Human urine in Lechuguilla Cave: the microbiological impact and potential for bioremediation

Abstract

During extended exploration trips in caves, it is sometimes not possible to remove all excreted urine due to its volume and weight. Excess urine can be particularly problematic in dry caves where, without dilution, urine introduces a significant source of nitrogen into these otherwise nitrogen-limited environments. It was the aim of this study to determine the impact that human urine could have on cave microbiota over an extended period of time. To do this, we examined the microbial community structure of a heavily impacted site in Lechuguilla Cave, USA. Using a molecular phylogenetic approach we generated a 136-member 16S rRNA clone library that demonstrated representatives of the Alpha-Beta-and Gammaproteobacteria, the Bacteroidetes, Firmicutes, Actinobacteria and Deinococcus-Thermus group at this site. The structure of the microbial community at the impacted site suggests that it is colonized by endemic cave species rather than human commensal organisms, while metabolic inference suggests that these organisms are taking advantage of both the nitrogenous and organic compounds in urine for growth. The intrinsic nature of such metabolic activity in the cave environment was confirmed by examining non-impacted sites using cultivation, which demonstrated that endemic species express both the capacity to degrade urine and to reduce urea to nitrogen gas. Our results differ from those of previous studies by implying a more resilient nature of the microbial ecosystem in caves to invasion by exogenous (commensal) species, while suggesting that endemic microbial species may be able to mitigate the impact of excess nitrogen in the cave through bioremediation.

Sustained Anthropogenic Impact in Carter Saltpeter Cave, Carter County, Tennessee and the Potential Effects on Manganese Cycling

“…Localized variations in geochemistry and nutrient availability have been shown to impact microbial community structure (Johnston et al, 2012;Barton and Jurado, 2007;Shabarova and Pernthaler, 2010) and niche diversification (Engel et al, 2010;Macalady et al, 2008). Further, the composition of cave microbial communities mediates and stabilizes biogeochemical cycling and mineralization processes within an environment (Portillo and Gonzalez, 2010;Portillo et al, 2009).…”

“…represents a prominent new alternative indicator for the detection of fecal pollution in environmental samples due to an inability to survive in a non-host environment for lengthy periods of time, a strict association with warmblooded animals, and a relative abundance of members of this genus in fecal samples as compared to traditional indicators (Ahmed et al, 2008a). Molecular-based methods have also been successfully employed in other studies to detect the presence of human fecal indicators in karst aquifers (Johnson et al, 2011;Reischer et al, 2007) and human impact in caves (Johnston et al, 2012).…”

“…As a result, indirect methods of water monitoring for microbial contaminants are frequently employed by researchers: culture-based studies of water to detect coliform bacteria (Mikell et al, 1996;Rusterholtz and Mallory, 1994), molecular techniques to identify the presence/absence of fecal indicators and endemic species in karst systems (Ahmed et al, 2008;Johnson et al, 2011;Johnston et al, 2012;Porter, 2007;Roslev and Bukh, 2011), and the use of fluorescent dyetracers and microspheres to model water flow and pathogen dispersal in conduit systems (Goeppert and Goldscheider, 2011). Direct study of karst environments is restricted to open conduits that are large enough to allow for human movement and environmental manipulation.…”

Assessment of Forward Osmosis as a Possible Mitigation Strategy for Urine Management During Extended Cave Exploration

“…Many unique microbial species have been described from Lechuguilla Cave, (e.g., Cunningham et al, 1995;Johnston et al, 2012), and alterations to microbial communities have been attributed to human activities (e.g., Northup et al, 1997;Hunter et al, 2004;Johnston et al, 2012). Thus, depositing urine in the cave may result in substantial ecological impacts in urine dump sites, and in areas that are hydrologically connected to them.…”

“…Thus, depositing urine in the cave may result in substantial ecological impacts in urine dump sites, and in areas that are hydrologically connected to them. When urine is added to the cave ecosystem, it can cause rapid growth (blooms) of opportunistic microbe populations (Lavoie, 1995), which have been reported to be primarily endemic cave species that utilize both nitrogen and organic carbon from the urine (Johnston et al, 2012).…”