Aquatic Reservoirs Research Articles

Influence of land use and rainfall on the optical properties of dissolved organic matter in a key drinking water reservoir in China

The concentration, source and composition of dissolved organic matter (DOM) in aquatic ecosystems are associated with land use and hydrological connectivity between terrestrial and aquatic systems. However, direct evidence of the effects of rainfall and land use on the variability of DOM in aquatic ecosystems is very limited. In this study, chromophoric DOM (CDOM) absorption and fluorescence spectroscopy were used to elucidate how rainfall and land use affect the variability of CDOM in the watershed of Lake Tianmu, a key drinking water reservoir in the Yangtze River Delta. The mean values of the fluorescence intensity (Fmax) of parallel factor analysis-derived humic-like components (C1, C3, C6) and tryptophan-like components C5 were higher in the southeastern inflowing river mouths than those downstream of the lake outlet regions. The upstream tributaries were mainly dominated by humic-like materials, while the lake was mainly dominated by protein-like materials. The Fmax values of four humic-like components and two tryptophan-like components all increased significantly as the %woodland decreased, but %anthropogenic land use (%cropland+%urban construction area) increased. The Fmax of the humic-like components at the inflowing tributaries and the lake increased with increasing rainfall during storm events, and the value was especially pronounced at the inflowing river mouths. We concluded that land use and hydrological conditions play an important role in influencing the CDOM source and optical composition, and these findings provide insights for the understanding of aquatic ecosystem metabolism and reservoir water quality management.

Vibrio cholerae.

Vibrio cholerae is the bacterial pathogen responsible for the disease cholera, plaguing many developing nations and areas of poor sanitation, and causing about 2.9 million cases and ~95 000 deaths annually. It is transmitted through contaminated water and infects the host using two major virulence factors: the toxin-coregulated pilus (TCP) and cholera toxin (CT). TCP is important for colonization of the host gut mucosal layer where CT is released and passes through the gastroendothelial wall to cause watery diarrhea. Biofilm formation by V. cholerae provides protection and a means of transportation for the bacteria to colonize a wide range of environments such as humans and aquatic reservoirs. V. cholerae is used as a model organism to study virulence due to its high infectious dose, ease of genetic manipulation, and rapid replication time. It is also a model for studying chemical signaling such as cell-to-cell communication via quorum sensing and cyclic dinucleotide signaling.

Trace element accumulation in Salvinia natans from areas of various land use types

Salvinia natans meets many criteria for accumulative bioindicators and phytoremediation agents. However, the majority of studies on its bioaccumulation capacity were performed under controlled culture conditions. In the present study, Salvinia natans was investigated in a field study. Plant and water samples were collected from aquatic reservoirs located in areas with various dominant land uses (forested, agricultural, residential and industrial). Contents of 10 trace elements (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) and phytomass were measured to estimate the bioindication and phytoremediation potential of the species. Results showed that contents of trace elements in S. natans were high compared with other aquatic ferns (Azolla japonica, A. pinata) as well as free-floating vascular plants (e.g. Pistia stratiotes, Hydrocharis morsus-ranae, Lemna sp., Eichhornia crassipes). High bioaccumulation factors for Cu, Fe, Mn, Ni, Pb and Zn confirm accumulative abilities of the plant. Application of neural networks (SOFMs) confirmed that the species may be used in bioindication: the land use type determined the composition of substances carried into water reservoirs with runoff and trace elements accumulated in Salvinia tissues. Ferns in industrial areas had the highest content of Cd, Cu and Zn, while in residential areas plants showed the highest content of As, Co, Fe, Mn, Ni and Pb. Element contents in S. natans in forested areas were the lowest. High standing stocks of Cd, Mn and Ni indicated an important role of S. natans in the cycling of elements and potential use in their removal from aquatic ecosystems.

Tilapia (Oreochromis niloticus) as a Putative Reservoir Host for Survival and Transmission of Vibrio cholerae O1 Biotype El Tor in the Aquatic Environment.

