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Plant growth-promoting rhizobacteria (PGPR) can colonize plant root surfaces or form biofilms to promote plant growth and enhance plant resistance to harsh external environments. However, plant–PGPR interactions, especially chemical signaling molecules, are poorly understood. This study aimed to gain an in-depth understanding of the rhizosphere interaction mechanisms between PGPR and tomato plants. This study found that inoculation with a certain concentration of Pseudomonas stutzeri significantly promoted tomato growth and induced significant changes in tomato root exudates. Furthermore, the root exudates significantly induced NRCB010 growth, swarming motility, and biofilm formation. In addition, the composition of the root exudates was analyzed, and four metabolites (methyl hexadecanoate, methyl stearate, 2,4-di-tert-butylphenol, and n-hexadecanoic acid) significantly related to the chemotaxis and biofilm formation of NRCB010 were screened. Further assessment showed that these metabolites positively affected the growth, swarming motility, chemotaxis, or biofilm formation of strain NRCB010. Among these, n-hexadecanoic acid induced the most remarkable growth, chemotactic response, biofilm formation, and rhizosphere colonization. This study will help develop effective PGPR-based bioformulations to improve PGPR colonization and crop yields. [ABSTRACT FROM AUTHOR]

Many problems in drinking water distribution systems (DWDSs) are caused by microbe, such as biofilm formation, biocorrosion and opportunistic pathogens growth. More iron release from corrosion scales may induce red water. Biofilm played great roles on the corrosion. The iron-oxidizing bacteria (IOB) promoted corrosion. However, when iron-reducing bacteria (IRB) and nitrate-reducing bacteria (NRB) became the main bacteria in biofilm, they could induce iron redox cycling in corrosion process. This process enhanced the precipitation of iron oxides and formation of more Fe 3 O 4 in corrosion scales, which inhibited corrosion effectively. Therefore, the IRB and NRB in the biofilm can reduce iron release and red water occurrence. Moreover, there are many opportunistic pathogens in biofilm of DWDSs. The opportunistic pathogens growth in DWDSs related to the bacterial community changes due to the effects of micropollutants. Micropollutants increased the number of bacteria with antibiotic resistance genes (ARGs). Furthermore, extracellular polymeric substances (EPS) production was increased by the antibiotic resistant bacteria, leading to greater bacterial aggregation and adsorption, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in DWDSs. Moreover, O 3 -biological activated carbon filtration-UV-Cl 2 treatment could be used to control the iron release, red water occurrence and opportunistic pathogens growth in DWDSs. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Effects of sulfadiazine and ciprofloxacin on microorganisms in biofilm of drinking water distribution systems (DWDSs) were studied. The results verified that the increases of 16S rRNA for total bacteria and bacterial genus Hyphomicrobium were related to the promotion of antibiotic resistance genes (ARGs) and class 1 integrons (int1) in DWDSs with sulfadiazine and ciprofloxacin. Moreover, the bacteria showed higher enzymatic activities in DWDSs with sulfadiazine and ciprofloxacin, which resulted in more production of extracellular polymeric substances (EPS). The higher contents of EPS proteins and secondary structure β -sheet promoted bacterial aggregation and adsorption onto surface of pipelines to form biofilm. EPS can serve as a barrier for the microorganisms in biofilm. Therefore, the biofilm bacterial communities shifted and the 16S rRNA for total bacteria increased in DWDSs with antibiotics, which also drove the ARGs promotion. Furthermore, the two antibiotics exhibited stronger combined effects than that caused by sulfadiazine and ciprofloxacin alone. Graphical abstract Image 1 Highlights • Response of biofilm to sulfadiazine and ciprofloxacin in DWDSs was studied. • Bacterial community shift and total bacteria increase related to ARGs promotion. • The bacteria exhibited higher enzymatic activity and produced more EPS. • The higher contents of proteins and β -sheet in EPS promoted biofilm formation. • Sulfadiazine and ciprofloxacin exhibited stronger combined effects on biofilm. [ABSTRACT FROM AUTHOR]

