13 research outputs found
Exogenous indirect photoinactivation of bacterial pathogens and indicators in water with natural and synthetic photosensitizers in simulated sunlight with reduced UVB
ABSTRACT Aims: To investigate the UVB-independent and exogenous indirect photoinactivation of eight human health-relevant bacterial species in the presence of photosensitizers. Methods and Results: Eight bacterial species were exposed to simulated sunlight with greatly reduced UVB light intensity in the presence of three synthetic photosensitizers and two natural photosensitizers. Inactivation curves were fit with shoulder-log linear or first order kinetic models, from which the presence of a shoulder and magnitude of inactivation rate constants were compared. 84% reduction in the UVB light intensity roughly matched a 72-95% reduction in the overall bacterial photoinactivation rate constants in sensitizer-free water. With the UVB light mostly reduced, the exogenous indirect mechanism contribution was evident for most bacteria and photosensitizers tested, although most prominently with the Gram-positive bacteria. Conclusions: Results confirm the importance of UVB light in bacterial photoinactivation and, with the reduction of the UVB light intensity, that the Gram-positive bacteria are more vulnerable to the exogenous indirect mechanism than Gram-negative bacteria. Significance and Impact of Study: UVB is the most important range of the sunlight spectrum for bacterial photoinactivation. In aquatic environments where photosensitizers are present and there is high UVB light attenuation, UVA and visible wavelengths can contribute to exogenous indirect photoinactivation
Photoinactivation of Eight Health-Relevant Bacterial Species: Determining the Importance of the Exogenous Indirect Mechanism
It is presently unknown
to what extent the endogenous direct, endogenous
indirect, and exogenous indirect mechanisms contribute to bacterial
photoinactivation in natural surface waters. In this study, we investigated
the importance of the exogenous indirect mechanism by conducting photoinactivation
experiments with eight health-relevant bacterial species (<i>Bacteroides thetaiotaomicron, Campylobacter jejuni</i>, <i>Enterococcus faecalis</i>, <i>Escherichia coli</i> K12, <i>E. coli</i> O157:H7, <i>Salmonella enterica</i> serovar Typhimurium LT2, <i>Staphylococcus aureus</i>,
and <i>Streptococcus bovis</i>). We used three synthetic
photosensitizers (methylene blue, rose bengal, and nitrite) and two
model natural photosensitizers (Suwannee River natural organic matter
and dissolved organic matter isolated from a wastewater treatment
wetland) that generated singlet oxygen and hydroxyl radical. <i>B. thetaiotaomicron</i> had larger first order rate constants
than all other organisms under all conditions tested. The presence
of the synthetic photosensitizers generally enhanced photoinactivation
of Gram-positive facultative anaerobes (<i>Ent. faecalis</i>, <i>Staph. aureus</i>, and <i>Strep. bovis</i>). Among Gram-negative bacteria, only methylene blue with <i>E. coli</i> K12 and rose bengal with <i>C. jejuni</i> showed an enhancing effect. The presence of model natural photosensitizers
either reduced or did not affect photoinactivation rate constants.
Our findings highlight the importance of the cellular membrane and
photosensitizer properties in modulating the contribution of the exogenous
indirect mechanism to the overall bacterial photoinactivation
Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches.
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems
The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
We present observations and timing analyses of 68 millisecond pulsars (MSPs)
comprising the 15-year data set of the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA)
experiment that is sensitive to low-frequency gravitational waves. This is
NANOGrav's fifth public data release, including both "narrowband" and
"wideband" time-of-arrival (TOA) measurements and corresponding pulsar timing
models. We have added 21 MSPs and extended our timing baselines by three years,
now spanning nearly 16 years for some of our sources. The data were collected
using the Arecibo Observatory, the Green Bank Telescope, and the Very Large
Array between frequencies of 327 MHz and 3 GHz, with most sources observed
approximately monthly. A number of notable methodological and procedural
changes were made compared to our previous data sets. These improve the overall
quality of the TOA data set and are part of the transition to new pulsar timing
and PTA analysis software packages. For the first time, our data products are
accompanied by a full suite of software to reproduce data reduction, analysis,
and results. Our timing models include a variety of newly detected astrometric
and binary pulsar parameters, including several significant improvements to
pulsar mass constraints. We find that the time series of 23 pulsars contain
detectable levels of red noise, 10 of which are new measurements. In this data
set, we find evidence for a stochastic gravitational-wave background.Comment: 90 pages, 74 figures, 6 tables; published in Astrophysical Journal
Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational
Wave Background. For questions or comments, please email
[email protected]
Conducting Nanosponge Electroporation for Affordable and High-Efficiency Disinfection of Bacteria and Viruses in Water
High-efficiency,
affordable, and low energy water disinfection methods are in great
need to prevent diarrheal illness, which is one of the top five leading
causes of death over the world. Traditional water disinfection methods
have drawbacks including carcinogenic disinfection byproducts formation,
energy and time intensiveness, and pathogen recovery. Here, we report
an innovative method that achieves high-efficiency water disinfection
by introducing nanomaterial-assisted electroporation implemented by
a conducting nanosponge filtration device. The use of one-dimensional
(1D) nanomaterials allows electroporation to occur at only several
volts, which is 2 to 3 orders of magnitude lower than that in traditional
electroporation applications. The disinfection mechanism of electroporation
prevents harmful byproduct formation and ensures a fast treatment
speed of 15 000 L/(h·m<sup>2</sup>), which is equal to
a contact time of 1 s. The conducting nanosponge made from low-cost
polyurethane sponge coated with carbon nanotubes and silver nanowires
ensures the device’s affordability. This method achieves more
than 6 log (99.9999%) removal of four model bacteria, including <i>Escherichia coli</i>, <i>Salmonella enterica</i> Typhimirium, <i>Enterococcus faecalis</i>, and <i>Bacillus subtilis</i>, and more than 2 log (99%) removal of one model virus, bacteriophage
MS2, with a low energy consumption of only 100 J/L
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Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches.
