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Effects of Veterinary Medicines on the Structural Diversity of the Microbial Biomass in Soils.

Prof. Dr. Thiele-Bruhn, Universität Trier

Summary

Veterinary antibiotics reach agricultural soil together with manure as a complex, microbially populated, nutrient-rich substrate. Impacts on the soil microbial community and its structural diversity, functions and resistance level are expected. Hence our central hypothesis in all phases of within FOR566 was that antibiotic pharmaceuticals exert adverse effects on soil microorganisms, reflected in shifts in their structural diversity. This was investigated with samples from microcosm, pot (greenhouse), mesocosm, and field experiments by using PLFA analysis and fingerprints from DGGE separated 16S rRNA genes, in part complemented by subsequent sequencing and FISH analysis. Significant effects of the investigated antibiotics on the microbial community structure were determined in experiments on all spatial scales. Overall, the presence of antibiotics in manure caused shifts from bacteria to fungi and in parts shifts between gram+ and gram bacteria within the bacterial community, with Pseudomonas being particularly sensitive. This corresponds to findings of project B2, which also demonstrated shifts from bacteria to archaea after exposure to SDZ-containing manure. Community shifts were often, but not necessarily, accompanied by effects on microbial functions, emphasizing the functional redundancy within soil microbial communities. An increase in the resistance level shown by project B3 clearly documented that community shifts go along with a selection of tolerant and/or antibiotic resistant species. Effects on the community structure evolved a few days after adding antibiotics to soil and further increased and persisted over a long-term of 252 days and possibly beyond. These dynamics did not follow the rapid decline in the bioavailable fraction of the antibiotics, thus leading to an apparent concentration independence of the effects. Furthermore, effects interacted with manure composition and varied with the applied amount of manure. This was because manure acted as substrate and microbial inoculum, whose molecular and microbial composition is already changed within the digestive tract of medicated organisms. Furthermore, parent compounds and metabolites might be transformed during manure storage. Hence, a mixed effect of manure composition, manure-derived microorganisms that survive in soil for several weeks, transformation products of the antibiotic, and the antibiotic itself on soil microorganisms must be expected when soils are fertilized with manure that contains antibiotics. However, storage of manure was not suited to mitigate effects of sulfonamides in soil since SDZ reacted back from the acetyl conjugate to the parent compound. Manure constituents and antibiotics accumulated in outer shells of soil macroaggregates and earthworm burrows. In the latter, significant shifts in the microbial community structure were even significant after 252 days of a field experiment. In contrast, the rhizosphere is a microcompartment of higher resilience, able to mitigate antibiotic effects on the microbial community, which is reflected by a stronger dissipation and transformation of SDZ. Yet, strong effects on plants were identified even at SDZ concentrations that were close to what can be expected in the field. This included hormone-like effects on root geotropism and ramification, and affected plant water and nutrient uptake. Furthermore, antibiotic effects on microbial communities were more pronounced in soils exposed to periodic changes in soil moisture by drying-rewetting dynamics. Drying and rewetting increased the potentially bioaccessible SDZ concentrations. The combined stress from SDZ and strong moisture dynamics lowered the microbial biomass, which trend was also determined under complex field conditions. The studies clearly document the environmental relevance of pharmaceutical antibiotics reaching agricultural soils.

 

begutachtete Publikationen:

  1. Hammesfahr U, Thiele-Bruhn S, Manzke B, Heuer H, Smalla K (2008): Effect of sulfadiazine and pig slurry on the structural diversity of soil microorganisms, Soil Biology and Biochemistry 40, 1583–1591.
  2. Hammesfahr U, Bierl R, Thiele-Bruhn S (2011a): Manure and the antibiotic sulfadiazine are interacting on microbial biomass and structure. Journal of Plant Nutrition and Soil Science 174, 614–623.
  3. Hammesfahr U, Kotzerke A, Lamshöft M, Wilke BM, Kandeler E, Thiele-Bruhn S (2011b): Sulfadiazine contaminated fresh and stored manure modifies the function and structure of soil microbial community. European Journal of Soil Biology 47, 61–68.
  4. Michelini L, Reichel R, Werner W, Ghisi R, Thiele-Bruhn S (2012): Sulfadiazine uptake and effects on Salix fragilis L. and Zea maize L. plants. Water, Air and Soil Pollution 223, 5243–5257.
  5. Reichel R, Rosendahl I, Peeters ETHM, Focks A, Groeneweg J, Bierl R, Schlichting A, Amelung W, Thiele-Bruhn S (2013): Effects of slurry from sulfadiazine- (SDZ) and difloxacin- (DIF) medicated pigs on the structural diversity of microorganisms in rhizosphere soil. Soil Biology and Biochemistry 62, 82–91.
  6. Reichel, R, Patzelt, D, Barleben, C, Rosendahl, I, Ellerbrock, RH, Thiele-Bruhn, S (2014a): Microbial community structure and function of diverse soil microhabitats respond differently to sulfadiazine antibiotic co-applied with pig manure. Applied Soil Ecology 80, 15-25.
  7. Reichel, R., Viviane Radl, Ingrid Rosendahl, Andreas Albert, Wulf Amelung, Michael Schloter, Sören Thiele-Bruhn (2014b): Soil microbial community responses to antibiotic-contaminated manure under different soil moisture regimes. Applied Microbiology and Biotechnology 98, 6487-6495.

 

Weitere Publikationen:

  1. Hammesfahr, U. (2011): Alterations in soil microbial structure and function due to different manure and antibiotic loads. PhD thesis, Trierer Bodenkundliche Schriften 16, 98 pp.
  2. Thiele-Bruhn, S., Aust, M.-O. (2013) Stoffdatenblatt: Sulfonamide. In: Litz, N., Wilcke, W., Wilke, B.-M. (Hrsg.) Bodengefährdende Stoffe. Kap. VI-2, 1-64. ecomed Verlagsgesellschaft, Landsberg/Lech.
  3. Reichel, R. (2014): Soil microbial community responses to antibiotic pharmaceuticals: influence of different soil habitats and moisture regimes. Dissertation. University of Trier, 208 pp.

 

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