Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2005
Publication Date: 2/2/2006
Citation: Becer, J.M., Parkin, T.B., Nakastu, C.H., Wilbur, J., Konopka, A. 2006. Bacterial activity, community structure, and degree of spatial hererogeneity on the small scale at a long-term contaminated site. Microbial Ecology. 51(2):220-231.
Interpretive Summary: Soil bacteria carry out many important functions, including: the recycling of plant nutrients, production and consumption of greenhouse gases, and the breakdown of pollutants. Because bacteria are so small it is difficult to determine how they carry out many of these important functions. This study combined the use of genetic techniques with statistical procedures to study the spatial distribution of bacteria in a soil that had a history of contamination with heavy metals and organic pollutants. With the combination of these two techniques we were able to determine that bacteria in soil were influenced by how the pollution was distributed in soil. Distinct pockets of bacteria were identified, and in some of these pockets, the bacteria had adapted to the harsh conditions imposed by the pollutants. This information will be useful to scientists studying the ecology of soil bacteria.
Technical Abstract: In an anthropogenically disturbed soil, (88% sand, 8% silt, 4% clay) 150 mg samples were studied to examine the fine scale relationship of bacterial activity and community structure to heavy metal contaminants. The soils had been contaminated for over 40 years with aromatic solvents, lead (Pb), and chromium (Cr). Samples from distances of <1, 5, 15, and 50cm over a depth range of 40 to 90 cm depth underwent a sequential analysis to determine metabolic activity (from 14C-glucose mineralization), bacterial community structure (using PCR-DGGE), and total extractable Pb and Cr levels. Metabolic activity varied by as much as 10,000-fold in samples <1cm apart; log-log plots of metal concentration and microbial activity showed no correlation with each other. Overall, metal concentrations ranged from 9-29,000 mg kg-1 for Pb and 3-8500 mg kg-1 for Cr with small zones of high contamination present. All regions exhibited variable metal concentrations, with some soil samples having 30-fold differences in metal concentration in sites <1cm apart. Geostatistical analysis revealed a strong spatial dependence for all 3 parameters tested (metabolic activity, Pb, and Cr levels) with a range up to 30 cm. Kriging showed that in zones of high metal, the corresponding metabolic activity was low suggesting that metals negatively impacted the microbial community. PCR-DGGE analysis revealed that diverse communities were present in the soils with a random distribution of phylotypes throughout the sampling zones. These results suggest the presence of spatially isolated microbial communities within the soil profile.