Studies have reported the occurrence of Vibrio cholerae in fish but little is known about the interaction between fish and toxigenic V. cholerae as opposed to phytoplankton, which are well-established aquatic reservoirs for V. cholerae. The present study determined the role of tilapia (Oreochromis niloticus) as a reservoir host for survival and transmission of V. cholerae in aquatic environments. Three experiments were performed with one repetition each, where O. niloticus (∼2 g) kept in beakers were inoculated with four V. cholerae strains (5 × 107 cfu/mL). Firstly, infected tilapia were kept in stagnant water and fed live brine shrimp (Artemia salina) larvae daily. Secondly, infected tilapia were kept without feeding and water was changed every 24 h. Thirdly, infected tilapia were fed and water was renewed daily. Infected tilapia and non-infected controls were sacrificed on days 1, 2, 3, 7, and 14 post-inoculation and V. cholerae were enumerated in intestinal content and water. Another experiment assessed the transmission of V. cholerae from infected to non-infected tilapia. The study revealed that El Tor biotype V. cholerae O1 and V. cholerae non-O1 colonized tilapia intestines and persisted at stable concentrations during the second week of the experiment whereas the Classical biotype was undetectable after 1 week. In stagnant water with feeding, V. cholerae counts dropped to 105 cfu/ml in water and from 107 to 104 cfu/intestine in fish after 14 days. When water was renewed, counts in water decreased from 107 to 103 cfu/ml and intestinal counts went from 106 to 102 cfu/intestine regardless of feeding. All strains were transmitted from infected to naïve fish after 24 h of cohabitation. Tilapia like other fish may play an essential role in the survival and dissemination of V. cholerae O1 in aquatic environments, e.g., the seventh pandemic strains mostly. In this study, tilapia were exposed to high concentrations of V. cholerae to ensure initial uptake and follow-up studies with lower doses resembling natural concentrations of V. cholerae in the aquatic environment are needed to confirm our findings.

Metabolic Pathway Analysis of Nitrogen and Phosphorus Uptake by the Consortium between C. vulgaris and P. aeruginosa.

Anthropogenic activities have increased the amount of urban wastewater discharged into natural aquatic reservoirs containing a high amount of nutrients such as phosphorus (Pi and PO), nitrogen (NH and NO) and organic contaminants. Most of the urban wastewater in Mexico do not receive any treatment to remove nutrients. Several studies have reported that an alternative to reduce those contaminants is using consortiums of microalgae and endogenous bacteria. In this research, a genome-scale biochemical reaction network is reconstructed for the co-culture between the microalga Chlorella vulgaris and the bacterium Pseudomonas aeruginosa. Metabolic Pathway Analysis (MPA), is applied to understand the metabolic capabilities of the co-culture and to elucidate the best conditions in removing nutrients. Theoretical yields for phosphorus removal under photoheterotrophic conditions are calculated, determining their values as 0.042 mmol of PO per g DW of C. vulgaris, 19.43 mmol of phosphorus (Pi) per g DW of C. vulgaris and 4.90 mmol of phosphorus (Pi) per g DW of P. aeruginosa. Similarly, according to the genome-scale biochemical reaction network the theoretical yields for nitrogen removal are 10.3 mmol of NH per g DW of P. aeruginosa and 7.19 mmol of NO per g DW of C. vulgaris. Thus, this research proves the metabolic capacity of these microorganisms in removing nutrients and their theoretical yields are calculated.

Definition of a Family of Nonmobile Colistin Resistance (NMCR-1) Determinants Suggests Aquatic Reservoirs for MCR-4.

Polymyxins, a family of cationic antimicrobial peptides, are recognized as a last‐resort clinical option used in the treatment of lethal infections with carbapenem‐resistant pathogens. A growing body of mobile colistin resistance (MCR) determinants renders colistin ineffective in the clinical and human sectors, posing a challenge to human health and food security. However, the origin and reservoir of the MCR family enzymes is poorly understood. Herein, a new family of nonmobile colistin resistance (from nmcr‐1 to nmcr‐1.8) from the aquatic bacterium Shewanella is reported. NMCR‐1 (541aa) displays 62.78% identity to MCR‐4. Genetic and structural analyses reveal that NMCR‐1 shares a similar catalytic mechanism and functional motifs, both of which are required for MCR action and its resultant phenotypic resistance to polymyxin. Phylogeny and domain‐swapping demonstrate that NMCR‐1 is a progenitor of MCR‐4 rather than MCR‐1/2. Additionally, the experiment of bacterial growth and viability reveals that NMCR‐1 promotes fitness cost as MCR‐1/4 does in the recipient Escherichia coli. In summary, the finding suggests that the aquatic bacterium Shewanella (and even its associated aquaculture) is a reservoir for MCR‐4 mobile colistin resistance.

