A CENTURY AGO THE CONCEPT OF LITHOTROPHY THE GENERATION OF ENERGY FROM INORGANIC SUBSTRATES DEVELOPED VIA STUDIES ON MICROBIAL OXIDATIONS OF NH3 H2S AND FE(II). EACH OF THESE INVOLVES UNIQUE BIOCATALYSTS INTEGRATED INTO SPECIALIZED ENERGY PATHWAYS OFTEN COUPLED TO CO2 FIXATION INTO BIOMASS. IN BOTH MODERN AND ANCIENT ENVIRONMENTS THESE METABOLISMS HAVE UNDERPINNED GLOBAL BIOGEOCHEMICAL CYCLES OF N S FE AND C IN LARGE PART CONTRIBUTING TO HABITABILITY AS WE KNOW IT. DESPITE RECOGNITION OF THE IMPORTANCE OF LITHOTROPHY LARGE GAPS REMAIN IN OUR KNOWLEDGE OF SOME BIOGEOCHEMICAL CYCLES WHERE LITHOTROPHIC METABOLISMS PRESUMABLY HAVE PLAYED A ROLE. CHIEF AMONG THESE IS THE MN CYCLE. MYSTERIOUS MN(IV) OXIDE NODULES DECORATE THE OCEAN FLOOR AND SIMILARLY ENIGMATIC MN ORE DEPOSITS ARE FOUND NEAR THE BLACK SEA (20 MA) AND THE GOE-ASSOCIATED KALAHARI FIELDS (2.2 GA). HOW DID THEY ARISE? THERMODYNAMIC CALCULATIONS HAVE LONG PREDICTED THAT MN(II) OXIDATION COULD SUSTAIN MICROBIAL GROWTH BUT UNTIL NOW NO ORGANISMS HAVE BEEN REPORTED TO DO SO. SOME BACTERIA ARE KNOWN TO SLOWLY OXIDIZE SMALL AMOUNTS OF MN(II) BUT IN THESE CASES ENERGY IS NOT HARVESTED. THE PI HAS RECENTLY CULTURED THE FIRST KNOWN BACTERIA EXHIBITING UNAMBIGUOUS MN(II)-OXIDATION DEPENDENT GROWTH I.E. IN A DEFINED ENVIRONMENT DEVOID OF OTHER ENERGY SUBSTRATES OR ORGANIC C. RECIPROCALLY RAPID OXIDATION IS DEPENDENT ON THE BACTERIA BEING VIABLE PRODUCING MACROSCOPIC MN(IV) PRECIPITATES. THE CULTURE IS STABLE CAN BE SERIALLY PROPAGATED AND HAS BEEN REFINED TO A 2-SPECIES CONSORTIUM. ORGANISM A NOT YET GROWN ALONE IS NOVEL BEING ONLY VERY DISTANTLY RELATED TO ANY PREVIOUSLY CULTIVATED ORGANISM DESCRIBED. ORGANISM B HAS BEEN ISOLATED ON ANOTHER SUBSTRATE BUT DOESN'T OXIDIZE MN ALONE. THE COMPLETE REFINED GENOME SEQUENCES FOR BOTH SPECIES OF THE CONSORTIUM HAVE RECENTLY BEEN RESOLVED. PRELIMINARY ANALYSIS REVEALS THAT BOTH SPECIES MIGHT FIX CO2 AND THAT BOTH ENCODE UNUSUAL E-TRANSPORT GENE CLUSTERS. A BROAD SPECTRUM OF ANALYSES ON THE BIOLOGY AND MINEROLOGY IS NOW POSSIBLE. OBJECTIVES/APPROACHES. A COMBINATION OF ISOTOPIC GENOMIC TRANSCRIPTOMIC AND EVOLUTIONARY BIOINFORMATIC APPROACHES WILL BE APPLIED TO: 1) DETERMINE IF MN(II) OXIDATION IS COUPLED TO CO2 FIXATION BY THE CONSORTIUM; AND IF SO BY WHICH SPECIES. 2) THOROUGHLY EVALUATE THE SPECIES GENOMES FOR CANDIDATE DETERMINANTS OF MN(II) OXIDATION. MN(II) LITHOTROPHS MUST SOLVE KEY BIOCHEMICAL CHALLENGES NECESSITATING SIGNIFICANT NOVELTIES IN ELECTRON TRANSPORT E.G. ACTIVATING LOUSY HIGH POTENTIAL ELECTRONS FOR RESPIRATION AND CO2 FIXATION AND DEALING WITH THE PRODUCTION OF A METAL OXIDE SOLID THAT MUST EITHER BE TRANSPORTED OR GENERATED OUTSIDE OF THE CELL. 3) ANALYZE THE TRANSCRIPTOMES OF STRAIN A GROWN IN THE MN(II) OXIDIZING CONSORTIUM WITH STRAIN B AND THE LATTER GROWN ALONE ON SEVERAL ALTERNATIVE SUBSTRATES. COMPARATIVE ANALYSIS WILL REVEAL GENES UNIQUELY EXPRESSED DURING MN(II) OXIDATION. 4) PERFORM EVOLUTIONARY AND PHYLOGENETIC ANALYSES ON CANDIDATE GENES PUTATIVELY UNDERLYING THE NOVEL PHYSIOLOGY. SIGNIFICANCE. THIS NEW LINE OF INQUIRY WILL PROVIDE KEY INSIGHTS INTO THE MOLECULAR BASIS OF A LONG-SOUGHT LITHOTROPHIC METABOLISM PROVIDING A FOUNDATION FOR FUTURE STUDIES. KNOWLEDGE GENERATED THROUGH THIS WORK ULTIMATELY PROMISES TO INFORM THE INTERPRETATION OF LARGE MN(IV) OXIDE DEPOSITION EVENTS ON THE EARLY EARTH. THIS RESEARCH IS SPECIFICALLY RESPONSIVE TO THE EARLY EVOLUTION OF LIFE AND THE BIOSPHERE (POINTS II IV AND VII) EMPHASIS OF THIS CALL AS WELL AS THE 2015 ASTROBIOLOGY STRATEGY SECTIONS 4.4.III AND 7.1.IV (PP 70; 81- 88 147). LASTLY THE REDUCTION OF MN(IV) AS A GROWTH-PROMOTING RESPIRATORY OXIDANT BY ANAEROBES DISCOVERED 30 YEARS AGO INTERSECTS WITH AND IS RELEVANT TO OTHER BIOGEOCHEMICAL CYCLES. IMPLICIT TO THE FINDINGS UNDERLYING THIS PROPOSAL: A NOVEL COMPLETE AND HERETOFORE UNRECOGNIZED MICROBIAL-ENERGETICS-DRIVEN MN REDOX CYCLE MUST NOW BE ENTERTAINED.