Responses of microbial community and antibiotic resistance genes to co-existence of chloramphenicol and salinity.

In recent years, the risk from environmental pollution caused by chloramphenicol (CAP) has emerged as a serious concern worldwide, especially for the co-selection of antibiotic resistance microorganisms simultaneously exposed to CAP and salts. In this study, the multistage contact oxidation reactor (MCOR) was employed for the first time to treat the CAP wastewater under the co-existence of CAP (10-80 mg/L) and salinity (0-30 g/L NaCl). The CAP removal efficiency reached 91.7% under the co-existence of 30 mg/L CAP and 10 g/L NaCl in the influent, but it fluctuated around 60% with the increase of CAP concentration and salinity. Trichococcus and Lactococcus were the major contributors to the CAP and salinity shock loads. Furthermore, the elevated CAP and salinity selection pressures inhibited the spread of CAP efflux pump genes, including cmlA, tetC, and floR, and significantly affected the composition and abundance of antibiotic resistance genes (ARGs). As the potential hosts of CAP resistance genes, Acinetobacter, Enterococcus, and unclassified_d_Bacteria developed resistance against high osmotic pressure and antibiotic environment using the efflux pump mechanism. The results also revealed that shifting of potential host bacteria significantly contributed to the change in ARGs. Overall, the co-existence of CAP and salinity promoted the enrichment of core genera Trichococcus and Lactococcus; however, they inhibited the proliferation of ARGs. KEY POINTS: • Trichococcus and Lactococcus were the core bacteria related to CAP biodegradation • Co-existence of CAP and salinity inhibited proliferation of cmlA, tetC, and floR • The microorganism resisted the CAP using the efflux pump mechanism.

[Nitrogen Removal Performance of a Sulfur/Pyrite Autotrophic Denitrification System].

In order to search for an economical, rapid, and highly efficient nitrogen removal process for sewage, a sulfur/pyrite packed column reactor was fed with low C/N municipal sewage. The effects of temperature, the sulfur-to-pyrite volume ratio, and hydraulic retention time (HRT) on nitrogen removal were studied. The results showed that with an influent total nitrogen (TN) of 40 mg·L-1, the optimal HRT of the No.1 reactor was 2.5 h, and the removal rate and effluent concentration of TN were stable at 72.2% and 10.55 mg·L-1, respectively. The optimal HRT of the No.2 reactor was 3.5 h, and the removal rate and effluent concentration of TN were stable at 67.8% and 12.90 mg·L-1, respectively. The optimal HRT of the No.3 reactor was 3.5 h, and the removal rate and effluent concentration of TN were stable at 60.6% and 15.00 mg·L-1, respectively. The sulfur/pyrite autotrophic denitrification system starts faster than the pyrite autotrophic denitrification system. Its nitrogen removal rate decreased with decreasing sulfur-to-pyrite volume ratio. The nitrogen removal performance of the system is not sensitive to temperature, and the denitrification performance is better than that of the system with pyrite alone as the sulfur source. The main functional bacteria in the system are Sulfurimonas and Thiobacillus, and the proportion of the sum of these two bacteria in the three reactors decreased from No.1 to No.3.