Microbial biomass and activity in lead-contaminated soil

Abstract

Microbial community diversity, potential microbial activity, and metal resistance were determined in three soils whose lead contents ranged from 0.00039 to 48 mmol of Pb kg of soil-1. Biomass levels were directly related to lead content. A molecular analysis of 16S rRNAs suggested that each soil contained a complex, diverse microbial community. A statistical analysis of the phospholipid fatty acids indicated that the community in the soil having the highest lead content was not related to the communities in the other soils. All of the soils contained active microbial populations that mineralized [14C]glucose. In all samples, 10 to 15% of the total culturable bacteria were Pb resistant and had MIC of Pb for growth of 100 to 150 &mgr;M.

FIG. 1

PCA of the PLFA profiles obtained for discrete soil samples taken from an industrial site (samples I1, I2, and I3), a residential site (samples R1, R2, and R3), and an agricultural field (samples A1, A2, and A3).

FIG. 2

DGGE gel of 16S ribosomal DNA PCR products (bases 338 to 518 [Escherichia coli rRNA sequence numbering]) from lead-contaminated and uncontaminated soil DNA extracts. The denaturant gradient in the gel ranged from 30 to 55%. Lane 1 contained markers; the PCR products were products of (from top to bottom) Pseudomonas putida, Acinetobacter sp. strain ADP1, Comamonas acidovorans ATCC 15668, E. coli DH5a, Alcaligenes sp. strain BR40, and Comamonas testosteroni). Lane 2, soil contaminated with polycyclic aromatic hydrocarbons (700 ppm); lanes 3 to 5, three I soil samples (48 mmol of Pb kg⁻¹); lanes 6 to 8, three R soil samples (3.9 mmol of Pb kg⁻¹); lanes 9 to 11, three A soil samples (3.9 μmol of Pb kg⁻¹).

FIG. 3

Fraction of [¹⁴C]glucose that was recovered as ¹⁴CO₂ for three soils containing different levels of lead. The bars indicate the standard errors (n = 3).