Influence of Microbial Membranes on Biofilm Formation, Scaling Reactions, and Production Chemistry in Engineered Energy Systems (Final Report)
Humans are engineering the deep subsurface for the purposes of energy-capture, energy-storage, and environmental mitigation. Despite the potential for microbial communities to significantly alter the effectiveness of these technologies, we have historically lacked a clear understanding of how microbial cells interact in a fractured shale system. Existing knowledge has been heavily based on genomic information, lacking studies on in situ physiologies, kinetic rates, and attachment mechanisms governing biogeochemical reactions in the system. The overarching goal of this research was to advance understanding of engineered hydrocarbon extraction systems as they evolve from newly developed environments to mature use. Plasma membranes protect microbial cells, mediate many critical functions, and respond to intracellular cues and ecological perturbations through physicochemical modifications. The project objectives were to 1) characterize variables influencing growth and membrane features of shale taxa, 2) characterize the interactions between shale matrices and microorganisms and 3) elucidate engineered and environmental processes driving biogeochemical signatures at the field scale. Objectives were realized through laboratory experiments involving growth of pure cultures and enrichments in continuous culture and biofilms; access to samples from two DOE-NETL funded energy-capture sites: Marcellus Shale Energy and Environmental Laboratory (MSEEL and MSEEL II); and through collaborations with scientists and engineers at the Environmental Molecular Science Laboratory (EMSL) and National Energy Technology Laboratory (NETL). Key findings showed (a) Halanaerobium congolense WG10 makes its membrane more fluid and thicker through increasing its polyunsaturated fatty acid (PUFA) composition under non-optimal salinities (7% and 20%) compared to the optimum (13% NaCl); (b) anionic phospholipids within the plasma membrane are important for high salinity tolerance in H. congolense WG10 while zwitterionic species modulate biofilm physiologies in both isolate and mixed cultures, and (c) tyrosine accumulation with overexpression of Na+/H+ antiporters are essential for osmoprotection in H. congolense WG10 under high salinity while upregulation of aromatic amino acid synthesis and cell envelope maintenance underpin biofilm formation. It is clear from these results that microbial persistence in fractured shale reservoirs under environmental and engineered perturbations requires strategic plasma membrane lipid chemistry adjustments and metabolic restructuring, with implications for improved shale microbiology management and more efficient hydrocarbon extraction approaches targeting microorganisms.