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Interfacial oscillation associated with direct contact condensation of steam jet in water pipe flow is of high significance for industrial processes. In this paper, experimental study is conducted to reveal the mechanisms of the interfacial oscillation in steam jet condensation in subcooled water flow in a vertical pipe. The interfacial behavior of the jet plume is acquired by high speed camera, and the entire interface in both space and time simultaneously is quantitatively analyzed with digital image processing technology. Bubbling regime occurs at subsonic conditions, where an undulated bubble plume forms with one or more large bubbles falling off intermittently. Jetting regime happens at transonic or supersonic conditions, where a quasi-stable jet plume is observed with numerous uncondensed tiny bubbles continuously shedding off from the end of the jet plume. Distinct waveforms of the radial interface position in both space and time simultaneously are recognized for the two typical condensation regimes. The interfacial unsteadiness reaches a maximum near the sonic point and then drops in the supersonic region, which exhibits similar trend with pressure oscillation induced by condensing jet in a qualitative sense. The results confirm that the pressure oscillation is highly relevant to the motion of the jet interface and it should be induced by the interfacial oscillation. The spatial growth rate of the interface unsteadiness along the jet decreases steadily as steam mass flux increases from subsonic to sonic point and it almost does not vary in the supersonic region. The Kelvin-Helmholtz instability mechanism is more important near the nozzle exit, while in other region the Kelvin-Helmholtz instability is of the same importance as the Rayleigh-Taylor instability.

Bone marrow-derived mesenchymal stem cells (MSCs) improve cardiac function after ischemia/reperfusion injury, in part, due to the release of cytoprotective paracrine factors. Toll-like receptor 4 (TLR4) is expressed in MSCs and regulates the expression of cytoprotective factors, cytokines, and chemokines. Lipopolysaccharide (LPS) stimulation of TLR4 activates two distinct signaling pathways that are either MyD88 dependent or MyD88 independent/TIR-domain-containing adapter-inducing interferon-β (TRIF) dependent. While it was reported previously that LPS treatment improved MSC-mediated cardioprotection, the mechanism underlying such improved effect remains unknown. To study the role of MyD88 signaling in MSC cardioprotective activity, wild type (WT) and MyD88(−/−) MSCs were treated with LPS (200 ng/mL) for 24 h. WT and MyD88(−/−) MSCs with or without LPS pretreatment were infused into the coronary circulation of isolated mouse hearts (Langendorff model) and then subjected to ischemia (25 min) and reperfusion (50 min). Saline served as a negative control. Both untreated and LPS-pretreated WT MSCs significantly improved postischemic recovery of myocardial function of isolated mouse hearts, as evidenced by improved left ventricular developed pressure and ventricular contractility assessment (ie, the rate of left ventricle pressure change over time, ± dp/dt). LPS-pretreated WT MSCs conferred better cardiac function recovery than untreated MSCs; however, such effect of LPS was abolished when using MyD88(−/−) MSCs. In addition, LPS stimulated stat3 activity in WT MSCs, but not MyD88(−/−) MSCs. stat3 small interfering RNA abolished the effect of LPS in improving the cardioprotection of WT MSCs. In conclusion, this study demonstrates that LPS improves MSC-mediated cardioprotection by MyD88-dependent activation of stat3.

T helper cell differentiation requires lineage-defining transcription factors and factors that have shared expression among multiple subsets. BATF is required for development of multiple Th subsets but functions in a lineage-specific manner. BATF is required for IL-9 production in Th9 cells but in contrast to its function as a pioneer factor in Th17 cells, BATF is neither sufficient nor required for accessibility at the Il9 locus. Here we show that STAT5 is the earliest factor binding and remodeling the Il9 locus to allow BATF binding in both mouse and human Th9 cultures. The ability of STAT5 to mediate accessibility for BATF is observed in other Th lineages and allows acquisition of the IL-9-secreting phenotype. STAT5 and BATF convert Th17 cells into cells that mediate IL-9-dependent effects in allergic airway inflammation and anti-tumor immunity. Thus, BATF requires the STAT5 signal to mediate plasticity at the Il9 locus., BATF is a transcription factor that is needed for IL-9 production by T helper 9 cells. Here the authors show that STAT5 is needed at the Il9 locus to enable BATF to function in this manner and that this interaction can reprogram other T helper subsets into IL-9 producing cells, thus regulating the immune response to disease.

