New Mexican Cave Microorganisms Foraging for Nutrients

Nutrient availability is a principal selective pressure within an ecosystem, especially within arid land caves that lack photosynthesis and receive modest nutrient input from the surface. Animal visitation may increase nutrient availability, which could alter microbial community composition and function. One way to measure microbial responses to nutrient availability is to measure extracellular enzyme activity (EEA). To assess EAA, samples were collected from the caves, including soils and ferromanganese deposits (FMD). Four carbonate and four basalt caves were chosen due to their varying temperatures, human visitation frequencies, and geologies. β-1,4-glucosidase (BG), acid phosphatase (AP), and L-alanine aminopeptidase (AAP) activities in soils were measured following published protocols. High human visitation caves had the greatest AP activity (54.1 nmol h^-1g^-1), which is a measure of phosphorus demand. Infrequently visited caves had the highest BG and AAP activities (36.3 and 2.3 nmol h^-1g^-1), indicating higher carbon and nitrogen demand. Carbonate caves had higher BG and AP activities (39.5 and 67.3 nmol h^-1g^-1) than basalt caves (0.7 and 0.1 nmol ^-1g^-1). Preliminary data suggests that phosphorus availability may be the principal limiting factor of microbial EEA activity in caves. Our results suggest that EEA measurements can be used to assess the impact of human activity, as well as other factors, on cave ecology. This research contributes to our understanding of how microorganisms are able to survive in an environment with limited nutrients and betters our understanding of how to protect natural cave microbial communities.