Influence of Agricultural Antibiotics and 17β-Estradiol on the Microbial Community of Soil

Agricultural pharmaceuticals are a major environmental concern because of their hazardous effects on human and wildlife. This study analyzed phospholipid ester-linked fatty acids (PLFAs) and quinones to investigate the effects of a steroid (17β-estradiol) and agricultural antibiotics (chlortetracycline and tylosin) on soil microbes in the laboratory. Two different types of soil were used: Sequatchie loam (0.8% organic matter) and LaDelle silt loam (9.2% organic matter). The soils were spiked with 17β-estradiol and antibiotics, alone or in combination. In Sequatchie loam, 17β-estradiol significantly increased the microbial biomass, especially the biomarkers for beta proteobacteria (16:1ω7c, 18:1ω7c, Cy17:0, and UQ-8). The coexistence of antibiotics decreased the stimulatory effect of 17β-estradiol on the microbial community. In LaDelle silt loam, there were no significant differences in total microbial biomass and their microbial community structure among the treatments. Overall, 17β-estradiol changed the microbial community of soil and the presence of antibiotics nullified the effect of 17β-estradiol. However, the effects of 17β-estradiol and antibiotics on soil microbes were sensitive to the soil properties, as seen in the LaDelle silt loam.

Key Words:

• Microbial community
• Phospholipid ester-linked fatty acids (PLFAs)
• Quinones
• 17β-estradiol
• Agricultural antibiotics

ACKNOWLEDGMENTS

This work was supported by the Korea Research Foundation Grant funded by the Korean Government (KRF-2005-217-F00002). We would like to thank Margaret Gan, Amanda N. Smithgall, and James M. Cantu at the Center for Biomarker Analysis, University of Tennessee, for a technical assistance of PLFA analysis.

Notes

^†)∗, ∗∗, and ∗∗∗ are significant at the 0.05, 001, and 0.001 levels, respectively.

^‡) br, a branched fatty acid; i, iso methyl branching fatty acid; a, anti-iso methyl branching fatty acid; Cy, cyclopropyl isomer of a fatty acid; c, cis isomers of a fatty acid; number preceding the abbreviation Me, the position of a methyl group relative to the carbonyl carbon.

^§)Within the same row, values with the same letter are not significantly different at the 0.05 probability level by the Tukey's Honest Significant Difference test.