[Structural Characteristics of Phytoplankton Communities and Its Relationship with Environmental Factors in a Group of Drinking Water Reservoirs by Water Transmission from Modaomen Waterway in Zhuhai].

Modaomen Waterway is the main outlet of the Pear River system and an important water source for Zhuhai and Macao. The water quality of 13 sampling sites in Modaomen Waterway, phytoplankton, and environmental factors were investigated at 21 sampling sites in 4 drinking water source groups, which transport water from Modaomen Waterway and connect with each other, in August and October of 2021. A total of 73 genera of phytoplankton in eight phyla were identified, with a total of 150 species, most of them belonging to Cyanophyta, Chlorophyta, and Bacillariophyta. The relative abundance of Cyanophyta was higher than 90% in the DJS and YL reservoirs during flood and dry seasons; Cyanophyta, Chlorophyta, and Bacillariophyta were dominant phyla during different seasons; and their distribution was balanced in the ZXD and ZY reservoirs. The Shannon-Wiener index, Pielous uniformity index, and Margalef richness index showed that the ZY reservoir had the most abundant biodiversity, which indicated the best water quality, followed by the ZXD and YL reservoirs. Conversely, the DJS was the least diverse reservoir for phytoplankton. The PCoA analysis indicated significant differences in plankton structures in ZXD and ZY with the other two reservoirs (P<0.05), respectively. Redundancy analysis (RDA) showed that the main environmental factors affecting the distribution of the phytoplankton community were NO3-, TOC, TP, Cl-, and NH4+-N. These results indicated that the phytoplankton community of the four reservoirs were greatly affected by the nutrient salt caused by water transport, which suggested that the water quality of Modaomen Waterway should be improved to increase reservoir water nutrition to ensure the safety of drinking water sources.

[Response of Photosynthetic Bacterial Community to Cadmium Contamination in Paddy Soil].

Heavy metal pollution in rice fields leads to huge losses in rice yield every year and is thus of increasing concern. Therefore, it is important to understand the changes in the microecology and physicochemical properties of paddy soil under different levels of cadmium pollution. The purpose of this study was to investigate the response of the photosynthetic bacterial community in paddy soil to different cadmium pollution levels using 16S sequencing technology. The results showed that pH, total cadmium, and available cadmium content decreased gradually with the increase in cadmium pollution. The soil α diversity was slightly different in the high cadmium (Cd), medium Cd, and low Cd groups; however, the enriched photosynthetic populations and photosynthetic bacterial communities were significantly different among these groups. The effective connections between photosynthetic bacterial species in the high Cd group were significantly greater than those in the medium and low Cd groups, the connections were closer, and the density was higher. Alkaline nitrogen, pH, available (P/K), total (N/P), organic matter, total cadmium, and available cadmium were important factors affecting the photosynthetic bacterial community and were significantly correlated with the photosynthetic bacterial community, explaining 59.90% of the variation in the photosynthetic bacterial community. Effective Cd content was significantly positively correlated with Methylorubrum populi, Methylorubrum extorquens, Methylobacterium sp. Leaf125, and Rhodopseudomonas sp. AAP120 (R>0.05, P<0.05). This study will provide a theoretical basis for the microbial remediation of cadmium contamination in paddy fields. This study is important for understanding the effects of cadmium pollution on specific functional microbial populations in paddy soils.

[Effects of Chromium Pollution on Soil Bacterial Community Structure and Assembly Processes].

With the rapid development of industry, chromium (Cr) has become one of the main soil heavy metal pollutants in China, seriously affecting the soil ecological environment and health of residents. In this study, contaminated soil samples were taken around the tannery sludge yard area in Heibei Province. The Illumina MiSeq high-throughput sequencing technology was employed to analyze the structure and assembly processes of soil bacterial communities at different pollution levels. Results showed that chromium pollution significantly influences soil properties and soil bacterial communities. The composition and structure of bacterial communities were significantly shifted at different pollution levels. Furthermore, the α diversity of bacterial communities may decrease with relatively high concentrations of chromium. Bacterial communities in chromium polluted soil can be divided into 55 phyla, where Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Firmicutes are the dominant phyla (relative abundance>5%). Moreover, the soil bacterial communities were dominated by the deterministic assembly process (homogeneous selection) and the stochastic ratios decreased with increases in the concentration of chromium in soil. The total concentration of chromium, soil moisture, pH, and organic matter were significantly correlated (P<0.05) with the bacterial communities. Therefore, these soil properties might be the driving factors affecting the structure of bacterial communities.