Background: Early human heart and brain development simultaneously occur during embryogenesis. Notably, in human newborns, congenital heart defects strongly associate with neurodevelopmental abnormalities, suggesting a common gene/complex underlying both cardiogenesis and neurogenesis. However, due to lack of in vivo studies, the molecular mechanisms that govern both early human heart and brain development remain elusive. The evolutionarily conserved ATP-dependent SWI/SNF complex is one of the largest chromatin remodeling complexes, consisting of ~15 subunits, including SMARCA2 (also known as BRM) or SMARCA4 (also known as BRG1) as the ATPase catalytic subunit. Several BRG1-associated factors (BAFs), such as ARID1A (Baf250a), have DNA binding capacity and assemble with either BRM or BRG1 to form a functional chromatin-remodeling complex. A single amino acid mutation (Arid1aV 1068G/V1068G ), impaired Arid1a-DNA interactions and resulted in both cardiac neural defects. Mutations in 4 different SWI/SNF subunits including ARID1A/B were identified in human congenital syndromes that include both neural and cardiac defects. Results: Here, we report ARID1A, which is a DNA-binding-subunit of the SWI/SNF epigenetic complex, controls both neurogenesis and cardiogenesis from human embryonic stem cells (hESCs) via employing distinct mechanisms. CRISPR/Cas-9 knockout of ARID1A (ARID1A -/- ) led to spontaneous differentiation of neural cells together with globally enhanced expression of neurogenic genes in undifferentiated hESCs. Additionally, when compared with WT hESCs, cardiac differentiation from ARID1A -/- hESCs was prominently suppressed, whereas neural differentiation was significantly promoted. Whole genome-wide ChIP-seq and ATAC-seq analyses revealed that ARID1A was required to open chromatin accessibility on promoters of essential cardiogenic genes, and temporally associated with key cardiogenic transcriptional factors T and MEF2C during early cardiac development. However, during neural development, transcription of most essential neurogenic genes was dependent on ARID1A and ARID1A could interact with REST, which is a known transcriptional repressor. Conclusions: We uncovered the key and opposite roles by ARID1A to govern both early human cardiac and neural development and characterized the mechanisms. We found global chromatin accessibility on cardiogenic genes was dependent on ARID1A, whereas transcriptional activity of neurogenic genes was regulated by ARID1A, possibly through ARID1A-REST interaction.

Background Early human heart and brain development simultaneously occur during embryogenesis. Notably, in human newborns, congenital heart defects strongly associate with neurodevelopmental abnormalities, suggesting a common gene or complex underlying both cardiogenesis and neurogenesis. However, due to lack of in vivo studies, the molecular mechanisms that govern both early human heart and brain development remain elusive. Results Here, we report ARID1A, a DNA-binding subunit of the SWI/SNF epigenetic complex, controls both neurogenesis and cardiogenesis from human embryonic stem cells (hESCs) through distinct mechanisms. Knockout-of-ARID1A (ARID1A−/−) leads to spontaneous differentiation of neural cells together with globally enhanced expression of neurogenic genes in undifferentiated hESCs. Additionally, when compared with WT hESCs, cardiac differentiation from ARID1A −/− hESCs is prominently suppressed, whereas neural differentiation is significantly promoted. Whole genome-wide scRNA-seq, ATAC-seq, and ChIP-seq analyses reveal that ARID1A is required to open chromatin accessibility on promoters of essential cardiogenic genes, and temporally associated with key cardiogenic transcriptional factors T and MEF2C during early cardiac development. However, during early neural development, transcription of most essential neurogenic genes is dependent on ARID1A, which can interact with a known neural restrictive silencer factor REST/NRSF. Conclusions We uncover the opposite roles by ARID1A to govern both early cardiac and neural development from pluripotent stem cells. Global chromatin accessibility on cardiogenic genes is dependent on ARID1A, whereas transcriptional activity of neurogenic genes is under control by ARID1A, possibly through ARID1A-REST/NRSF interaction.

