Responses of Soil Microbial Survival Strategies and Functional Changes to Wet-Dry Cycle Events.

Soil microbial taxa have different functional ecological characteristics that influence the direction and intensity of plant-soil feedback responses to changes in the soil environment. However, the responses of soil microbial survival strategies to wet and dry events are poorly understood. In this study, soil physicochemical properties, enzyme activity, and high-throughput sequencing results were comprehensively anal0079zed in the irrigated cropland ecological zone of the northern plains of the Yellow River floodplain of China, where Oryza sativa was grown for a long period of time, converted to Zea mays after a year, and then Glycine max was planted. The results showed that different plant cultivations in a paddy-dryland rotation system affected soil physicochemical properties and enzyme activity, and G. max field cultivation resulted in higher total carbon, total nitrogen, soil total organic carbon, and available nitrogen content while significantly increasing α-glucosidase, ß-glucosidase, and alkaline phosphatase activities in the soil. In addition, crop rotation altered the r/K-strategist bacteria, and the soil environment was the main factor affecting the community structure of r/K-strategist bacteria. The co-occurrence network revealed the inter-relationship between r/K-strategist bacteria and fungi, and with the succession of land rotation, the G. max sample plot exhibited more stable network relationships. Random forest analysis further indicated the importance of soil electrical conductivity, total carbon, total nitrogen, soil total organic carbon, available nitrogen, and α-glucosidase in the composition of soil microbial communities under wet-dry events and revealed significant correlations with r/K-strategist bacteria. Based on the functional predictions of microorganisms, wet-dry conversion altered the functions of bacteria and fungi and led to a more significant correlation between soil nutrient cycling taxa and environmental changes. This study contributes to a deeper understanding of microbial functional groups while helping to further our understanding of the potential functions of soil microbial functional groups in soil ecosystems.

Integrative conjugative elements mediate the high prevalence of tmexCD3-toprJ1b in Proteus spp. of animal source.

IMPORTANCE: The emergence and spread of tmexCD-toprJ have greatly weakened the function of tigecycline. Although studies have demonstrated the significance of Proteus as carriers for tmexCD-toprJ, the epidemic mechanism and characteristics of tmexCD-toprJ in Proteus remain unclear. Herein, we deciphered that the umuC gene in VRIII of SXT/R391 ICEs was a hotspot for the integration of tmexCD3-toprJ1b-bearing mobile genetic elements by genomic analysis. The mobilization and dissemination of tmexCD3-toprJ1b in Proteus were mediated by highly prevalent ICEs. Furthermore, the co-occurrence of tmexCD3-toprJ1b-bearing ICEs with other chromosomally encoded multidrug resistance gene islands warned that the chromosomes of Proteus are significant reservoirs of ARGs. Overall, our results provide significant insights for the prevention and control of tmexCD3-toprJ1b in Proteus.

Epidemiological and Molecular Characteristics of bla NDM-1 and bla KPC-2 Co-Occurrence Carbapenem-Resistant Klebsiella pneumoniae.

Objective: Carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged and spread worldwide. It can usually cause a serious threat complicating treatment options in clinical settings. However, treatment options are limited. The present study investigates the prevalence and genetic characteristics of bla NDM-1 and bla KPC-2 co-harboring clinical isolates of Klebsiella pneumoniae. Methods: In this study, Multiplex polymerase chain reaction (PCR) was performed to detect the carbapenem-resistant genes, and the broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of antibacterial drugs. The transferability of carbapenem-resistant phenotypes was examined using filter mating assays. Overall, we used Illumina sequencing to evaluate the epidemiological and molecular characteristics of bla NDM-1 and bla KPC-2 (genes encoding carbapenemase) co-occurrence in CRKP strains. Results: All strains exhibited resistance to carbapenems and other antibiotics. However, they were still susceptible to polymyxin E. Among them, 18 isolates were positive for bla KPC-2, bla NDM-1, and multiple virulence determinants, such as genes encoding the virulence factor aerobactin, yersiniabactin, and the regulator of the mucoid phenotype (rmpA and rmpA2). Whole genome sequencing revealed that the 18 CRKP strains belonged to ST11 and capsular serotype KL64, and could be grouped into two evolutionary branches. Furthermore, these strains displayed hypervirulence potential since all of them carried pLVPK-like plasmid. Conclusion: These findings suggested that ST11-KL64 CRKP strains are major threats in terms of nosocomial infections in this hospital. Hence, new strategies should be urgently developed to monitor, diagnose, and treat this high-risk CRKP clone.

A novel method of simultaneous NH4+ and NO3- removal using Fe cycling as a catalyst: Feammox coupled with NAFO.

The feasibility of using Feammox coupled with nitrate-dependent Fe(II) oxidizing (NAFO) to cause the simultaneous conversion of NH4+ and NO3- was explored by inoculation with Feammox sludge and the use Fe cycling as catalyst. After 61days operation, the simultaneous conversion of NO3- and NH4+ occurred with the presence of interconversion between Fe(III) and Fe(II). The conversion ratio of NH4+ to NO3- stabilized at 0.9-1. The results of isotopic tracing and microbial diversity analysis indicated that NH4+ was first oxidized to NO2- by Fe(III), then NO3- was reduced to NO2- and N2 by the Fe(II) produced in Feammox process, and finally, the NO2- produced in NAFO process underwent an Anammox process with the remaining NH4+ to yield N2. The results showed the simultaneous continuous conversion process of NO3- and NH4+ with limited Fe as a catalyst was a coupled process of Feammox, Anammox, and NAFO under the anaerobic conditions.