Formation of aerobic granular sludge under adverse conditions: Low DO and high ammonia.

In this study, two adverse environments: low dissolved oxygen (DO) and high ammonia concentration, were employed to investigate the morphology, interspecies quorum sensing, extracellular polymers (EPS) characterization and microbial communities in the formation of aerobic granular sludge. Results showed that low DO could promote filamentous bacterial outgrowth. Under high ammonia concentration aerobic granular sludge (AGS) could still be cultivated, although it was looser and lighter than the control group. During the early stage of the AGS cultivation process, AI-2 activity reached a peak value in all three reactors, and ultrasonic pre-treatment was not beneficial to the release of AI-2. During AGS formation, the production of polysaccharide exhibited increases from 12.2 % to 40.3 %, 49.6 %, and 29.3 %. And PS in R2 was the highest as the result of sludge bulking. PS/PN was 1.5~8 in the three reactors. Three-dimensional EEM fuorescence spectroscopy variation indicated the change of protein in EPS, and the highest intensity of Peak T1 was obtained. The location shift of Peak T1 was not obvious, and Peaks A, C, and T2 shifted toward longer wavelengths (red shift) of 5~60 nm, or shorter wavelengths (blue shift) of 10~25 nm on the emission scale and / or excitation scale in all three reactors. This provided spectral information on the chemical structure changes. Bacteria in R3 had the highest species diversity, and all bacteria in b-Proteobacteria were identified as genus Thauera, which suggested that simultaneous nitrification and denitrification occurred in R3. The filamentous bacteria in seed sludge and R2 were species-richer. There was a low abundance of filamentous bacteria in R1 and R3, which contributed to the granule structure stability.

Occurrence and variations of five classes of antibiotic resistance genes along the Jiulong River in southeast China.

Antibiotic resistance genes (ARGs) are emerging microbial hazards threatening human health. Many factors, including urban and agricultural activities and water environment changes, can significantly impact the variations of ARGs. An investigation on the occurrence and variations of ARGs in the Jiulong River was done in this study. The water samples were collected from 16 sites ranging from the upper branch to the river mouth of the Jiulong River, in both low- and high-flow periods. Eleven ARG families were tested and quantified by real-time PCR (SYBR Green) methods, and detection assays were conducted for tetA, tetG, aacC1, strA, ermB, cmlA5, vanA, dfrA1, sulII, blaTEM-1 and blaoxa-1 genes. Results showed that nine ARG families were found, then the swine industry and urban activities, including sewage discharge, might be responsible for the high levels of concentrations and relative abundances of ARGs, and the increase of salinity might decrease the relative abundances of ARGs. In addition, some ARG abundances were significantly correlated to the concentrations of NH4+ and PO4-3, particularly in the high-flow period. The human activities were important sources for ARGs in the Jiulong River, which have already become a threat to the safety of drinking water for the nearby cities.