Additional file 1. Fig. S1: Establishment of ARID1A null H9 hESC line. Fig. S2 ScRNAseq analysis of undifferentiated WT and ARID1A−/− hESCs. Fig. S3 Identity of neural cells from ARID1A−/− hESCs. Fig. S4 ScRNA-seq reveals loss-of-ARID1A represses cardiac but promotes neural differentiation from hESCs. Fig. S5 Functional enrichment analysis. Fig. S6 Loss-of-ARID1A promotes neural differentiation under neural differentiation conditions and knockdown of ARID1A promotes cardiac differentiation for hESCs. Fig. S7 ARID1A affects chromatin accessibility and interacts with other transcriptional factors.

Additional file 7. Review history.

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, with an estimated global prevalence of 1 in 4 individuals. Aberrant transcriptional control of gene expression is central to the pathophysiology of metabolic diseases. However, the molecular mechanisms leading to gene dysregulation are not well understood. Histone modifications play important roles in the control of transcription. Acetylation of histone 3 at lysine 9 (H3K9ac) is associated with transcriptional activity and is implicated in transcript elongation by controlling RNA polymerase II (RNAPII) pause-release. Hence, changes in this histone modification may shed information on novel pathways linking transcription control and metabolic dysfunction. Here, we carried out genome-wide analysis of H3K9ac in the liver of mice fed a control or a high-fat diet (an animal model of NAFLD), and asked whether this histone mark associates with changes in gene expression. We found that over 70% of RNAPII peaks in promoter-proximal regions overlapped with H3K9ac, consistent with a role of H3K9ac in the regulation of transcription. When comparing high-fat with control diet, approximately 17% of the differentially expressed genes were associated with changes in H3K9ac in their promoters, showing a strong correlation between changes in H3K9ac signal and gene expression. Overall, our data indicate that in response to a high-fat diet, dysregulated gene expression of a subset of genes may be attributable to changes in transcription elongation driven by H3K9ac. Our results point at an added mechanism of gene regulation that may be important in the development of metabolic diseases.

The problem of biological invasions attributed to ballast water release is an ongoing problem that threatens ecosystems and human health. Ultraviolet (UV) radiation has been increasingly used for ballast water treatment mainly due to the advantages of short contact time and minimized harmful disinfection by products. In this study, the impact of salinity on the inactivation of Vibrio cholerae (NCTC 7253) was examined, and comparison of inactivation level and disinfection kinetics after medium-pressure (MP) (1 kW) and low-pressure (LP) (10 W) UV irradiation was made. MP UV exposure resulted in higher inactivation efficacy against V. cholerae than LP UV exposure especially at lower UV doses (≤3 mJ cm−2) and salinity had a negative impact on both MP and LP UV disinfection, especially at higher UV doses (≥3 mJ cm−2 for MP and ≥4 mJ cm−2 for LP). To understand the mechanisms of salinity effect on V. cholerae, the enzyme-linked immunosorbent assay (ELISA) was employed to determine the number of cyclobutane pyrimidine dimers (CPDs), one major type of DNA damage. No significant effects of salinity were found at the CPDs level except for 3% artificial seawater after LP UV exposure case. It is imperative that site-specific conditions of salinity be taken into account in the design of UV reactors to treat V. cholerae and other species.

Three common virucidal techniques (chlorine, UV and UV/TiO2) were applied to inactivate virus (MS2 and Phi X174) in condensate water after the evaporation of source-separated urine for reclaimed water. The inactivation efficiencies were compared with the results of previous studies, with the emphasis on the analysis of water matrix effects. Results showed that all virus inactivation in condensate water were lower than the control (in sterilized DI water). As for UV/TiO2 disinfection, both nitrate and ammonia nitrogen could promote slightly viral inactivation, while the inhibition by urea was dominant. Similarly, ammonia nitrogen had greater impacts on chlorine disinfection than urea and nitrate. In contrast, all water matrices (urea, nitrate and ammonia nitrogen) had little influence on UV disinfection. Based on the findings in this study, UV disinfection could be recommended for disinfecting the reclaimed water from the evaporation of source-separated urine.

