Antibiotic Effects On Microbial Respiration In Two Wetland Soils.

Antibiotics are regularly detected in the environment, and come from a variety of sources including agriculture or wastewater discharge.  The impact antibiotics have on bacterial respiration in the environment is relatively unknown. Ciprofloxacin, sulfamethoxazole and tetracycline were added to a mineral and peat wetland soil to examine effects on microbe facilitated evolution of methane, carbon dioxide and nitrogen gas. The antibiotics both positively and negatively affected microbial respiration rates in the two wetland soils. Sulfamethoxazole reduced CO₂ respiration rates at higher concentrations (500, 1000 ppb) initially in the mineral wetland soil.  However, the respiration rates recovered within 48 hours. Sulfamethoxazole also decreased methane and carbon dioxide respiration rates at low concentrations (1, 50, 100 ppb) in a peat soil, but not at higher concentrations (500, 1000 ppb). This phenomenon was also observed for Ciprofloxacin in both the mineral and peat soils when measuring denitrification.  The three compounds investigated also increased soil microbial respiration in a few instances. Generally respiration rates recovered after a brief period of time. At environmentally relevant aqueous concentrations (1 ppb), antibiotics have the ability to influence microbial activity. Based on the results, sorption and carbon limitation appear to affect the influence of antibiotics. Future studies examining the microbial community structure are needed to provide further insight into the antibiotic effects on microbial respiration.