Niche adaptation limits bacteriophage predation of Vibrio cholerae in a nutrient-poor aquatic environment

Vibrio cholerae, the causative agent of cholera, has reservoirs in fresh and brackish water where it interacts with virulent bacteriophages. Phages are the most abundant biological entity on earth and coevolve with bacteria. It was reported that concentrations of phage and V. cholerae inversely correlate in aquatic reservoirs and in the human small intestine, and therefore that phages may quench cholera outbreaks. Although there is strong evidence for phage predation in cholera patients, evidence is lacking for phage predation of V. cholerae in aquatic environments. Here, we used three virulent phages, ICP1, ICP2, and ICP3, commonly shed by cholera patients in Bangladesh, as models to understand the predation dynamics in microcosms simulating aquatic environments. None of the phages were capable of predation in fresh water, and only ICP1 was able to prey on V. cholerae in estuarine water due to a requirement for salt. We conclude that ICP2 and ICP3 are better adapted for predation in a nutrient rich environment. Our results point to the evolution of niche-specific predation by V. cholerae-specific virulent phages, which complicates their use in predicting or monitoring cholera outbreaks as well as their potential use in reducing aquatic reservoirs of V. cholerae in endemic areas.

Isolation and Characterization of Flavobacteriaceae from Farmed and Wild Nile Tilapia in Tanzania.

The present study was conducted to explore the occurrence of Flavobacteriaceae in wild Nile Tilapia Oreochromis niloticus (n=108) collected from Lake Victoria and farmed Nile Tilapia (n=187) collected from 12 ponds in the Morogoro region of Tanzania. The size of the ponds surveyed ranged from 130 to 150m2 . Pond parameters and fish morphometric data were recorded during sampling. In total, 67 Flavobacterium-like isolates (n=44 from farmed fish; n=23 from wild fish) were identified on the basis of colony morphology and biochemical tests. Sequences from the 16S ribosomal RNA (rRNA) gene revealed that all 67 isolates belonged to the genera Flavobacterium and Chryseobacterium. Based on 16S rRNA nucleotide identity, 26 isolates showed high similarity with C. indologenes (99-100% identity), 16 showed similarity to C. joostei (98-99.9%), and 17 were similar to diverse species of Chryseobacterium (97-99%). Three isolates were similar to F. aquatile and three were similar to F. indicum, with 99-100% nucleotide identity in both cases, and two isolates were similar to F. oryzae (99-100% identity). The findings obtained in this study provide a baseline for future studies and contribute to an understanding of the threats presented by the aquatic Flavobacteriaceae reservoir toward the development of healthy fish farming in Tanzania. Such knowledge is vital for the development of a sustainable aquaculture industry in Tanzania that will contribute to increased food security.

Lepenski Vir chronology and stratigraphy revisited

This article offers a new look at the stratigraphy and chronology of Mesolithic and Neolithic deposits at Lepenski Vir, particularly based on newly available Accelerator Mass Spectrometry (AMS) dating and aDNA genomic evidence. It focuses on a detailed analysis of several key contexts for which new radiocarbon dates are available while at the same time reviewing taphonomic and age-offset problems when dating human remains and other materials affected by the aquatic reservoir effect in the Danube Gorges area. The robust chronological evidence as well as available stratigraphic data overwhelmingly show that the start of the main and iconic phase of the occupation of this site, represented by the architecture of trapezoidal buildings and sculpted sandstone boulders, should unequivocally be dated to the period of the Mesolithic-Neolithic transition in the last two centuries of the seventh millennium cal BC. At this time, local forager populations of distinct hunter-gatherer genetic ancestry came into contact and mixed with incoming Neolithic, farming populations of north-western Anatolian genetic ancestry, based on the available genomic data but also supported by studies of material culture traditions. The article deals directly with the recent criticism of this chrono-stratigraphic model for Lepenski Vir.

Serologic and Virologic Evidence of Influenza A Viruses in Wild Boars ( Sus scrofa) from Two Different Locations in Italy.

