these unique subsurface organisms, leveraging the aforementioned genomic datasets to enable the isolation and detailed study of motile microorganisms in the laboratory. The expected significance of this project will be the fundamental understanding of adapted strategies of microbial life in subsurface oceanic crust, which will further impact interpretations of biogeochemical cycling in this vast environment. Outreach efforts include training undergraduate students from underrepresented groups in STEM in novel genomic techniques and sharing results with the public at community seminars and through K-12 educational projects.

Motility is viewed as an energy expensive function and impractical for organisms surviving in energy starved environments. Nevertheless, enrichment cultures have already been established from crustal fluids of the JFR based on genomic data and metabolic interpretations. Microscopy confirms the presence of active motile organisms within these enrichments. These cultures represent a prime example of how genomic interpretations can be utilized to determine nutrient requirements for laboratory growth. The objectives of this study include (1) isolating motile cells in pure culture, and sequencing the genomes of these pure isolates in order to recognize their metabolic potential within crustal environments. Given that these enrichment cultures are some of the first to be successfully grown from subsurface crustal fluids, any physiological or metabolic observations will be novel and important for understanding life in the oceanic crust. The second objective is to (2) investigate which chemical attractants are most attractive to the cultures isolated in objective 1. Chemotactic response will be observed within gradient tubes filled with 0.15% low-melt agarose containing hard agar nutrient plugs. Chemotactic responses will be evaluated as growth towards or away from the hard chemoattractant plug. The final objectives of this study are to measure the rates of nutrient consumption by crustal fluid organisms, their average and maximum speeds, and their reaction time to nutrients under (3) optimal growth conditions and (4) in situ JFR nutrient conditions. Motility will be studied using a custom microfluidic microscope slide. Micro-channels of this slide will be filled with the various nutrient attractants determined from objectives 1 and 2. Cell behavior and motility towards attractants will be monitored using an inverted brightfield microscope and digitally recorded to calculate and model 2D velocities. Collectively, this suite of independent, yet complementary, laboratory and genomic analyses are aimed to better understand the role of motility in the oceanic crust, ultimately resolving unique adaptations for survival in this environment and advancing the knowledge of geochemical cycles in oceanic crust.