Biofilm bacterial communities and cast iron corrosion were studied in bench-scale reactors with chloraminated drinking water. Before 6 d, α-FeOOH was predominant in corrosion scales, and the main bacterial genera were Acidovorax and Aquabacterium with higher iron corrosion and release. After this point, Fe 3 O 4 was formed, and Azospira and Dechloromonas became the main bacterial genera with lower iron corrosion and release. Principal component analysis (PCA) showed good correlation among the bacterial genera, corrosion rate, and the content of α-FeOOH and Fe 3 O 4 in corrosion scales. Moreover, most probable number (MPN) enumerations indicated that the main nitrate-reducing bacteria (NRB), iron-oxidizing bacteria (IOB) and iron-reducing bacteria (IRB), could induce oxidation of Fe(II) and reduction of Fe(III) inside the corrosion scales. It was also verified that the process of Fe redox possibly induced by these microorganism respiration, could drive the transformation of α-FeOOH to Fe 3 O 4 . This resulted in higher inhibition of iron corrosion and release in chloraminated drinking water than that in sterile water. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of UV on corrosion and water quality stability were investigated. [•] UV pretreatment reduced the required initial chlorine dose. [•] The corrosion bacteria grew selectively with different disinfection processes. [•] UV irradiation resulted in lower corrosion rate. [•] UV irradiation enhanced water quality stability in the RWDS. [ABSTRACT FROM AUTHOR]

Abstract: The effects of disinfection and biofilm on the corrosion of cast iron pipe in a model reclaimed water distribution system were studied using annular reactors (ARs). The corrosion scales formed under different conditions were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM), while the bacterial characteristics of biofilm on the surface were determined using several molecular methods. The corrosion scales from the ARs with chlorine included predominantly α-FeOOH and Fe2O3, while CaPO3(OH)·2H2O and α-FeOOH were the predominant phases after chloramines replaced chlorine. Studies of the consumption of chlorine and iron release indicated that the formation of dense oxide layers and biofilm inhibited iron corrosion, causing stable lower chlorine decay. It was verified that iron-oxidizing bacteria (IOB) such as Sediminibacterium sp., and iron-reducing bacteria (IRB) such as Shewanella sp., synergistically interacted with the corrosion product to prevent further corrosion. For the ARs without disinfection, α-FeOOH was the predominant phase at the primary stage, while CaCO3 and α-FeOOH were predominant with increasing time. The mixed corrosion-inducing bacteria, including the IRB Shewanella sp., the IOB Sediminibacterium sp., and the sulfur-oxidizing bacteria (SOB) Limnobacter thioxidans strain, promoted iron corrosion by synergistic interactions in the primary period, while anaerobic IRB became the predominant corrosion bacteria, preventing further corrosion via the formation of protective layers. [Copyright &y& Elsevier]

The effects of ozone-biologically activated carbon (O 3 -BAC) treatment with various phosphate doses (0, 0.3 or 0.6 mg/L) were investigated on the formation of disinfection by-products (DBPs) and occurrence of opportunistic pathogens (OPs) in drinking water distribution systems (DWDSs) simulated by annular reactors (ARs). It was found that the lowest DBPs and the highest inactivation of OPs such as Mycobacterium spp. , Mycobacterium avium , Aeromonas spp. , Pseudomonas aeruginosa and Hartmanella vermiformis , occurred in the effluent of the AR with 0.6 mg/L phosphate addition. Based on the results of different characterization techniques, for the AR with 0.6 mg/L phosphate-enhanced O 3 -BAC treatment, dissolved organic carbon in the influent exhibited the lowest concentration and most stable fraction due to the improved biodegradation effect. Moreover, the total amount of suspended extracellular polymeric substances (EPS) in the bulk water of the AR decreased greatly, resulting in the lowest chlorine consumption and DBPs formation in the AR. In Fourier transform infrared spectra of the suspended EPS, the amide II band (1600-1500 cm −1 ) disappeared and the protein/polysaccharide ratio decreased remarkably, indicating the destruction of protein and a decrease in hydrophobicity. Moreover, β-sheets and α-helices in the protein secondary structures were degraded while the random coils increased sharply as phosphate addition increased to 0.6 mg/L, inhibiting microbial aggregation and hence weakening the chlorine-resistance capability. Thus, most of the OPs in suspended biofilms were more easily inactivated by residual chlorine, resulting in the lowest OPs occurrence in the effluent of the AR. Our findings indicated that enhancing the efficiency of the BAC filter by adding phosphate is a promising method for improving water quality in DWDSs. [ABSTRACT FROM AUTHOR]

