Anoxic subseafloor crustal fluids (60-65 °C and pH 7.0-7.3) from Juan de Fuca Ridge (JdFR) flank were used in this study to enrich and potentially isolate anaerobic chemosynthetic hydrogenotrophs driving primary production in these environments. Selective enrichments using H2 as primary electron donor (PED), CO2 or NO3- as terminal electron acceptors (TEA), and CO2 as the carbon (C) source were incubated at temperatures between 65 °C and 75 °C. Cellular morphologies and sizes associated with all cultures tend to vary with incubation times from small cocci to filamentous cells. Similar extensive filamentous, “fungi-like” morphologies containing “spore-like” cells develop at later growth stages under both CO2- and NO3--reducing conditions, suggesting that the same microorganism might be capable of both anaerobic H2-oxidation processes. Microbial transfers made every two weeks for CO2-reducing cultures and three weeks for NO3--reducing cultures reflect shorter doubling times for CO2 reducer OE versus NO3- reducer 34. Additional phylogenetic characterizations will help reveal whether observed morphological similarities are founded on phylogenetic relationships or whether they represent a broader lifestyle adaptation to their crustal subseafloor environment.