An experimental study is performed to investigate mechanisms of the interfacial behavior and their associated pressure oscillations in steam jet condensation in subcooled water flow in a vertical pipe. The transient interfacial behavior of the condensing jet is first captured by a high speed camera, and then its parameters are quantitatively computed by using digital image processing technology. Pressure oscillations associated with jet interfacial evolutions are acquired by flush mounted pressure transducers with high frequency response on the wall. The interfacial behavior of the jet at two typical condensation regimes, i.e., bubbling regime and jetting regime, and their corresponding quantitative temporal and spatial evolutions of radial and axial interfaces and pressure oscillations are analyzed. With increase of steam mass flux, interfacial oscillations and pressure oscillations reach local maximum near the sonic point, and they remain almost unchanged after entering the supersonic region. Dominant frequencies of radial and axial interfacial oscillations and those of pressure oscillations are almost the same at subsonic and sonic conditions, while the dominant frequency disappears at supersonic conditions. Very strong correlations between interfacial oscillations and pressure oscillations are quantified through the oscillation intensity and correlation coefficient and also the power spectrum density, which confirms quantitatively that pressure oscillations are induced by interfacial oscillations of the jet.

An experimental study is conducted to investigate interfacial characteristics of direct contact condensation of steam jet in counter-current subcooled water flow in confined conditions. A customized visualization window and a high-speed camera are combined together to capture and record the dynamical interface behavior of the condensing jet. The transient interface behavior of the jet is analyzed and discussed quantitatively by utilizing digital image processing technology. With increase of steam mass flux, the bubbling and jetting regime appear successively at subsonic conditions and sonic or supersonic conditions, respectively. The transient radial interface position along all axial locations downstream of the jet is obtained quantitatively for these two typical condensation regimes. The probability distribution function and power spectrum density of the radial interface position along all axial locations of a certain jet follow almost the same principles in the time-frequency domain. Significant variations of the probability distribution function and power spectrum density between the bubbling and jetting regimes happen at transonic condition. With increase of axial distance away from the nozzle exit, the probability of the pinch-off events first rise and then drops in subsonic and sonic conditions. While the jet interface is very stable and no pinch-off events occur in supersonic condition.

Gene expression in estrogen receptor (ER)-positive breast cancer cells is predominantly driven by ER-estradiol (E2) signaling. However, the effects of ER-E2 signaling on the overall chromatin architecture and accessibility to transcription regulators are not well understood. Chromatin architecture is a key determinant to gene expression patterns and therefore a comprehensive notation is essential for the interpretation of the ER cistrome. To investigate the effects of E2 signaling on chromatin architecture, we employed Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq), a high-throughput method to map chromatin accessibility via a hyperactive transposase that inserts sequencing tags into open regions. ATAC-seq was performed on MCF-7 cells, an ERα+ breast cancer cell line, treated with E2 or vehicle control for 1 or 3 hours. Results from the ATAC-seq were compared to RNA-seq data of 3-hours E2-treated MCF-7 cells to determine which regions of E2-regulated open or closed chromatin coincide with increased or decreased respective gene expression. Interestingly, we observed greater chromatin accessibility changes in genes repressed by E2 compared to genes induced by E2. Integration of ATAC-seq and RNA-seq data revealed distinct categories of E2-induced chromatin remodeling and downstream gene expression including increased chromatin accessibility, but repression of the corresponding gene, as well as decreased chromatin accessibility, but induction of the corresponding gene. Validation of the chromatin configurations predicted by ATAC-seq of select corresponding genes is currently being performed by ChIP-qPCR against specific histone modifications, such as H3K27Ac, a marker of open chromatin. To mechanistically dissect the distinct modes of E2 chromatin remodelling, we performed motif enrichment analysis of chromatin regions affected by E2. This analysis showed expected enrichment of estrogen response element (ERE), and pioneer factor FOXA1 and GATA3 response elements in E2-inducible genes with enhanced chromatin accessibility after E2-treatment. Regions in which the corresponding mRNA showed decreased transcript levels but displayed open chromatin in their promoter or enhancer region were enriched for the PBX3 motif and the ERE motif, respectively. Our results reveal previously unrecognized modes of E2-mediated restructuring of chromatin architecture and its correlation with transcription dynamics. This study provides grounds for future work to study fundamental relationships between chromatin accessibility and gene regulation in breast cancer under E2 and anti-estrogen treated conditions as well as in metastatic breast cancers with ERα mutations. Citation Format: Taylor M. Parker, Duojiao Chen, Poornima Bhat-Nakshatri, Xiaona Chu, Yunlong Liu, Yue Wang, Harikrishna Nakshatri. Non-linear relationship between estradiol-regulated changes in chromatin architecture and gene expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1006.

