The impact of antibiotics on denitrification has attracted widespread attention recently. Norfloxacin, as a representative of fluoroquinolone antibiotics, is extensively detected in groundwater. However, whether the release of norfloxacin into the groundwater poses potential risks to denitrification remains unclear. In this study, effect of norfloxacin on denitrification was investigated. The results showed that increasing norfloxacin from 0 to 100 μg/L decreased nitrate removal rate from 0.68 to 0.44 mg/L/h, but enhanced N₂O emission by 177 folds. Additionally, 100 μg/L of norfloxacin decreased nitrite accumulation by 50.6%. Corresponding inhibition of norfloxacin on bacterial growth, carbon source utilization, electron transport system activity and genes expression was revealed. Furthermore, denitrifying enzyme dynamic monitoring results showed that norfloxacin inhibited nitrate reductase activity, and enhanced nitrite reductase activity to some extent in denitrification process, which was consistent with the variations of nitrate and nitrite. Meanwhile, sensitivity analysis demonstrated that nitrate reductase was more easily affected by norfloxacin than nitrite reductase. Overall, this study suggests that multiple regulation of denitrifying enzyme activity contributes to evaluating the comprehensive effects of antibiotics on groundwater denitrification.

Mangrove has been destroyed and reforestation is often undertaken, but whether a regenerated forest could restore its ecological function is not clear. This study compares microbial community structure and function in sediment of the 17-years old natural regenerated mangrove forest (Y17) with the original forest (Y74). No significant differences in phospholipid fatty acid (PLFA) profiles and microbial metabolism of most carbon substrates were found between these two forests. However, activities of dehydrogenase, protease, cellulase and phosphatase were lower in Y17 than Y74, and some specific microbial functions were also different. Both forests exhibited significant seasonal differences in enzyme activities and microbial characteristics, but such difference was larger in Y17 than Y74, indicating the regenerated forest was more sensitive to season. Correspondence analysis based on PLFA profiles and enzyme activities revealed the microbial community in Y17 was comparable to Y74, suggesting sediment microbial characteristics in natural regenerated mangroves could be restored.

The present study examined the relationships between soil characteristics, microbial community structure and function in the forests artificially planted with exotic Sonneratia apetala at stand ages of 1-, 2-, 7-, 10- and 14-years and Sonneratia caseolaris of 1-, 4-, 7-, 10- and 14-years in Futian National Nature Reserve, Shenzhen Bay, China. The 7-years old forests of both Sonneratia species reached peak growth and had the highest content of nitrogen and phosphorus, enzymatic activities, including dehydrogenase, cellulase, phosphatase, urease and ß-glucosidase, except arylsulphatase which increased continuously with stand ages. The microbial community structure reflected by phospholipid fatty acid (PLFA) profiles also reached the maximum value in the 7-years old forests and soil bacterial PLFAs in both forests were significantly higher than fungal PLFAs. The canonical correlation analysis revealed that differences in microbial structural variables were significantly correlated to the differences in their functional variables, and the highest correlation was found between the soil enzymatic activities and the content of carbon and nitrogen.

The marine plastic pollution has drastic effect on marine species. The importance in environmental issues increases the demand to develop a significant technology which does not burden the marine environment or marine life forms. To mitigate the foreseen problems of micro and nanoplastic contamination, different biotechnological solutions has to be considered. Microbial communities exposed to plastic contaminated sites can adapt and form dense biofilms on the plastic surface and produce active catalytic enzymes. These enzymes can be able to degrade the synthetic polymers. In view of their high catalytic activity, microbial enzymes can be applicable for the degradation of synthetic polymers. This review highlights the toxicity of micro and nanoplastics on marine organisms, biodegradation of plastics and futuristic research needs to solve the issues of plastic pollution in marine environment.