Microbe mediated arsenic release from iron minerals and arsenic methylation in rhizosphere controls arsenic fate in soil-rice system after straw incorporation.

Arsenic (As) contamination is a global problem. Straw incorporation is widely performed in As contaminated paddy fields. To understand how straw and straw biochar incorporation affect As transformation and translocation in the soil-microbe-rice system, a pot experiment was carried out with different dosages of rice straw and straw biochar application. Results showed that both straw biochar and straw application significantly increased As mobility. Straw biochar mobilized As mainly through increasing soil pH and DOM content. Straw incorporation mainly through enhancing As release from iron (Fe) minerals and arsenate (As(V)) reduction to arsenite (As(III)). Straw biochar didn't significantly affect As methylation, while straw incorporation significantly enhanced As methylation, elevated dimethylarsenate (DMA) concentration in soil porewater and increased As volatilization. Straw biochar didn't significantly change total As accumulation in rice grains, but decreased As(III) accumulation by silicon (Si) inhibition. Straw incorporation significantly increased DMA, but decreased As(III) concentration in rice grains. After biochar application, dissolved As was significantly positively correlated with the abundance of Bacillus, indicating that Bacillus might be involved in As release, and As(III) concentration in polished grains was negatively correlated with Si concentration. The significant positive correlation between dissolved As with Fe and the abundance of iron-reducing bacteria suggested the coupling of As and Fe reduction mediated by iron-reducing bacteria. The significant positive correlation between DMA in rice grains and the abundance of methanogenic bacteria indicated that methanogenic bacteria could be involved in As methylation after straw application. The results of this study would advance the understanding how rice straw incorporation affects As fate in soil-microbe-rice system, and provide some guidance to straw incorporation in As contaminated paddy soil. This study also revealed a wealth of microorganisms in the soil environment that dominate As mobility and transformation after straw incorporation.

[Effects of Rhodopseudomonas palustris PSB06 on Pepper Rhizosphere Microbial Community Structure].

The use of biological pesticide can greatly reduce the soil pollution in the environment. Exploring the effect of biological pesticide on community diversity and distribution of pathogenic bacteria will provide theoretic basis for subsequent researches on biological pesticide micro-ecological control. In order to explore the microbial ecological mechanism of pepper phytophthora blight, this research compared the difference of microbial diversity between rhizosphere soil of infected and healthy plants, and the effects of Rhodopseudomonas palustris PSB06 on microbial diversities of plant rhizosphere soil were investigated using Illumina MiSeq sequencing technology. The results showed that there was less difference in the microbial diversity from the same soil between the seventh day and the fourteenth day. The microbial diversity of rhizosphere soil of healthy plants was higher than that of rhizosphere soil of infected plants. The soil sprayed with Rhodopseudomonas palustris PSB06 exhibited the highest diversity. Moreover, the abundance of Actinomycetes in the rhizosphere soil of healthy plants was higher than that of infected plants, and the highest abundance of Actinomycetes was observed in the soil sprayed with Rhodopseudomonas palustris PSB06. The microbial diversity between rhizosphere soil of infected and healthy plants was significantly different. Spraying Rhodopseudomonas palustris PSB06 could significantly alter the microbial community structure of the soil. It could also increase the diversity of microorganism and the abundance of Actinomycetes in the soil.

[Analysis of Microbial Community in the Membrane Bio-Reactor (MBR) Rural Sewage Treatment System].

