Abstract
Despite many studies, our knowledge on the impact of antibiotics and antibiotic-resistant bacteria on the metabolic activity of soil microbial communities is still limited. To ascertain this impact, the community level physiological profiles (CLPPs) and the activity of selected enzymes (dehydrogenase, urease, and phosphatases) in soils treated with vancomycin (VA) and/or multidrug resistant Citrobacter freundii were determined during a 90-day experiment. A multivariate analysis and the resistance (RS)/resilience (RL) concept were used to assess the potential of native microorganisms to maintain their catabolic activity under exposure of VA and/or a high level of C. freundii. In addition, the dissipation rate of VA was evaluated in non-sterile (nsS) and sterile (sS) soils. The results revealed a negative impact of VA on the metabolic activity of soil microorganisms on days 1, 15, and 30 as was showed by a decrease in the values of the CLPP indices (10–69%) and the enzyme activities (6–32%) for treated soils as compared to the control. These observations suggested a low initial resistance of soil microorganisms to VA and/or C. freundii but they were resilient in the long term. Considering the mean values of the RS index, the resistance of measured parameters was categorized in the following order: alkaline phosphatase (0.919) > acid phosphatase (0.899) > dehydrogenase (0.853) > the evenness index (0.840) > urease (0.833) > the Shannon-Wiener index (0.735) > substrate richness (0.485) > the AWCD (0.301). The dissipation process of VA was relatively fast and independent of the concentration used. The DT50 values for VA applied at both concentrations were about 16 days. In addition, the dissipation of VA in nsS was three times faster compared to the dissipation of antibiotic in sS. In conclusion, both CLPP and enzyme activities assays appeared to be useful tool for the determination of disturbances within soil microbial communities and used together may be helpful to understand the changes in their catabolic features. The entry of large quantities of VA and/or C. freundii into soil may temporarily change microbial activity thus pose a potential risk for soil functioning.
Highlights
Antibiotics and antibiotic-resistant microorganisms are primarily introduced into soil through the manure, municipal wastewater, or sewage sludge application (Kümmerer, 2003; Chee-Sanford et al, 2009; Li and Zhang, 2010)
We observed a decrease in the metabolic activity of soil microorganism as was indicated by the data from community level physiological profiles (CLPPs) and enzyme activities
On the sampling days, no effects or stimulation of microbial activity were found. These results suggest that as long as VA was present in the soil, it negatively affected microbial activity
Summary
Antibiotics and antibiotic-resistant microorganisms are primarily introduced into soil through the manure, municipal wastewater, or sewage sludge application (Kümmerer, 2003; Chee-Sanford et al, 2009; Li and Zhang, 2010). Several antibiotics are used and overused in agriculture practices (Chang and Ren, 2015). Due to their potential ecotoxicological effects and persistence in soil, antibiotics represent a durable contamination (Brandt et al, 2015). Many studies have revealed that antibiotics affect the number of different groups of microorganisms (Pinna et al, 2012; Akimenko et al, 2015; Xu et al, 2016), the structural and genetic diversity of microorganisms and the overall microbial activity (Demoling et al, 2009; Cui et al, 2013; Liu et al, 2014; Reichel et al, 2014a,b; Cyconet al., 2016a; Xu et al, 2016). The impact of antibiotics on the enzyme activities, carbon mineralization, and nitrogen cycling has been proven (Liu et al, 2009; Kotzerke et al, 2011; Rosendahl et al, 2012; Chen et al, 2013; Ma et al, 2016)
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