IF EXTANT EXTRATERRESTRIAL LIFE EXISTS IT LIKELY RESIDES IN A SUBSURFACE ENVIRONMENT. THE SUBSURFACE OFFERS PROTECTION FROM SURFICIAL ENVIRONMENTAL STRESSORS AND LITHOTROPHIC ENERGY SOURCES FROM ROCKS AND FLUIDS. BIOFILM FORMATION ON MINERAL SURFACES IS A COMMON ECOLOGICAL NICHE IN SUBSURFACE SYSTEMS AND MAY THEREFORE BE AN IMPORTANT SURVIVAL MECHANISM. GIVEN THE CRITICAL ROLE THAT BIOFILM FORMATION MAY PLAY IN DEEP SUBSURFACE SURVIVAL IT IS IMPERATIVE TO CHARACTERIZE THE DISTRIBUTION PHYLOGENY AND METABOLIC STRATEGIES OF DEEP BIOFILM COMMUNITIES TO INFORM THE HABITABILITY OF OTHER PLANETARY BODIES. THIS PROPOSAL SEEKS TO INVESTIGATE PHYSIOLOGICAL ADAPTATION TO LIFE ON MINERAL SURFACES OF DEEP FRACTURE-HOSTED BIOFILMS IN AN EXTRATERRESTRIAL ANALOG SITE CALLED THE DEEP MINE MICROBIAL OBSERVATORY (DEMMO). PREVIOUS THERMODYNAMIC PREDICTIONS ABOUT FAVORABLE MICROBIAL METABOLISMS BY OSBURN ET AL. 2014 MOTIVATED OUR PILOT STUDY WITH FLOW-THROUGH IN SITU CULTIVATION EXPERIMENTS USING IRON SULFUR AND MANGANESE-BEARING MINERALS AT TWO DEMMO SITES LOCATED AT DEPTHS OF 610 AND 1 480 METERS. THE IN SITU CULTIVATION EXPERIMENTS WERE DESIGNED TO PROMOTE BIOFILM COLONIZATION ON MINERAL SURFACES OVER TWO MONTHS WHICH WERE THEN HARVESTED AND USED TO INOCULATE BATCH CULTIVATION EXPERIMENTS IN THE LABORATORY. THE COMPELLING PILOT STUDY RESULTS INVITE FURTHER INVESTIGATION OF BIOFILM COMMUNITIES AT DEMMO. HERE I PROPOSE ADDITIONAL ANALYSES ON PILOT STUDY BIOFILMS NEW IN SITU CULTIVATION EXPERIMENTS TO BROADEN THE INVESTIGATED RANGE OF SUBSURFACE CONDITIONS AND MINERALS AND LABORATORY-BASED CULTIVATION EXPERIMENTS GUIDED BY THERMODYNAMIC METABOLISM MODELING TO TARGET ISOLATION OF REPRESENTATIVE DEMMO BIOFILM COMMUNITY MEMBERS. THE COMPLEMENTARY FIELD AND LABORATORY-BASED DATA WILL LINK PHYLOGENY TO METABOLISM IN THIS EXTRATERRESTRIAL ANALOG SETTING PROVIDING INSIGHT INTO PHYSIOLOGICAL ADAPTATION STRATEGIES THAT MAY BE CRITICAL TO SUBSURFACE SURVIVAL AND INFORMING HABITABILITY OF OTHER PLANETS.