Swine influenza viruses (SIVs) have been repeatedly demonstrated to circulate in wild boar ( Sus scrofa) populations, whereas no evidence of exposure to avian influenza viruses (AIVs) has been described in wild boar. To better understand how different environments may influence the ecology of influenza A viruses (IAVs) in wild suid populations, we examined biologic samples of wild boars from two study areas represented by an upland (UL) and a wetland (WL) in northern and central Italy, respectively. Serum samples were collected from 388 wild boars sampled in the UL, whereas both a serum sample and a nasal swab were obtained from each of 35 wild boars sampled in the WL. Twenty of 388 (5.2%) sera from the UL were positive by enzyme-linked immunosorbent assay for the presence of antibodies against influenza A nucleoprotein and some of these samples showed antibodies by hemagglutination inhibition to SIVs of H1N1 (1/20), H1N2 (10/20), and H3N2 (1/20) antigenic subtypes. No IAV-seropositive wild boar was detected in the WL, although one of 35 animals was found to be IAV-positive by both a reverse transcriptase PCR and a real-time reverse transcriptase PCR. We hypothesize an SIV exposure for IAV-seropositive wild boars occupying the UL, whereas a possible AIV spillover from aquatic bird species-natural reservoirs of IAVs-to wild boars in the WL cannot be ruled out. Further research is needed to better understand the role played by wild boars in IAV ecology in Mediterranean habitats.

Quorum Sensing Autoinducer(s) and Flagellum Independently Mediate EPS Signaling in Vibrio cholerae Through LuxO-Independent Mechanism.

Vibrio cholerae, the Gram-negative bacterium causing lethal diarrheal disease cholera, forms biofilm on solid surfaces to gain adaptive advantage for successful survival in aquatic reservoirs. Expression of exopolysaccharide (EPS), an extracellular matrix material, has been found critical for biofilm-based environmental persistence. In a subset of epidemic-causing V. cholerae, absence of flagellum but not motility was identified to induce elevated exopolysaccharide expression. Identification of the role played by quorum sensing autoinducer molecules, i.e., cholera autoinducer 1 (CAI-1) and autoinducer 2 (AI-2) as well as central regulator LuxO on EPS expression in the subset was explored. Deletion mutations were introduced in vital genes responsible for synthesizing CAI-1 (cqsA), AI-2 (luxS), flagellum (flaA), LuxO (luxO), flagellar motor (motX), and VpsR (vpsR) in the model strain MO10. Subsequent phenotypic alterations in terms of colony morphology, EPS expression, biofilm formation, and transcription level of relevant genes were analyzed. Autoinducer cross-feeding experiment confirmed the role of autoinducers in EPS signaling. Results reveal that autoinducers and flagellum are the two major EPS signaling units in this subset where one unit becomes predominant for EPS production in absence of the other. Moreover, either unit exerts negative influence on EPS induction by the other. Both the EPS signaling cascades are independent of LuxO contribution and essentially involve sodium-driven flagellar motor and VpsR. A cell density and flagellum-mediated, but LuxO-independent, EPS signaling mechanism is considered to be functional in these organisms that confers their survival fitness.

Mathematical assessment of the role of environmental factors on the dynamical transmission of cholera

In this paper, we investigate the impact of environmental factors on the dynamical transmission of cholera within a human community. We propose a mathematical model for the dynamical transmission of cholera that incorporates the virulence of bacteria and the commensalism relationship between bacteria and the aquatic reservoirs on the persistence of the disease. We provide a theoretical study of the model. We derive the basic reproduction number R0 which determines the extinction and the persistence of the infection. We show that the disease-free equilibrium is globally asymptotically stable whenever R0≤1, while when R0>1, the disease-free equilibrium is unstable and there exists a unique endemic equilibrium point which is locally asymptotically stable on a positively invariant region of the positive orthant. The sensitivity analysis of the model has been performed in order to determine the impact of related parameters on outbreak severity. Theoretical results are supported by numerical simulations, which further suggest the necessity to implement sanitation campaigns of aquatic environments by using suitable products against the bacteria during the periods of growth of aquatic reservoirs.