Uncontrolled release and arbitrary irrigation reuse of rural wastewater may lead to water pollution, and the microbial pathogens could threaten the safety of freshwater resources and public health. To understand the microbial community structure of rural wastewater and provide the theory for microbial risk assessment of wastewater irrigation, microbial community diversities in the Membrane Bio-Reactor (MBR) process for rural wastewater treatment was studied by terminal restriction fragment length polymorphism (T-RFLP) and 16S rDNA gene clone library. Meanwhile, changes of Arcobacter spp. and total bacteria before and after treatment were detected through real-time quantitative PCR. The clone library results showed that there were 73 positive clones included Proteobacteria (91. 80%), Firmicutes (2. 70%), Bacteroidetes (1. 40%), and uncultured bacteria (4. 10%) in the untreated wastewater. The typical pathogenic genus Arcobacter belonging to e-Proteobacteria was the dominant component of the library, accounting for 68. 5% of all clones. The main groups and their abundance in different treatments were significantly distinct. The highest values of species abundance (S), Shannon-Wiener (H) and Evenness (E) were observed in the adjusting tank, which were 43. 0, 3. 56 and 0. 95, respectively. The real-time quantitative PCR results showed that the copy number of Arcobacter spp. was (1. 09 ± 0. 064 0) x 10(11) copies.L-1 in the untreated sewage, which was consistent with the result of 16S rDNA gene clone library. Compared to untreated wastewater, bacterial copy number in the treated effluent decreased 100 to 1 000 times, respectively, suggesting that MBR treatment system could remove the microbial quantity in such scale. In the recycled water, the physicochemical parameters and indicator bacteria met the water quality standard of farmland irrigation. However, further research is needed to estimate the potential health risks caused by residual pathogenic microorganisms in future.

[Diversity of culturable filamentous bacteria in the activated sludge from A2O wastewater treatment process].

The anoxic-anaerobic-oxic (A2O) process is widely used in wastewater treatment plant, however, sludge bulking and foaming are the most frequent operational problems in this process. Activated sludge bulking is caused by the overgrowth of some types of filamentous bacteria, especially Microthrix parvicella. In the study, 17 strains of filamentous bacteria were isolated from the bulking sludge of A2O process using Gause's medium. The 16S rRNA genes of the 17 isolates were sequenced to analyze their diversity. The results showed all of the 17 isolates were Streptomyces. Further analysis of these strains by the repetitive sequence based on polymerase chain reaction (rep-PCR) technology showed that there was a high diversity in these isolated Streptomyces. The physiological properties of them were different from Microthrix parvicella. The settleability of activated sludge was improved when some of the isolates were inoculated.

Biodegradation of di-n-butyl phthalate by Rhodococcus sp. JDC-11 and molecular detection of 3, 4-phthalate dioxygenase gene.

Rhodococcus sp. JDC-11, capable of utilizing di-n-butyl phthalate (DBP) as the sole source of carbon and energy, was isolated from sewage sludge and confirmed mainly based on 16S rRNA gene sequence analysis. The optimum pH, temperature, and agitation rate for DBP degradation by Rhodococcus sp. JDC-11 was 8.0, 30 degrees C, and 175 rpm, respectively. In addition, the effect of glucose concentration on DBP degradation indicated that low concentration of glucose inhibited the degradation of DBP while high concentrations of glucose increased its degradation. Meanwhile, the substrates utilization test showed that JDC-11 could also utilize other phthalates. Furthermore, the major metabolites of DBP degradation were identified as mono-butyl phthalate and phthalic acid by gas chromatography-mass spectrometry and the metabolic pathway of DBP degradation by Rhodococcus sp. JDC-11 was tentatively speculated. Using a set of new degenerate primer, partial sequence of the 3, 4-phthalate dioxygenase gene was obtained from the strain. Sequence analysis revealed that the phthalate dioxygenase gene of JDC-11 was highly homologous to the large subunit of phthalate dioxygenase from Rhodococcus coprophilus strain G9.

[Isolation and identification of four DBP-degrading strains and molecular cloning of the degradation genes].

Four di-butyl-phthalate(DBP)-degrading bacterial strains, JDC-1, JDC-8, JDC-9 and JDC-12, were isolated from soil. The strains were gram positive. The 16S rRNA sequence analysis revealed that the four strains had similarities of 99% with Arthrobacter sp.. According to the morphologic, physiobiochemical characteristics and the analysis of their 16S rRNA, all the four strains were identified as Arthrobacter sp.. A 900 bp DNA fragment was obtained from the four strains by PCR amplified and clone. When compared with the large subunit of phthalate dioxygenase gene (phtA) of Arthrobacter keyseri, more than 96% similarities were evident in the nucleotide sequences. The optimal growth conditions and degradation rates of DBP were tested and the result indicated that the optimal growth conditions of the four bacteria strains were pH 7.0-8.5 and 30-35 degrees C. All the four bacteria strains performed efficiently for DBP degrading capabilities under optimal conditions. The most efficient strain JDC-1 degraded 500 mg/L DBP completely within 28 h whereas the least efficient strain JDC-8 degraded 500 mg/L DBP completely within 40 h. This study is helpful to the investigation of DBP-degrading mechanisms and the development of microbial resources.