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In this paper, the performance of membrane bioreactors (MBR) and conventional activated sludge (CAS) processes at low temperature was investigated by analyzing their effluent quality and microbial viability. 454 high-throughput pyrosequencing was also applied to study the microbial community structures. The results of three systems (two MBRs: R1 with high sludge concentration, R2 with low sludge concentration, and one CAS: R3) showed that the average removal rate of NH4(+) -N was 99.7%, 99.7% and 59.7%, respectively, and the average removal rate of TN was 85.2%, 56.1% and 58.8%, respectively. R2 showed the highest specific ammonium uptake rate (SAUR), followed by R1 and R3; R1 showed the highest specific nitrate uptake rate (SNUR), followed by R2 and R3. It could be concluded that MBRs with high sludge concentration had a better performance of nitrogen removal under low temperature operation. 454 high-throughput pyrosequencing analysis revealed that the microbial richness was R2 > R3 > R1, and the microbial diversity was R2 > R1 > R3 at 97% sequence identity. The microbial structure and bacterial abundance were quite different between MBR and CAS systems. The dominant nitrifier in this research was Nitrospira, and the total relative abundance of nitrifiers in R1, R2, R3 was 1.22%, 1.64% and 0.15%, respectively. The Zoogloea, Thauera, Comamonadaceae and Comamonas might be the dominant denitrifers in this study, and the total relative abundance of denitrifier in R1, R2, and R3 was 5.8%, 4.52% and 15.21% respectively. MBR's characteristics of long solid retention time, high sludge concentration and low total nitrogen loading well supported the accumulation of nitrifiers and denitrifiers, and improved the performance of biological nitrogen removal at low temperature.

Simultaneous nitrification and denitrification (SND) effect and phosphor removal were investigated in a one-staged aerobic submerged membrane bioreactor on pilot-scale with mixed liquor suspended solids (MLSS) 19-20 g/L. The effects of DO concentration, sludge floc size distribution on SND were studied. Test results suggested that SND was successfully performed in the membrane bioreactor (MBR) and about 70% total nitrogen removal efficiency was achieved when DO concentration was set to 0.2-0.3 mg/L. The main mechanisms governing SND were the suitable sludge floc size and the low DO concentration which was caused by low oxygen transfer rate with such a high MLSS concentration in the MBR. In the meantime, phosphor removal was also studied with polymer ferric sulfate (PFS) addition and 14 mg/L dosage of PFS was proper for the MBR to remove phosphor. PFS addition also benefited the MBR operation owing to its reduction of extracellular polymer substances (EPS) of mixed liquor.

Bacterial blight, which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating rice diseases worldwide. The development and use of disease-resistant cultivars have been the most effective strategy to control bacterial blight. Identifying the genes mediating bacterial blight resistance is a prerequisite for breeding cultivars with broad-spectrum and durable resistance. We herein describe a genome-wide association study involving 172 diverse Oryza sativa ssp. indica accessions to identify loci influencing the resistance to representative strains of six Xoo races. Twelve resistance loci containing 121 significantly associated signals were identified using 317,894 single nucleotide polymorphisms, which explained 13.3–59.9% of the variability in lesion length caused by Xoo races P1, P6, and P9a. Two hotspot regions (L11 and L12) were located within or nearby two cloned R genes (xa25 and Xa26) and one fine-mapped R gene (Xa4). Our results confirmed the relatively high resolution of genome-wide association studies. Moreover, we detected novel significant associations on chromosomes 2, 3, and 6–10. Haplotype analyses of xa25, the Xa26 paralog (MRKc; LOC_Os11g47290), and a Xa4 candidate gene (LOC_11g46870) revealed differences in bacterial blight resistance among indica subgroups. These differences were responsible for the observed variations in lesion lengths resulting from infections by Xoo races P1 and P9a. Our findings may be relevant for future studies involving bacterial blight resistance gene cloning, and provide insights into the genetic basis for bacterial blight resistance in indica rice, which may be useful for knowledge-based crop improvement. [ABSTRACT FROM AUTHOR]