BACTERIA, FUNGI AND BIOKARST IN LECHUGUILLA CAVE, CARLSBAD-CAVERNS-NATIONAL-PARK, NEW-MEXICO

Lechuguilla Cave is a deep, extensive, gypsum- and sulfur-bearing hypo genic cave in Carlsbad Caverns National Park, New Mexico, most of whic h (> 90%) lies more than 300 m beneath the entrance. Located in the ar id Guadalupe Mountains, Lechuguilla's remarkable state of preservation is partially due to the locally continuous Yates Formation siltstone that has effectively diverted most vadose water away from the cave. Al locthonous organic input to the cave is therefore very limited, but ba cterial and fungal colonization is relatively extensive: (1) Aspergill us sp. fungi and unidentified bacteria are associated with iron-, mang anese-, and sulfur-rich encrustations on calcitic folia near the suspe cted water table 466 m below the entrance; (2) 92 species of fungi in 19 genera have been identified throughout the cave in oligotrophic (nu trient-poor) ''soils'' and pools; (3) cave-air condensate contains uni dentified microbes; (4) indigenous chemoheterotrophic Seliberius and C aulobacter bacteria are known from remote pool sites; and (5) at least four genera of heterotrophic bacteria with population densities near 5 x 10(5) colony-forming units (CFU) per gram are present in ceiling-b ound deposits of supposedly abiogenic condensation-corrosion residues. Various lines of evidence suggest that autotrophic bacteria are prese nt in the ceiling-bound residues and could act as primary producers in a unique subterranean microbial food chain. The suspected autotrophic bacteria are probably chemolithoautotrophic (CLA), utilizing trace ir on, manganese, or sulfur in the limestone and dolomitic bedrock to mec hanically (and possibly biochemically) erode the substrate to produce residual floor deposits. Because other major sources of organic matter have not been detected, we suggest that these CLA bacteria are provid ing requisite organic matter to the known heterotrophic bacteria and f ungi in the residues. The cavewide bacterial and fungal distribution, the large volumes of corrosion residues, and the presence of ancient b acterial filaments in unusual calcite speleothems (biothems) attest to the apparent longevity of microbial occupation in this cave.