[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 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.