The spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) has become an increasingly serious global public health issue. This study investigated the distribution characteristics and influencing factors of ARB and ARGs in greenhouse vegetable soils with long-term application of manure. Five typical ARGs, four heavy metal resistance genes (MRGs), and two mobile genetic elements (MGEs) were quantified by real-time quantitative polymerase chain reaction (qPCR). The amount of ARB in manure-improved soil greatly exceeded that in control soil, and the bacterial resistance rate decreased significantly with increases in antibiotic concentrations. In addition, the resistance rate of ARB to enrofloxacin (ENR) was lower than that of tylosin (TYL). Real-time qPCR results showed that long-term application of manure enhanced the relative abundance of ARGs in vegetable soils, and the content and proportion of quinolone resistance genes were higher than those of macrolide resistance genes. Redundancy analysis (RDA) showed that qepA and qnrS significantly correlated with total and available amounts of Cu and Zn, highlighting that certain heavy metals can influence persistence of ARGs. Integrase gene intI1 correlated significantly with the relative abundance of qepA, qnrS, and ermF, suggesting that intI1 played an important role in the horizontal transfer of ARGs. Furthermore, there was a weakly but not significantly positive correlation between specific detected MRGs and ARGs and MGEs. The results of this study enhance understanding the potential for increasing ARGs in manure-applied soil, assessing ecological risk and reducing the spread of ARGs.
Benzotriazole (BTA) is an emerging contaminant that also is a recalcitrant compound. Sequential and intimate coupling of UV-photolysis with biodegradation were investigated for their impacts on BTA removal and mineralization in aerobic batch experiments. Special attention was given to the role of its main photolytic products, which were aminophenol (AP), formic acid (FA), maleic acid (MA), and phenazine (PHZ). Experiments with sequential coupling showed that BTA biodegradation was accelerated by photolytic pretreatment up to 9 min, but BTA biodegradation was slowed with longer photolysis. FA and MA accelerated BTA biodegradation by being labile electron-donor substrates, but AP and PHZ slowed the rate because of inhibition due to their competition for intracellular electron donor. Because more AP and PHZ accumulated with increasing photolysis time, their inhibitory effects began to dominate with longer photolysis time. Intimately coupling photolysis with biodegradation relieved the inhibition effect, because AP and PHZ were quickly biodegraded and did not accumulate, which accentuated the beneficial effect of FA and MA.
The production of commercial livestock and poultry often involves using with antibiotics and feed additives, such as oxytetracycline (OTC) and copper (Cu). These are often excreted into the soil by animal feces; hence, combined pollutants may contaminate the soil. To evaluate single and combined toxic effects of OTC and Cu on the soil ecology, changes in quantities of bacteria, fungi, and actinomycetes in the soil were studied over a 28-d incubation period by a plate count method, microbes numbers counted on days 7, 14, 21, and 28. Abundances of ammonia monooxygenase (amoA) gene expression by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in soil samples also were tested by real-time polymerase chain reactions (RT-PCRs) on day 21. The results revealed that the numbers of bacteria, fungi and actinomycetes and amoA genes copies of AOA and AOB were reduced seriously by exposure to Cu (1.60 mmol/kg). Similarly, the combined pollution treatments (mole ratios of OTC: Cu was 1:2, 1:8, and 1:32) also had inhibitory effect on bacteria, fungi, and actinomycetes numbers and amoA gene copies of AOA and AOB; the inhibitory rate was on obvious growth trend with the increasing mole ratios. Effects from single OTC pollution were found on bacteria (days 7 and 14), fungi (days 7, 14, 21, and 28), and AOA-amoA gene copies (day 21), with promotion at a low concentration (0.05 mmol/kg) and suppression at higher concentrations (0.2 and 0.8 mmol/kg). Also, numbers of bacteria, fungi, and actinomycetes decreased with longer culture times. Combining OTC and Cu led to a higher inhibition of soil microbes than when either chemical was used alone. However, there was no significant relationship between single and combined toxic chemicals because of their complicated interactions, either antagonistic or synergistic. The results also indicated the sensitivity of bacteria, fungi, actinomycetes on toxic chemicals existed difference and that the AOA were more tolerant than the AOB to these chemicals. 相似文献