Sulfidic Anion Concentrations on Early Earth for Surficial Origins-of-Life Chemistry

A key challenge in origin-of-life studies is understanding the environmental conditions on early Earth under which abiogenesis occurred. While some constraints do exist (e.g., zircon evidence for surface liquid water), relatively few constraints exist on the abundances of trace chemical species, which are relevant to assessing the plausibility and guiding the development of postulated prebiotic chemical pathways which depend on these species. In this work, we combine literature photochemistry models with simple equilibrium chemistry calculations to place constraints on the plausible range of concentrations of sulfidic anions (HS−, HSO3−, SO32−) available in surficial aquatic reservoirs on early Earth due to outgassing of SO2 and H2S and their dissolution into small shallow surface water reservoirs like lakes. We find that this mechanism could have supplied prebiotically relevant levels of SO2-derived anions, but not H2S-derived anions. Radiative transfer modeling suggests UV light would have remained abundant on the planet surface for all but the largest volcanic explosions. We apply our results to the case study of the proposed prebiotic reaction network of Patel et al. (2015) and discuss the implications for improving its prebiotic plausibility. In general, epochs of moderately high volcanism could have been especially conducive to cyanosulfidic prebiotic chemistry. Our work can be similarly applied to assess and improve the prebiotic plausibility of other postulated surficial prebiotic chemistries that are sensitive to sulfidic anions, and our methods adapted to study other atmospherically derived trace species.

Potential effects of mechanically removing macrophytes on the phytoplankton community of a subtropical reservoir

ABSTRACT Intensive growth of aquatic macrophytes interferes with water quality and ecosystem dynamics worldwide. Although mechanically removing macrophytes is the most commonly used method for their eradication, it can also cause undesirable disturbances in aquatic reservoir communities. We performed laboratory incubations of phytoplankton sampled before and after macrophytes were mechanically removed from the Piraquara II reservoir, South Brazil. We analyzed changes in growth and composition of the main phytoplankton groups with respect to nutrient shifting. Prior to removing the macrophytes, the phytoplankton community was dominated by low cell abundances of diatoms and flagellates. In contrast, growth rates of cyanobacteria (mainly Cylindrospermopsis raciborskii, Pseudanabaena sp., and Geitlerinema sp.) and of colonial chlorophytes were favored after macrophyte removal, while the abundances of diatoms and flagellates decreased. Our results suggest that removing macrophytes causes dramatic changes in phytoplankton composition and biomass and selects for toxigenic species of cyanobacteria. These changes were probably associated with the disturbance caused by removing the macrophytes, which immediately created new environmental conditions prone to species competition. These findings indicate that the use of mechanical techniques to manage macrophytes should be carefully considered, along with monitoring of harmful species and changes of limnological parameters.

Combined influence of meteorological, hydrological, and physicochemical factors on macrophyte overgrowth in agricultural reservoirs

Maintaining moderate levels of aquatic plant cover in agricultural reservoirs is an important issue because aquatic plant development is closely related to diverse ecosystem functions, including the regulation of the microconditions of the air–water environment, the production of food sources, and the structuring of physical habitats. We analyzed annual changes in aquatic plant cover in the Junam reservoirs using remote sensing images and field-survey data. We established a time series of aquatic plant cover using satellite images, aerial photography, and field-survey data from 1997 to 2016. We assessed the relationship between aquatic plant cover and reservoir environmental conditions. No monotonic trend in aquatic plant cover was observed during the 20-year study period. However, we found that the total aquatic plant cover was influenced by a complex combination of meteorological (winter temperature and wind speed), hydrological (water level), and physicochemical (conductivity, N:P ratio) factors for the reservoir. We further suggest a collective management scheme focused on nutrient and water-level conditions to control the overgrowth of aquatic plants in agricultural reservoirs.

Environmental Surveillance of Zoonotic Francisella tularensis in the Netherlands.

Tularemia is an emerging zoonosis caused by the Gram-negative bacterium Francisella tularensis, which is able to infect a range of animal species and humans. Human infections occur through contact with animals, ingestion of food, insect bites or exposure to aerosols or water, and may lead to serious disease. F. tularensis may persist in aquatic reservoirs. In the Netherland, no human tularemia cases were notified for over 60 years until in 2011 an endemic patient was diagnosed, followed by 17 cases in the 6 years since. The re-emergence of tularemia could be caused by changes in reservoirs or transmission routes. We performed environmental surveillance of F. tularensis in surface waters in the Netherlands by using two approaches. Firstly, 339 samples were obtained from routine monitoring -not related to tularemia- at 127 locations that were visited between 1 and 8 times in 2015 and 2016. Secondly, sampling efforts were performed after reported tularemia cases (n = 8) among hares or humans in the period 2013–2017. F. tularensis DNA was detected at 17% of randomly selected surface water locations from different parts of the country. At most of these positive locations, DNA was not detected at each time point and levels were very low, but at two locations contamination was clearly higher. From 7 out of the 8 investigated tularemia cases, F. tularensis DNA was detected in at least one surface water sample collected after the case. By using a protocol tailored for amplification of low amounts of environmental DNA, 10 gene targets were sequenced. Presence of F. tularensis subspecies holarctica was confirmed in 4 samples, and in 2 of these, clades B.12 and B.6 were identified. This study shows that for tularemia, information regarding the spatial and temporal distribution of its causative agent could be derived from environmental surveillance of surface waters. Tracking a particular strain in the environment as source of infection is feasible and could be substantiated by genotyping, which was achieved in water samples with only low levels of F. tularemia present. These techniques allow the establishment of a link between tularemia cases and environmental samples without the need for cultivation.

