Contrasts between subsurface microbial communities and their metabolic adaptation to polycyclic aromatic hydrocarbons at a forested and an urban coal-tar disposal site

Abstract

The abundance and distribution of microorganisms and their potential for mineralizing polycyclic aromatic hydrocarbons (PAHs) were measured in subsurface sediment samples at two geographically separate buried coal-tar sites. At a relatively undisturbed forested site in the northeastern United States, metabolic adaptation to the PAHs was evident: Radiolabeled naphthalene and phenanthrene were converted to (14)CO2 in core material from inside but not outside a plume of groundwater contamination. However, at the urban site in the midwestern United States these PAHs were mineralized in sediments from both contaminated and uncontaminated boreholes. Thus, clear qualitative evidence showing an adaptational response by the subsurface microbial community was not obtained at the urban site. Instead, subtler clues suggesting metabolic adaptation by subsurface microorganisms from the urban site were discerned by comparing lag periods and extents of (14)CO2 production from radiolabeled PAHs added to samples from contaminated and uncontaminated boreholes. Despite slightly higher PAH mineralization activity in contaminated borehole samples, p-hydroxybenzoate was mineralized equally in all samples from the urban site regardless of location. No striking trends in the abundances of actinomycetes, fungi, and either viable or total bacteria were encountered. However, colonies of the soil bacterium, Bacillus mycoides, were detected on enumeration plates of several samples from unsaturated and saturated zones in both urban boreholes. Furthermore, other common soil bacteria, Myxococcus xanthus and Chromobacterium violaceum, were identified in samples from the uncontaminated urban borehole. The occurrence of bacteria usually restricted to surface soil, combined with the observation of fragments of building materials in many of the core samples, suggested that past excavation and backfilling operations may have caused mixing of surface soil with subsurface materials at the urban site. We speculate that this mixing, as well as non-coal-tar-derived sources of PAHs, contributed to the PAH-mineralizing activity present in the sediment samples from the uncontaminated urban borehole.

Natural Selection of PAH-Degrading Bacterial Guilds at Coal-Tar Disposal Sites

“…As expected, the source area was most affected. The new activity and microbial distribution patterns resembled those previously seen at Site 97, where mixing of surface soil with subsurface sediment was suspected based on the occurrence of high numbers of typical soil microorganisms (e.g., endospore-forming bacteria) (7). Within the plume, the downgradient borehole (Figures 1,3) changed the least.…”

“…The 14C-mineralization results [ Figure 1, from (5), and Figure 2, from (7) than those of many surface soils (5). Bacterial numbers were also elevated in these samples, but bacterial biomass estimates alone were not a good indicator of high activity zones.…”

“…This required considerable planning and coordination of field operations to assure that equivalent samples or the same samples could be analyzed for microbial abundance [total bacteria, heterotrophic colony-forming units (CFU), protozoa, numbers] and activity (14C-naphthalene, 14C-phenanthrene, '4C-parahydroxybenzoate mineralization), as well as PAH concentration. Details of our sampling and analytical methods and procedures have been described previously (5,7). Recently, we have also employed the polymerase chain reaction and other molecular techniques in studies of the distribution of indigenous bacterial genes at Site 24 (6,10).…”

Trace metal mobilization in soil by bacterial polymers.

“…Transport of an extracellular pt aquifer sand. The polymer was produce terium isolated from subsurface soil at a cc disposal site (52).…”

Mass transfer effects on microbial uptake of naphthalene from complex NAPLs

“…Bioremediation is a favored technology for clean-up of PAH contamination. Indigenous microorganisms in contaminated aquifers are known to evolve remarkable pollutant degrading capabilities (Heidcamp and Cerniglia, 1988;Madsen et al, 1992;Cerniglia, 1992). Microorganisms that can use specific PAHs as sole sources of carbon and energy have been isolated from contaminated soil and water samples (Heitkamp and Cerniglia, 1988;Mueller et al, 1989), and the ability of these microorganisms to cometabolize several different PAHs is well documented (Mueller et al, 1989).…”