Three types of nanosilver materials, which were commercial, chemically-synthesized and biologically-synthesized, respectively, were compared in terms of the disinfection efficiencies against Escherichia coli and MS2 coliphage in order to pinpoint promising material with the best performance. Disinfection results showed biologically-synthesized silver nanoparticles (referred to hereafter as ‘bio-AgNPs’) had the best disinfection performance, 10 mg/L of which was able to inactivate all the E. coli in 1 min (>6 log removals) and achieved 4 log removals of MS2 coliphage. Bio-AgNPs were therefore selected for further study in terms of effects of the concentration and contact time as well as the impacts of environmental conditions on the viral inactivation. Given the viral inactivation profile of bio-AgNPs shown in this study, it could be concluded that viral inactivation by bio-AgNPs could be inhibited by total organic carbon (TOC) (10 mg/L as humic acid) and chloride ion (5 mg/L) to a large extent while Ca2+/Mg2+/ionic strength only had minor effects on the viral inactivation at high concentrations (188 mg/L as CaCO3 of hardness or 5.6 mM of ionic strength, respectively). This part of the study may help enlighten further mechanism studies on viral inactivation by nanosilver.

The transfer of invasive organisms by ballast-water discharge has become a growing concern. UV treatment has become an attractive ballast water treatment technology due to its effectiveness, no harmful disinfection byproducts and easiness to handle. Two robust algae strains Microcystis viridis and Tetraselmis suecica were selected as indicator organisms to determine efficiency of medium-pressure (MP) UV-treatment on ballast water. Inactivation and potential repair of these two algae strains following MP UV irradiation were assessed under various turbidity, total organic carbon (TOC) and salinity conditions. The investigated range of UV doses was from 25 to 500 mJ/cm2. For M. viridis, results indicated that disinfection efficiency was negatively correlated with all of these three factors at low doses (25–200 mJ/cm2). Photoreactivation and dark repair were promoted at high TOC levels (6–15 mg/L) with about 6–25% higher repair levels compared with those in distilled water, whereas no significant impacts were identified for turbidity and salinity on both of the photoreactivation and dark repair. For T. suecica, increased turbidity and TOC levels both hindered the performance of UV irradiation at high doses (200–500 mJ/cm2). Suppressive effects on photoreactivation and dark repair were consistently observed with changes of all of the three factors. In conclusion, generally these three factors resulted in repressive effects on UV disinfection efficiency, and TOC played a more significant role in the levels of reactivation than the other two. The responses of T. suecica to these three factors were more sensitive than M. viridis.

Ultraviolet (UV) irradiation is an emerging technique for drinking water disinfection due to effective removal of enteric pathogens without generation of disinfection by-products (DBPs). In order to overcome the drawback of UV irradiation the integration of UV disinfection with sequential disinfectant was proposed. Among all the possible combinations and sequences, a UV/H2O2-Cl2 integrated system has proven to be effective in many previous studies. In this study, a UV/H2O2 flow-through system followed by free chlorine was built and studied. MS-2 coliphage, as a model for a waterborne virus, were inactivated to evaluate the disinfection capacity. Assimilable organic carbon (AOC) tests and an Ames assay using Salmonella typhimurium TA98 and TA100 on such a proposed integrated system were also performed to determine re-growth potential of bacteria and genotoxicity, respectively. Briefly, such a proposed flow-through system was effective in removal of MS-2 coliphage and no genotoxic potential was detected according to the results; however, an increase of AOC may raise concerns of bacterial re-growth along the subsequent distribution system.

