Document Type

Thesis - University Access Only

Award Date

2008

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

Abstract

Antibiotics administered for human health and to swine for growth promotion and herd health persist in treated biosolids and manure. Land spreading biosolids and manure may result in soil microbial community diversity and herbicide degrading activity changes. We hypothesized that chlortetracycline (CTC) in swine manure or tetracycline (TET) in biosolids would cause shifts in the soil microbial community and its ability to degrade the herbicide 2,4-dichlorophenoxyacetic acid (2,4-0). Field studies used a randomized plot design (n=4) conducted during summer and fall 2006. The summer season was hot and dry and the fall was cool and wet. Manure from swine fed untreated or CTC containing feed and dried biosolids or dried biosolids spiked with TET were applied to soil at about 7,000 kg/ha. Manure containing CTC contained approximately 42 mg antibiotic/32 g manure solids prior to being land spread. Dried biosolids (82 g) were spiked with 108 mg TET/10 ml water and 32g of the spiked biosolids was then land applied. 2,4-0 was applied at a rate of 2.2kg/ha to half the treatments in summer and fall 2006. Soil samples were taken 1, 7, 28, and 42 days after treatment (DAT). The aerobic culturable counts were determined using R2A agar, whereas 2,4-D degraders were determined by most probable number (MPN) technique with 2,4-D as the sole carbon and energy source. The V3 region of the 16S rRNA gene pool was amplified by polymerase chain reaction (PCR) and amplicons resolved by denaturing gradient gel electrophoresis (DOGE). Bands of interest were cloned and their sequences determined for classification purposes. Principal component analysis (PCA) was performed on DOGE banding patterns to compare microbial community shifts among treatments. The overall number of aerobic microbes, determined by culturable counts, increased (p=0.05) by the addition of manure but not manure containing CTC. 2,4-D was degraded rapidly in untreated soil with about 10% left after 7d, however, about 30% remained in the soil treated with manure+ CTC. Numbers of 2,4-D degraders increased in all treatments. DOGE analysis confirmed community shifts in response to 2,4-D within 1 DAT. Additions of either manure type also caused shifts in community structure due to the introduction of manure bacterial flora. The effect of biosolids containing TET on soil microbial communities was less pronounced than that of manure containing CTC. During the summer experiments, biosolids containing TET in the presence of 2,4-D showed unique community progressions over time, however, the final community composition at d42 was similar to soil+2,4-D. Although the fall bacterial community showed different bacterial community progression patterns for biosolids containing TET treatment, 42 DAT results were similar to that of the summer findings. Overall, manure containing CTC did have a profound effect on the soil microbial community composition over time and biosolids containing TET had a less pronounced effect. Over time, community structure shifted in all treatments, due in part to changes in soil water and temperature, but manure containing CTC treatment had the most distinctly different community compared with all other treatments. The effects of biosolids containing TET were less pronounced than the CTC findings. These results support the hypothesis that CTC in swine manure and TET in biosolids would shift the soil microbial community, ultimately effecting 2,4-D degradation.

Library of Congress Subject Headings

Antibiotics in animal nutrition -- Environmental aspects

Antibiotics in agriculture -- Environmental aspects

Swine -- Manure

Sewage sludge

Soil microbial ecology -- South Dakota

Tetracycline

Format

application/pdf

Number of Pages

196

Publisher

South Dakota State University

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