[Metagenomic Analysis Provides Insights into Bacterial Communities, Antibiotic Resistomes, and Public Health Risks in the Dongping Lake Reservoir].

Owing to the long residence times of water, water reservoirs readily contribute to the accumulation of antibiotic resistant gene (ARG). It is of great public health significance to explore bacterial communities, antibiotic resistomes, and the potential public health risks of water reservoirs. In this study, metagenomic sequencing was used to analyze and compare the bacterial communities, ARG profiles, ARG-horizontal transfer, and ARG-carrying pathogens in the water and sediments of the Dongping Lake Reservoir in the dry and the wet seasons. Compared with that of the sediments, the results showed that both the bacterial communities and ARG profiles in the water were significantly influenced by the seasons, and the total ARG abundance in the dry season was significantly higher than that in the wet season. The total ARG abundance in the sediments was higher than that in water, but the horizontal transfer potential of ARG in the water was higher than that in the sediment. A total of 377 ARG subtypes belonging to 20 ARG types were found in this study. Bacitracin and vancomycin resistance genes were the main ARG types in the water and sediments, respectively, and Proteobacteria and Actinobacteria were the major ARG-carrying bacteria in the water and sediments, respectively. In addition, 30 clinical pathogens carrying ARGs were identified, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica, and Acinetobacter bohemicus. More importantly, two Escherichia coli concurrently carried virulence factor and ARG. In summary, this study revealed that a variety of ARG types existed in the Dongping Lake Reservoir, which has posed potential public health risks by contributing to the horizontal transfer of ARG and the accumulation of clinical pathogens. Therefore, it is necessary to regularly monitor the bacterial community and ARG profile in various water bodies.

[Colonization of grape leaves by endophytic Bacillus subtilis JL4 and its control of grape downy mildew]. / å† ç”Ÿæž¯è‰èŠ½å­¢æ†èŒJL4åœ¨è‘¡è„å¶ä¸Šçš„å®šæ®–åŠå ¶å¯¹è‘¡è„éœœéœ‰ç— çš„é˜²æ²».

In order to understand the colonization pattern of Bacillus subtilis JL4 both on and inside grape leaves, and its control of grape downy mildew, a shuttle vector pGFP78, carrying the GFP gene, was transformed into B. subtilis JL4, and a GFP-labelled transformant designated as JL4-gfp was obtained successfully. The stability of the marker and antagonistic activity to Plasmopara viticola of JL4-gfp were tested. JL4-gfp was spray inoculated on grape leaves in a vine yard and colonization of the leaves was investigated by dilution plating on selective medium. Leaves treated with JL4-gfp were collected and taken to the laboratory for inoculation of a sporangial suspension of P. viticola, to determine its control effect on grape downy mildew. The green fluorescence of the marked strain was stable for at least 10 subcultures, and JL4-gfp maintained wild type antagonistic activity against P. viticola. JL4-gfp was recovered from the grape leaves by dilution plating on medium supplemented with antibiotics. Numbers recovered from the leaf surface of grape leaves were 3.6×105, 2.7×105 and 3.1×103 CFU·g-1 at 0, 3 and 7 days after inoculation, and the population density inside the leaf tissue reached a maximum of 9.6×104 CFU·g-1 at 3 days after inoculation, but could not be recovered after 14 days. The efficiency of downy mildew control by the marked strain was more than 88.0% at 3 days after inoculation, but no significant control effect was observed after 7 days. Our results suggested that there was a positive correlation between the JL4-gfp population density and control efficiency of grape downy mildew, and a threshold colonization level at 105 CFU·g-1 was a prerequisite for this Bacillus strain to present efficient control effects.