In recent years, the global carbon cycle has garnered significant research attention. However, details of the intricate relationship between planktonic bacteria, hydrochemistry, and dissolved organic matter (DOM) in inland waters remain unclear, especially their effects on lake carbon sequestration. In this study, we analyzed 16S rRNA, chromophoric dissolved organic matter (CDOM), and inorganic nutrients in Erhai Lake, Yunnan Province, China. The results revealed that allochthonous DOM (C3) significantly regulated the microbial community, and that autochthonous DOM, generated via microbial mineralization (C2), was not preferred as a food source by lake bacteria, and neither was allochthonous DOM after microbial mineralization (C4). Specifically, the correlation between the fluorescence index and functional genes (FAPRPTAX) showed that the degree of utilization of DOM was a critical factor in regulating planktonic bacteria associated with the carbon cycle. Further examination of the correlation between environmental factors and planktonic bacteria revealed that Ca2+ had a regulatory influence on the community structure of planktonic bacteria, particularly those linked to the carbon cycle. Consequently, the utilization strategy of DOM by planktonic bacteria was also determined by elevated Ca2+ levels. This in turn influenced the development of specific recalcitrant autochthonous DOM within the high Ca2+ environment of Erhai Lake. These findings are significant for the exploration of the stability of DOM within karst aquatic ecosystems, offering a new perspective for the investigation of terrestrial carbon sinks.

Methicillin-resistant Staphylococcus aureus (M RSA) infections, in particular biofilm-organized bacteria, remain a clinical challenge and a serious health problem. Rifabutin (RFB), an antibiotic of the rifamycins class, has shown in previous work excellent anti-staphylococcal activity. Here, we proposed to load RFB in liposomes aiming to promote the accumulation of RFB at infected sites and consequently enhance the therapeutic potency. Two clinical isolates of MRSA, MRSA-C1 and MRSA-C2, were used to test the developed formulations, as well as the positive control, vancomycin (VCM). RFB in free and liposomal forms displayed high antibacterial activity, with similar potency between tested formulations. In MRSA-C1, minimal inhibitory concentrations (MIC) for Free RFB and liposomal RFB were 0.009 and 0.013 μg/mL, respectively. Minimum biofilm inhibitory concentrations able to inhibit 50% biofilm growth (MBIC50) for Free RFB and liposomal RFB against MRSA-C1 were 0.012 and 0.008 μg/mL, respectively. Confocal microscopy studies demonstrated the rapid internalization of unloaded and RFB-loaded liposomes in the bacterial biofilm matrix. In murine models of systemic MRSA-C1 infection, Balb/c mice were treated with RFB formulations and VCM at 20 and 40 mg/kg of body weight, respectively. The in vivo results demonstrated a significant reduction in bacterial burden and growth index in major organs of mice treated with RFB formulations, as compared to Control and VCM (positive control) groups. Furthermore, the VCM therapeutic dose was two fold higher than the one used for RFB formulations, reinforcing the therapeutic potency of the proposed strategy. In addition, RFB formulations were the only formulations associated with 100% survival. Globally, this study emphasizes the potential of RFB nanoformulations as an effective and safe approach against MRSA infections.

Planktonic bacterial presence in many industrial and environmental applications and personal health-care products is generally countered using antimicrobials. However, antimicrobial chemicals present an environmental threat, while emerging resistance reduces their efficacy. Suspended bacteria have no defense against mechanical attack. Therefore, we synthesized silica hexapods on an α-Fe2O3 core that can be magnetically-rotated to inflict lethal cell-wall-damage to planktonic Gram-negative and Gram-positive bacteria. Hexapods possessed 600 nm long nano-spikes, composed of SiO2, as shown by FTIR and XPS. Fluorescence staining revealed cell wall damage caused by rotating hexapods. This damage was accompanied by DNA/protein release and bacterial death that increased with increasing rotational frequency up to 500 rpm. Lethal puncturing was more extensive on Gram-negative bacteria than on Gram-positive bacteria, which have a thicker peptidoglycan layer with a higher Young\'s modulus. Simulations confirmed that cell-wall-puncturing occurs at lower nano-spike penetration levels in the cell walls of Gram-negative bacteria. This approach offers a new way to kill bacteria in suspension, not based on antimicrobial chemicals.

