Single And Joint Toxicity Of Enrofloxacin And Cd On Soil Microbial Community Structure And Function

With the development of the aquaculture industry in recent years, antibiotics are widely used and cannot be completely decomposed in the body of a livestock, entered into the soil with excrements of livestocks. Excrements of livestocks contain heavy metals such as Cu, Zn and Cd, causing the joint toxicity of antibiotics and heavy metals on soil environment. The study of compound pollution between antibiotics and heavy metals helps to correctly evaluate migration and transformation rules of pollutants under compound pollution, providing important basis for evaluation of soil environmental quality. The study regarded the typical antibiotics enrofloxacin(ENR) and Cd as target contaminants, using traditional methods and means of molecular biology to study the effect of single and joint toxicity of ENR(0, 0.025,0.1, 0.4 mmol/kg) and Cd(0, 0.4 mmol/kg) at a ratio of 1:1, 1:4, 1:16 on days 7, 14, 21, 28 on soil microbial community structure and function in the lab simulation, then to evaluate the joint toxicity of ENR and Cd. The study results are summarized as follows:(1) Single and joint toxicity of ENR and Cd on the quantity of soil microorganism: by the method of the plate colony count, the experiment results showed that the quantities of soil microorganism were all decreased with the inscreasing concentration of ENR at the whole experiment period and inhibition ratio was bacteria > actinomycetes > fungi,interaction type of joint toxicity on three soil microorganism were mainly antagonism effect.(2) Single and joint toxicity of ENR and Cd on soil enzyme activity: compared with controls, the single pollution of ENR had no differences to phosphatase; high concentrations(0.4 mmol/kg ENR) had a significantly inhibitory effect on urea enzyme activity; the high concentration of ENR had a significantly inhibitory effect on sucrose enzyme in the most experiment period; high concentrations of ENR had showed promotion firstly and then inhibition effect on hydrogen peroxide enzyme; single pollution of Cd showed obvious inhibition effects on four kinds of soil enzyme. In the whole experiment, compound pollution of ENR and Cd had showed no significant promotion effects on phosphatase and catalase activities at the beginning and then showed no significant inhibition effects; compound pollution in the whole period showed a significant difference increase on urease activity with the increasing concentration of ENR; compound pollution of ENR and Cd had showed significant difference effect on the invertase activity of inhibition firstly, then of promotion and of inhibition at last; compound pollution of ENR and Cd had a interactions withantagonism effect on four types of enzyme activity in the entire cycle,.(3) Single and joint toxicity of ENR and Cd on soil microbial functional diversity: by the method of BIOLOG ECO, AWCD, three index(Shannon, Simpson, Mcintosh) and soil microbial capability of utilising the carbon source on days 14, 21 had been tested.Single and joint toxicity of ENR and Cd on AWCD of soil microorganism kept unchanged in the early time and gradually increased in later, compound pollution of high concentration ENR inhibited AWCD slightly in the whole experiment time.Single pollution of ENR had no significant difference on Shannon index compared with control group, Shannon index had no significant difference on days 14 under compound pollution, and increased on days 21; Simpson index was less than control under ENR pollution at 14 d and 21 d, showing that ENR had lead the decrease of the species richness, and the same result was at 14 d under compound pollution and 21 d under compound pollution of a high ENR concentration. And Simpson index at 21 d was greater than the control under compound pollution of low ENR concentration. Mcintosh index at 14 d and 21 d were less than control and had no significant difference under single pollution of ENR, and Mcintosh index increased under composite pollution treatments, indicating that species had a better the homogeneity.Single and joint toxicity of ENR and Cd had different effects on soil microbial capability of utilising carbon source, the utilization sequence was: lipid and fatty acid > amino acid and its derivatives > glucide and its ramifiation > metabolic intermediate and secondary metabolites. With the increasing concentrations of ENR in compound pollution, the utilization strength of carbon source gradually reduced and was lower than the control finally.(4) Single and joint toxicity of ENR and Cd on AOA and AOB: by the method of RT-PCR, the results showed that AOA-amoA gene copy number was greater than AOB,about one order of magnitude higher in the entire treatment group. Compound pollution has a higher inhibitory effect on AOB than that on AOA. When 0.025 mM/kg and 0.1mM/kg ENR contaminated soil, compared with control, at 14 d AOA-amoA gene copy number had a promotion effect, other treatments showed a significant differences in inhibitory effect,however, at 21 d, most of the treatment groups had significant differences in inhibitory effect on AOA-amoA. Each treatment group at 14 d and 21 d are characterized by significant inhibitory effect on AOB-amoA; compound pollution had a synergistic effect on AOA mainly and had an antagonism effect on AOB.