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems
Solar Inactivation of Enterococci and <i>Escherichia coli</i> in Natural Waters: Effects of Water Absorbance and Depth
The decay of sewage-sourced <i>Escherichia coli</i> and
enterococci was measured at multiple depths in a freshwater marsh,
a brackish water lagoon, and a marine site, all located in California.
The marine site had very clear water, while the waters from the marsh
and lagoon contained colored dissolved organic matter that not only
blocked light but also produced reactive oxygen species. First order
decay rate constants of both enterococci and <i>E. coli</i> were between 1 and 2 d<sup>–1</sup> under low light conditions
and as high as 6 d<sup>–1</sup> under high light conditions.
First order decay rate constants were well correlated to the daily
average UVB light intensity corrected for light screening incorporating
water absorbance and depth, suggesting endogenous photoinactivation
is a major pathway for bacterial decay. Additional laboratory experiments
demonstrated the presence of colored dissolved organic matter in marsh
water enhanced photoinactivation of a laboratory strain of <i>Enterococcus faecalis</i>, but depressed photoinactivation of
sewage-sourced enterococci and <i>E. coli</i> after correcting
for UVB light screening, suggesting that although the exogenous indirect
photoinactivation mechanism may be active against <i>Ent. faecalis,</i> it is not for the sewage-source organisms. A simple linear regression
model based on UVB light intensity appears to be a useful tool for
predicting inactivation rate constants in natural waters of any depth
and absorbance
Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280–320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.ISSN:2050-7887ISSN:2050-789
Diurnal Variation in Enterococcus Species Composition in Polluted Ocean Water and a Potential Role for the Enterococcal Carotenoid in Protection against Photoinactivation
Enterococcus species composition was determined each hour for 72 h at a polluted marine beach in Avalon, Santa Catalina Island, CA. Species composition during the day was significantly different from that at night, based on an analysis of similarity. Enterococcus faecium and E. faecalis were more prevalent at night than during the day, while E. hirae and other Enterococcus species were more prevalent during the day than the night. Enterococcus spp. containing a yellow pigment were more common during the day than the night, suggesting that the pigmented phenotype may offer a competitive advantage under sunlit conditions. A laboratory microcosm experiment established that the pigmented E. casseliflavus isolate and a pigmented E. faecalis isolate recovered from the field site decay slower than a nonpigmented E. faecalis isolate in a solar simulator in simulated, clear seawater. This further supports the idea that the yellow carotenoid pigment in Enterococcus provides protection under sunlit conditions. The findings are in accordance with previous work with other carotenoid-containing nonphotosynthetic and photosynthetic bacteria that suggests that the carotenoid is able to quench reactive oxygen species capable of causing photoinactivation and photostress. The results suggest that using enterococcal species composition as a microbial source tracking tool may be hindered by the differential environmental persistence of pigmented and nonpigmented enterococci
Rapid water disinfection using vertically aligned MoS2 nanofilms and visible light
Solar energy is readily available in most climates and can be used for water purification. However, solar disinfection of drinking water mostly relies on ultraviolet light, which represents only 4% of the total solar energy, and this leads to a slow treatment speed. Therefore, the development of new materials that can harvest visible light for water disinfection, and so speed up solar water purification, is highly desirable. Here we show that few-layered vertically aligned MoS2 (FLV-MoS2) films can be used to harvest the whole spectrum of visible light (???50% of solar energy) and achieve highly efficient water disinfection. The bandgap of MoS2 was increased from 1.3 to 1.55 eV by decreasing the domain size, which allowed the FLV-MoS2 to generate reactive oxygen species (ROS) for bacterial inactivation in the water. The FLV-MoS2 showed a ???15 times better log inactivation efficiency of the indicator bacteria compared with that of bulk MoS2, and a much faster inactivation of bacteria under both visible light and sunlight illumination compared with the widely used TiO2. Moreover, by using a 5 nm copper film on top of the FLV-MoS2 as a catalyst to facilitate electron–hole pair separation and promote the generation of ROS, the disinfection rate was increased a further sixfold. With our approach, we achieved water disinfection of >99.999% inactivation of bacteria in 20 min with a small amount of material (1.6 mg l–1) under simulated visible light.close