Planktonic bacteria play a crucial role in sustaining the ecological balance of aquatic ecosystems. However, their seasonal variations in different aquaculture areas within the East China Sea, along with their correlation to environmental factors, have not been extensively explored. In this study, each area with 3 sample points were set up to represent the fish aquaculture area, shellfish aquaculture area and non-aquaculture area. In 2019, we undertook four marine surveys along the Xiasanhengshan uninhabited island, during which we gathered surface seawater samples for both physicochemical analysis and high-throughput sequencing. This allowed us to obtain data about the physicochemical properties and microbial composition in each surveyed region. A short-term eutrophication phenomenon was present in the sea, and the spatial and temporal distribution of planktonic bacteria differed based on the mariculture area. At the phylum level, Proteobacteria accounted for >50 % of the community abundance in winter, spring, and autumn, while Cyanobacteria accounted for >30 % of the community abundance in summer. Because Cyanobacteria blooms are likely in summer, the relationship between Cyanobacteria and environmental factors was studied. Redundancy analysis showed that Cyanobacteria were consistently positively correlated with phosphate. Eutrophication and abnormal proliferation of Cyanobacteria in the study area necessitate ameliorations in the mariculture structure. The variation of genus in Proteobacteria is consistent with that of eutrophication, so some genera in Proteobacteria have the potential to become biological indicator species.

A combined temporal and spatial research approach helps us to evaluate the ecological status of a river scientifically and comprehensively. To understand the response mechanisms of bacteria in the Li River to different environments, we conducted a 1-year study (2020-2021) and collected water samples from 18 sections of the river in October, January, April, and August. 16S sequencing was used to study the composition and structure of bacterial communities in Li River at different temporal and spatial scales. The results showed that NO3--N, TP, T, pH, and DO were significantly different on spatial and temporal scales. Alpha diversity of planktonic bacteria in Li River fluctuated significantly with the season, reaching its highest in summer. Proteobacteria remained the most dominant phylum in all seasons, but the differential microorganisms varied between seasons. Although the abundance of metabolic functions of planktonic bacteria did not show significant differences between seasons, we found that DO, TP, T, and COD were the key environmental factors affecting bacterial metabolism. In addition, the co-occurrence network analysis showed that the autumn network had a higher number of nodes and edges and exhibited a high degree of complexity, while the summer network had the highest degree of modularity and exhibited greater stability. These results deepen our knowledge of the response mechanisms of river microorganisms to temporal and spatial changes and provide a scientific reference for the study of river ecosystems.

UNASSIGNED: Pseudomonas aeruginosa (P. aeruginosa) can cause serious infections in many parts of the body and is also an underestimated foodborne pathogen. Intense pulsed light sterilization is recognized for its high sterilization efficiency, flexible and safe operation and ease of installation on production lines, which makes up for the shortcomings of several other physical sterilization technologies.
UNASSIGNED: This experiment studied the killing efficiency of different capacitances (650 μF, 470 μF, and 220 μF) of intense pulsed light on foodborne pathogenic microorganisms P. aeruginosa in the models of liquid food models, 96-well cell plates, and polycarbonate membrane models at room temperature (25°C) and refrigerated (4°C) environments to provide data to support the application of IPL sterilization devices in food processing.
UNASSIGNED: The IPL was very effective in killing P. aeruginosa in the planktonic state as well as in the early and mature biofilm states, meeting target kill rates of 100%, 99.99%, and 94.33% for a given number of exposures. The biofilms formed in the polycarbonate membrane model and the 96-well plate model were more resistant to killing compared to the planktonic state. To achieve the same bactericidal effect, the number of flashes increased with decreasing capacitance.
UNASSIGNED: The bactericidal effect of IPL on P. aeruginosa was significantly influenced by the state of the bacterium. The larger the capacitance the higher the number of pulses and the better the sterilization effect on P. aeruginosa.

The overuse and improper disposal of antibiotics results in antibiotic resistance. This raises concern over the presence of antibiotic resistant bacteria (ARB) in waterways and pose health risks of antibiotic resistant infections to water recreationists. The purpose of this study was to monitor water quality, microbial ecology, and antibiotic resistance in water and biofilm on submerged plastics at two public boat launches in southeastern Louisiana. Water and biofilm samples were collected once a month, in triplicate, from two public boat launches in Louisiana, USA for a year. Water quality metrics included nitrate, ammonia, sulfate, phosphate, and organic carbon. Water samples were tested for total and fecal coliform abundance and the presence of ARB. Out of 131 bacterial isolates studied from these two sites, 86% of them tested positive for antibiotic resistance with multi-drug resistance. Antibiotic resistance genes (ARGs) for sulfonamide (sul2), bacitracin (bacA) and ampicillin (ampA) were identified in bacterial isolates from water and biofilm samples at both sites. Molecular genetic diversity analysis identified distinct taxonomic diversity differences in biofilm bacteria compared to the planktonic bacteria in the surrounding water. Biofilm samples showed increased diversity at the phylum, genus, and species levels.