Cryptosporidium parvum is a waterborne coccidian protozoan parasite known to infect humans, resulting in an illness known as cryptosporidiosis. The widely used USEPA method 1622 to detect Cryptosporidium is time consuming, and unable to provide the information on oocysts viability and species. In order to develop a fast detection method for viable C. parvum oocysts, a 0.2 μm pore size hollow fiber membrane and 0.45 μm pore size disc membrane were used to filter tap water. Modified Immunomagnetic separation (IMS) purification was followed, and the IMS condition was optimized to shorten the purification time. Finally, fluorescence in situ hybridization (FISH) and FITC-conjugated monoclonal antibody (FMAb) staining were combined to detect viable oocysts, and results indicated that the viable oocysts detection by FISH/FMAb can be achieved in 20 min. The total viable oocysts detection time can be shortened to less than 1.5 h without affecting oocysts recovery.

UV disinfection is highly effective against most pathogens, with the exception of the adenoviruses (AD). To date, many studies have focused on low-pressure (LP) UV inactivation of AD, but little is known about the effect of medium-pressure (MP) UV inactivation of AD. Despite numerous studies of LP UV inactivation of AD, extreme variabilities in the LP UV dose requirements of AD had been observed because of differing experimental conditions used, such as the types of cell lines used for AD enumeration. This study therefore investigates the effect of three different host cell lines (PLC/PRF/5, human embryonic kidney 293 [HEK293], and XP17BE) on the LP and MP UV dose requirements of AD serotype 5 (AD5), AD40, and AD41 under similar experimental settings. Results showed that for 4-log inactivation of AD, LP UV and MP UV doses needed to be in the ranges of 123 to 182 mJ/cm 2 and 65 to 90 mJ/cm 2 , respectively, when HEK293 and PLC/PRF/5 cells were used for enumeration. The UV doses required for MP UV inactivation of AD were significantly lower than those required for LP UV inactivation ( P value < 0.05). When different cell lines were used for enumeration, UV dose requirements for AD differed. AD were portrayed to be most susceptible to UV (LP UV doses of 2 and MP UV doses of 2 for 4-log AD inactivation) when the XP17BE cells were used as the host cell. The use of different cell lines for AD enumeration affected LP UV dose results more significantly than MP UV dose results ( P value < 0.05). Cell line variability factors for LP UV disinfection (CL LP ) and MP UV disinfection (CL MP ) for AD5, AD40, and AD41 enumerated with HEK293, PLC/PRF/5, and XP17BE cells were in the ranges of 1.0 to 3.2 and 1.0 to 2.5, respectively.

To determine if body weight change is directly related to altered leptin and neuropeptide Y (NPY) gene expression, we assessed adipose tissue weight, percent body fat, leptin and NPY mRNA levels and serum leptin concentration in pigs at weights of 1, 20, 40, 60, and 90 kg. The results indicated that the weight of adipose tissues and the percent body fat of pigs significantly increased and correlated with body weight (BW) from 1 to 90 kg (p

Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 –19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l.

Ultraviolet (UV) light disinfection has increasingly been used as an alternative method to replace conventional chlorine disinfection as it has been found to be a more efficient disinfection method. As UV disinfection only damages the nucleic acids of the microorganisms to prevent replication, there is a possibility of microorganisms repairing the damage sites. As few studies have investigated the reactivation of microorganisms after exposure to medium-pressure UV disinfection, it is essential for reactivation related to medium-pressure UV disinfection to be studied as medium-pressure lamps are gaining in popularity. Besides, disinfection by-products (DBPs) produced by UV disinfection have been discovered recently and may serve as a carbon source in the finished water, resulting in regrowth of the bacteria. It is therefore important to know the regrowth potential of bacteria with the existence of DBPs. In this study, the repair and regrowth of Escherichia coli after UV disinfection were investigated. Results showed that E. coli underwent photo repair (up to 5 log under fluorescent light conditions) more significantly than dark repair (up to 0.8 log in terms of bacterial count increase). The repair was generally found to be higher at low doses. At the same UV dose, it seems medium-pressure UV irradiation is able to control the repair to a lesser extent. In addition, the bacterial regrowth potential was studied with the addition of DBPs typically found in UV processes, such as acetic acid and formaldehyde. The maximum increase in bacterial count was found to be 0.3 log. Generally, the level of regrowth was insignificant compared with the increase of bacterial count due to bacterial repair.