Colonization by Aerobic Bacteria in Karst: Laboratory and In Situ Experiments

Abstract

Experiments were carried out to investigate the potential for bacterial colonization of different substrates in karst aquifers and the nature of the colonizing bacteria. Laboratory batch experiments were performed using limestone and PVC as substrates, a natural bacterial isolate and a known laboratory strain (Escherichia coli [E. coli]) as inocula, and karst ground water and a synthetic formula as growth media. In parallel, fragments of limestone and granite were submerged in boreholes penetrating two karst aquifers for more than one year; the boreholes are periodically contaminated by enteric bacteria from waste water. Once a month, rock samples were removed and the colonizing bacteria quantified and identified. The batch experiments demonstrated that the natural isolate and E. coli both readily colonized limestone surfaces using karst ground water as the growth medium. In contrast, bacterial colonization of both the limestone and granite substrates, when submerged in the karst, was less intense. More than 300 bacterial strains were isolated over the period sampled, but no temporal pattern in colonization was seen as far as strain, and colonization by E. coli was notably absent, although strains of Salmonella and Citrobacter were each observed once. Samples suspended in boreholes penetrating highly fractured zones were less densely colonized than those in the borehole penetrating a less fractured zone. The results suggest that contamination of karst aquifers by enteric bacteria is unlikely to be persistent. We hypothesize that this may be a result of the high flow velocities found in karst conduits, and of predation of colonizing bacteria by autochthonous zooplankton.

Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems

“…Experimental data have demonstrated that biofilm-coated limestone can effectively adsorb the microspheres employed in the field experiment, while having a negligible influence on suspended R. eutropha concentrations. The presence of comparable biofilms along flow paths employed by tracers in the epikarst is likely (Personné et al 2004;Castegnier et al 2006), and may thus explain the contrast in R. eutropha and fluorescent microsphere tracer responses.…”

Karst pools in subsurface environments: collectors of microbial diversity or temporary residence between habitat types

“…Although large areas of the world are influenced by karst and important processes such as groundwater recourse formation depend on the karst environment (Manda and Gross, 2006; Ford and Williams, 2007), little is known about microbial community composition and heterotrophic processes in these habitats. While research on springs and boreholes can give us a first idea about the diversity and function of microbial assemblages in karst environments (Personne et al. , 2004; Pronk et al.…”

Microbial communities in karst groundwater and their potential use for biomonitoring

“…A relative predominance of finer particles, for example, suggests an allochthonous origin and is often associated with faecal indicator bacteria contamination (Pronk et al 2007). Personné et al (2004) have studied bacterial colonisation of introduced substrates in a karst aquifer and concluded that enteric bacteria from periodical contamination with waste water were unlikely to persist in the system. Rusterholtz and Mallory (1994) have further described the bacterial community from Mammoth Cave (Kentucky, USA) sediments as highly diverse with no dominant species.…”