Planktonic bacteria are an important part of aquatic ecosystems and interact with zooplankton. However, it is still unclear whether different planktonic bacteria differentially interfere with the responses of zooplankton to their predators. Here, we investigated the effects of different planktonic bacteria, which were isolated and purified from natural lakes, on the anti-predation (Rhodeus ocellatus as the predator) defense responses of Daphnia magna. Our results showed that the effects of planktonic bacteria on the induced life-history defenses of Daphnia were species-specific. Bacteria which increased (e.g., Escherichia coli, Citrobacter braakii) Daphnia body size also promoted the induced defense of body size, whereas bacteria which decreased (e.g., Pseudomonas spp.) Daphnia body size also inhibited the induced defense of body size. In addition, the same bacteria had different effects on induced defense traits. Some bacteria (e.g., E. coli) promoted the induced defense of body size but reduced the induced defense of offspring number, whereas other bacteria (e.g., Aeromonas hydrophila, Aeromonas veronas) weakened the induced defense of body size but had no significant effect on the induced defense of offspring number. Moreover, the differential effects of planktonic bacteria on Daphnia\'s induced defenses were not related to the bacterial degradation of kairomone. This study illustrated, for the first time, the species-specific effects of planktonic bacteria on predator-induced responses of Daphnia. IMPORTANCE This study is the first to reveal the differential effects of different species of planktonic bacteria on fish kairomone-induced defense traits and energy redistribution in Daphnia. Our results not only help deepen the understanding of Daphnia\'s inducible defenses in environments containing a variety of bacteria but also provide insights into the energy reallocation involved in anti-predator defenses.

Floodplains play essential roles in the ecological functions of regional environments. The merging and coalescence of bacterial communities in aquatic environments results in periodic patterns driven by regular hydrological activities, which may, in turn, influence ecological activities. However, the degree of bacterial community coalescence in the lateral and vertical directions as well as the underlying hydrological mechanism of floodplain ecosystems is poorly understood. Therefore, we investigated the spatiotemporal patterns and coalescence processes of planktonic and sedimentary bacterial communities during normal and high-water periods in a floodplain ecosystem of the Yellow River source region. We classified bacterial operational taxonomic units (OTUs) based on 16S rRNA gene sequencing, and quantified community coalescence by calculating the proportions of overlapping OTUs, the contributions of upstream sources to downstream sinks, and positive/negative cohesion. The results revealed major differences in the composition and diversity of planktonic and sedimentary bacterial communities. Bacterial community diversity in the high-water period was higher than in the normal period. Laterally, hydrological connectivity promoted the immigration and coalescence of bacterial communities to oxbow lakes in both the mainstream and tributaries, with the coalescence degree of planktonic bacteria (2.9%) higher than that of sedimentary bacteria (1.7%). Vertically, the coalescence degree of mainstream planktonic and sedimentary bacterial communities was highest, reaching 2.9%. Co-occurrence network analysis revealed that hydrological connectivity increased the complexity of the bacterial network and enhanced the coalescence of keystone species to oxbow lakes. Furthermore, community coalescence improved the competitiveness and dispersal of bacterial communities. This study demonstrated that coalescence of bacterial communities is driven by hydrological connectivity in a floodplain ecosystem. Further studies should investigate the processes of bacterial community coalescence in floodplains in more detail, which could provide new approaches for environmental protection and ecological function preservation.

Biological carbon pump (BCP) in karst areas has received intensive attention for years due to their significant contribution to the global missing carbon sink. The stability of autochthonous dissolved organic matter (Auto-DOM) produced by BCP in karst aquatic ecosystems may play a critical role in the missing carbon sink. However, the source of dissolved organic matter (DOM) in inland waters and its consumption by planktonic bacteria have not been thoroughly examined. Recalcitrant dissolved organic matter (RDOM) may exist in karst aquatic ecosystem as in the ocean. Through the study of the chromophoric dissolved organic matter (CDOM) and the interaction between CDOM and the planktonic bacterial community under different land uses at the Shawan Karst Water-carbon Cycle Test Site, SW China, we found that C2, as the fluorescence component of Auto-DOM mineralised by planktonic bacteria, may have some of the characteristics of RDOM and is an important DOM source in karst aquatic ecosystems. The stability ratio (Fmax(C2/(C1+C2))) of Auto-DOM reached 89.6 ± 6.71% in winter and 64.1 ± 7.19% in spring. Moreover, correlation-based network analysis determined that the planktonic bacterial communities were controlled by different fluorescence types of CDOM, of which C1 (fresh Auto-DOM), C3 (conventional allochthonous DOM (Allo-DOM)) and C4 (the Allo-DOM mineralised by bacteria) were clustered in one module together with prevalent organic-degrading planktonic bacteria; C2 was clustered in another tightly combined module, suggesting specific microbial utilization strategies for the C2 component. In addition, some important planktonic bacterium and functional genes (including chemotrophic heterotrophs and photosynthetic bacteria) were found to be affected by high Ca2+ and dissolved inorganic carbon (DIC) concentrations in karst aquatic ecosystems. Our research showed that Auto-DOM may be as an important carbon sink as the Allo-DOM in karst ecosystems, the former generally being neglected based on a posit that it is easily and first mineralized by planktonic bacteria.