Metabolic Functional Community Diversity of Associated Bacteria during the Degradation of Phytoplankton from a Drinking Water Reservoir.

In the drinking water reservoir ecosystem, phytoplankton and bacteria play important roles in shaping freshwater health and function. In this work, the associated bacterial community functional diversity during degradation of phytoplankton was determined using the substrate utilization profiling (BIOLOG) technique, meanwhile, the composition and concentration of phytoplankton were examined using a microscope. The results indicated that Euglena decreased 58.33% from 0 to 38 d, while the smallest degradation of Bacillariophyta was 20.19%. Average well color development (AWCD590nm) increased during the static periods from 0 to 38 d; however, the AWCD590nm of 18 and 38 d had no significant difference (p ＜ 0.05). The Simpson's index (D) was in accordance with Shannon's diversity (H) and species richness(S); it was measured to be18 > 38 > 5 > 0d. There were significant differences in the pattern and level of carbon sources used by the phytoplankton-associated bacteria. In addition, the principle component analyses (PCA) suggested that the first principle component (PC1) and the second principle component (PC2) explained 46.76% and 21.49% of the total variation for bacterial community, respectively. Redundancy analysis (RDA) revealed that cell abundance of phytoplankton was negatively correlated with the AWCD590nm, amino acids and other functional indexes. Therefore, the data suggest that there are differences in the phytoplankton-associated bacterial community functional diversity during different static stages of water samples collected from the drinking water reservoir.

[Denitrification Characteristics and Functional Genes of Denitrifying Bacteria Under Aerobic or Anaerobic Conditions].

An efficient aerobic denitrifying bacterium was isolated from the sediments of the Jin Pen Reservoir in Xi'an. The strain was identified by morphological features and 16S rDNA sequences as Pseudomonas stutzeri and named it KK99. The denitrification characteristics of the strain and the expression level of the functional genes narG, nirS, and nosZ in aerobic/anaerobic conditions were investigated. The results showed that the strain can carry out both anaerobic and aerobic denitrification and has a high efficiency of denitrification, which occurs under both aerobic and anaerobic conditions; after 24 h, the removal rates of total nitrogen (TN) were 85.08% and 89.05%, respectively. Under both the conditions, the expression levels of the functional genes nosZ and nirS are high. nosZ plays a vital role in denitrification in the aerobic pathway, nirS plays a vital role in denitrification in the anaerobic pathway, and narG expression is low under both the conditions. At the same time, simultaneous nitrification and denitrification (SND) capacity of the strain was observed when nitrate and ammonium salts were the nitrogen sources, with the total nitrogen removal rate being 76% within 24 h in aerobic conditions. The P. stutzeri KK99 strain can be used for controlling eutrophication of micro-polluted water, and the application of total nitrogen reduction engineering.

[Vertical Distribution of Fungal Community Composition and Water Quality During the Deep Reservoir Thermal Stratification].

Freshwater fungal community composition plays pivotal roles in sustaining the function and health of drinking water reservoir ecosystems. To investigate the vertical evaluative characteristics of an aquatic fungal community under conditions of stable thermal stratification, water samples were collected at 0.5, 10, 25, 40, 60 and 70 m depths of Jinpen Reservoir during thermal stratification. Fungal community composition was determined using a high-throughput DNA sequencing technique and combined with water quality parameters. The results showed that the epilimnion, metalimnion, and hypolimnion water layers were formed in Jinpen Reservoir. The temperature decreased steadily from the surface at 22.33℃ to the bottom with 7.21℃ (P<0.05). The dissolved oxygen (DO) concentration decreased significantly from the surface to the bottom (P<0.05). The conductivity and the concentration total phosphorus and iron increased significantly from the surface to the bottom (P<0.05). The high-throughput DNA sequencing revealed a total of 1247 operational taxonomic units (OTUs), which were affiliated with four phylum, 14 classes, and 39 genera, including Zygomycota, Basidiomycota, Ascomycota, and Chytridiomycota. The highest Shannon diversity and Chao 1 were 3.45 and 360 at 60 m, respectively. The Shannon diversity and Chao 1 were significantly higher in the hypolimnion than in the metalimnion (P<0.05). Rhodotorula (27.23%), Alternaria (24.28%),Cladosporium (22.98%), Alternaria (32.00%), Didymella (17.47%), and Cladosporium (28.17%) were the dominant species at 0.5 m, 10 m, 25 m, 40 m, 60 m, and 70 m, respectively. There are a number of unclassified fungi at different water depths. The heat map profile indicated significant differences in the vertical distribution of the fungal community composition in Jinpen Reservoir. A principle component analysis (PCA) indicated that water temperature, DO, TP, and conductivity had dramatic influences on the vertical distribution of the fungal community composition. The results provide new insights on the relationship between water quality and fungal community composition during reservoir thermal stratified periods.

[Denitrification Characteristics and Community Structure of Aerobic Denitrifiers from Lake and Reservoir Sediments].

The effect of aerobic denitrifying bacteria is a hot topic in the field of water environment bioremediation. Aerobic denitrifier communities, H-30, X-10, and C-30, enriched by intermittent aeration, screened with screening culture media, and treated by ultrasonic waves, could perform high denitrification performance at the higher dissolved oxygen concentration of (7.2±0.6) mg ·L-1. The total nitrogen (TN) removal rate of aerobic denitrifier communities, H-30, X-10, and C-30, reached 83.04%, 83.40%, and 82.68%, respectively. There is lower nitrite accumulation during the process of denitrification. Illumina high-throughput DNA sequencing revealed that aerobic denitrifier compositions were significantly different among the three communities. The predominant strains of aerobic denitrifier communities, H-30, X-10, and C-30, were Bacillus subtilis, Paracoccus pantotrophus, and Pseudomonas stutzeri, respectively. The proportion of P. stutzeri in aerobic denitrifier communities H-30 and X-10 was almost the same, while Pseudomonas xiamenensis was only detected in H-30. These three efficient aerobic denitrifier communities provide a bacterium source guarantee for polluted water bioremediation of lakes and reservoirs in cities.

[Water Quality and Diversity of Denitrifier Community Structure of Typical Scenic Water Bodies in Xi'an].

Six micro-polluted landscape water bodies were selected to explore the relationship between water quality and the nirS-Type denitrifier community structure and diversity with an Illumina high-throughput sequencing technique. The results of a physico-chemical analysis of the water bodies showed that the Fengqing Park (FQ) and Laodong Park (LD) water bodies were classified as inferior Ⅴ water quality, the Qujiang Park (QJ), Mutasi Park (MTS), and Xinjiyuan Park (XJY) water bodies were classified as Ⅴ water quality, and the Yongyang Park (YY) water quality was classified as Ⅳ. The TN values varied from 1.21 mg·L-1 to 6.50 mg·L-1, with the lowest value found in YY and the highest in FQ (P<0.05). TP was significantly higher in LD (0.10 mg·L-1) and significantly lower in QJ[0.02 mg·L-1 (P<0.05)]. The NH4+-N in LD was 4.44 times higher than that in QJ and FQ (P<0.01). Illumina high-throughput sequencing revealed that the denitrifier community composition was significantly different among the six water bodies, and Paracoccus sp., Pseudomonas sp., and Rubrivivax sp. were the dominant genus species. A principle component analysis (PCA) indicated that the nirS-Type denitrifier communities of XJY and MTS were mainly regulated by NH4+-N and the permanganate index, LD and FQ were significantly influenced by NO3--N, NO2--N, TN, TP, and DO, and YY was significantly influenced by pH value. Our results showed that nirS-Type denitrifier communities were regulated by different water quality indicators.