Impacts of Ciprofloxacin on Plant Growth and Soil Microbial Biomass

Abstract

Antibiotics are finding their way into different compartments of environment and causing damage to non-target organisms. In present study, the effects of ciprofloxacin (CIP) stress at various concentrations on plant growth and soil microbial biomass were investigated. For plant growth test, pot experiment was performed with CIP as an amendment and the effect was evaluated by harvesting the plants after 28 days of sowing and measuring their lengths and biomass. Soil microbial biomass, organic matter and microbial growth were determined using chloroformfumigation extraction (CFE), Walkey-Black procedure and optical density measurements, respectively. In CFE, the increase in extractable microbial carbon following fumigation of soil with chloroform is determined. For Walkley-Black chromic acid wet oxidation method, organic matter in the soil is oxidised by chromic acid solution. To test microbial growth, change in optical density was measured using spectrophotometer to determine the concentration of bacteria in suspension. The results showed that CIP impacted shoot length significantly only at the highest concentration of 200 mg L-1 whereas no effect was observed on root length. The fresh biomass of roots suffered a decline of 9.6 and 8.9% at 100 and 200 mg L-1 while the decline of 35 and 44.5% was observed for fresh shoot biomass. The negative impacts of CIP were much more prominent in case of soil microbial biomass. Using chloroform-fumigation extraction, the decline observed in the microbial biomass after 15 day’s incubation period was 0.089, 7.96, 21.1, 30.9 and 48.1% at 50 (C1), 75 (C2), 100 (C3), 150 (C4) and 200 mg L-1 (C5), respectively. Organic matter also observed a declining trend with increase in CIP concentrations from C1 to C3 after which it stabilized. The soil microbial population in terms of optical density over 3 days, exposure showed an increased potency of the drug at high concentrations. Zone of inhibition test reaffirmed inhibitory effects of CIP. The zone increased from 12.6 to 24.9 cm at CIP concentrations from 2.5- 200 mg L-1 for E. coli. While for P. aeruginosa, the inhibition zone observed was from 11.5 to 28 starting from CIP concentration of 5 mg L-1