The effects of disinfection efficiency on microbial communities and the corrosion of cast iron pipes in drinking water distribution systems (DWDSs) were studied. Two annular reactors (ARs) that simulated actual running conditions with UV/Cl 2 disinfection and chlorination alone were used. High chlorine consumption and corrosion rate were found in the AR with UV/Cl 2. According to functional genes and pyrosequencing tests, a high percentage of iron recycling bacteria was detected within the biofilm of the AR with Cl 2 at early running stage, whereas siderophore-producing bacteria were dominant in the biofilm of the AR with UV/Cl 2. At the early running stage, the sequential use of UV light and an initial high chlorine dosage suppressed the biomass and iron-recycling bacteria in both bulk water and biofilms, thereby forming less protective scales against further corrosion, which enhanced chlorine consumption. Non-metric multidimensional scaling analysis showed that the bacterial communities in the ARs shaped from within rather than being imported by influents. These results indicate that the initial high disinfection efficiency within the distribution system had not contributed to the accumulation of iron-recycling bacteria at the early running stages. This study offer certain implications for controlling corrosion and water quality in DWDSs. Image 1 [ABSTRACT FROM AUTHOR]

Red water has occasionally been observed in the water distribution system of Beijing following a change in the city's water source. Aged cast iron pipes from both affected and unaffected areas were used to establish experimental drinking water distribution systems under different disinfection conditions. The scale deposits formed under different conditions were characterized by X-ray diffraction and scanning electron microscopy, and the bacterial characteristics of the corrosion scales were determined using several molecular methods. The water quality changed less in pipe samples from the unaffected areas than pipes from the affected areas. The pipe samples from the unaffected area included predominantly α-FeOOH, Fe 3 O 4 , and γ-FeOOH, and 24.2% nitrate-reducing bacteria (NRB) were predominant with fewer iron-oxidizing bacteria (IOB) being observed. The composition of corrosion products did not exhibit large variation over time although their crystallinity exhibited a slight decrease throughout the duration of the experiment. In contrast, in the pipe samples from the affected, α-FeOOH was the main compound with less γ-FeOOH and Fe 3 O 4 , and 3.3% IOB and 12% NRB with few IRB were observed. However, after transporting surface water containing disinfectants, the Fe 3 O 4 and dense corrosion layer formed, inhibiting the release of iron. Moreover, IRB and NRB became dominant. 22.6% and 34.3% NRB appeared in the pipes after chlorination and chloramination, respectively. The synergistic interaction of IRB and NRB with the corrosion layer played a large role in the release of iron from a cast iron pipe following changes in water quality. [ABSTRACT FROM AUTHOR]

The effect of chlorine and chloramine disinfection on bacterial communities and the corrosion of cast iron pipes was studied in drinking water distribution systems (DWDSs) transporting groundwater. α-FeOOH was the main corrosion product for both systems. However, loose corrosion products were formed in DWDSs with chlorine, whereas dense crystallized particles were formed in DWDSs with chloramine. Based on the functional genes and pyrosequencing assay results, both DWDSs had different compositions of corrosion-related bacteria in the bulk water and biofilms. The percentage of total denitrifying gene copy numbers in the 16S rRNA and the bacterial diversities were much higher at 220 d within the bulk water and biofilm in DWDSs disinfected with chloramine compared with those disinfected with chlorine. Most of the NO 3 − –N in the raw water was biologically denitrified through chlorine DWDSs in the experimental period, whereas the same phenomena occurred only when denitrifying bacteria were increased in the effluent due to the role of autotrophic microbial nitrification in chloramine DWDSs. Furthermore, nitrate-dependent Fe(II) oxidation occurred to a greater extent, leading to denser corrosion scales in DWDSs with chloramine compared with those disinfected with chlorine. [ABSTRACT FROM AUTHOR]

Abstract: The effect of UV/Cl2 disinfection on the biofilm and corrosion of cast iron pipes in drinking water distribution system were studied using annular reactors (ARs). Passivation occurred more rapidly in the AR with UV/Cl2 than in the one with Cl2 alone, decreasing iron release for higher corrosivity of water. Based on functional gene, pyrosequencing assays and principal component analysis, UV disinfection not only reduced the required initial chlorine dose, but also enhanced denitrifying functional bacteria advantage in the biofilm of corrosion scales. The nitrate-reducing bacteria (NRB) Dechloromonas exhibited the greatest corrosion inhibition by inducing the redox cycling of iron to enhance the precipitation of iron oxides and formation of Fe3O4 in the AR with UV/Cl2, while the rhizobia Bradyrhizobium and Rhizobium, and the NRB Sphingomonas, Brucella producing siderophores had weaker corrosion-inhibition effect by capturing iron in the AR with Cl2. These results indicated that the microbial redox cycling of iron was possibly responsible for higher corrosion inhibition and lower effect of water Larson–Skold Index (LI) changes on corrosion. This finding could be applied toward the control of water quality in drinking water distribution systems. [Copyright &y& Elsevier]