Theoretical Assessment of the Impact of Climatic Factors in a Vibrio Cholerae Model.

A mathematical model for Vibrio Cholerae (V. Cholerae) in a closed environment is considered, with the aim of investigating the impact of climatic factors which exerts a direct influence on the bacterial metabolism and on the bacterial reservoir capacity. We first propose a V. Cholerae mathematical model in a closed environment. A sensitivity analysis using the eFast method was performed to show the most important parameters of the model. After, we extend this V. cholerae model by taking account climatic factors that influence the bacterial reservoir capacity. We present the theoretical analysis of the model. More precisely, we compute equilibria and study their stabilities. The stability of equilibria was investigated using the theory of periodic cooperative systems with a concave nonlinearity. Theoretical results are supported by numerical simulations which further suggest the necessity to implement sanitation campaigns of aquatic environments by using suitable products against the bacteria during the periods of growth of aquatic reservoirs.

Transcriptional and Post‐Transcriptional Regulation of mtlA in Vibrio cholerae

Vibrio cholerae, the bacterium that causes cholera, performs a complex regulation of genes encoding carbon‐source transporters in order to survive in both aquatic reservoirs and the human small intestine. One such transporter is MtlA, which operates within the phosphotransferase system (PTS), a highly‐conserved system for carbohydrate uptake across bacteria. MtlA concomitantly phosphorylates and transports mannitol, the six‐carbon sugar alcohol produced by algae, into the cell. In addition to mtlA, the mtl locus contains mtlS and mtlR, which encode two major regulators of MtlA. mtlS encodes a 120‐nucleotide small regulatory RNA (sRNA) that posttranscriptionally regulates MtlA synthesis by binding to the mtlA mRNA 5′ untranslated region. Our objective is to identify regulators of mtlS expression. We have constructed a V. cholerae strain harboring a chromosomal mtlS‐lacZ transcriptional fusion. Using a V. cholerae genomic library, we identified putative regulators of mtlS expression. The second regulator of mtlA, encoded by mtlR, showed repressive effects in Escherichia coli, but had not been well characterized in V. cholerae. We studied how MtlR regulates MtlA activity in V. cholerae grown in a variety of carbon sources. Biofilm assays demonstrated that mtlR overexpression results in a greater than 50% decrease in biofilm formation (p<0.001 by unpaired two‐tailed t‐test), an activity known to be positively affected by MtlA. qRT‐PCR showed that a ΔmtlR mutant has higher mtlA RNA levels than a wild‐type control when grown in glucose‐supplemented minimal medium (p<0.0001 by unpaired two‐tailed t‐test), and even higher mtlA RNA levels when grown in maltose‐ and mannose‐ supplemented minimal medium (p<0.01 by unpaired two‐tailed t‐test). Western blotting analysis reflected these increases; MtlA protein levels were more elevated in ΔmtlR compared to wild‐type when grown in glucose, maltose, and mannose. The ΔmtlR mutant was partially complemented, as demonstrated by qRT‐PCR (p<0.01 by unpaired two‐tailed ttest) and western blotting analysis. This shows that the observed increases in MtlA were a direct effect of the gene product of mtlR. These results contribute to a model in which MtlR acts as a transcriptional repressor of mtlA in non‐mannitol conditions, working synergistically with MtlS to regulate mtlA.Support or Funding InformationNIH R15 AI090606This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cyclic di-GMP Regulates TfoY in Vibrio cholerae To Control Motility by both Transcriptional and Posttranscriptional Mechanisms.

3',5'-Cyclic diguanylic acid (c-di-GMP) is a bacterial second messenger molecule that is a key global regulator in Vibrio cholerae, but the molecular mechanisms by which this molecule regulates downstream phenotypes have not been fully characterized. One such regulatory factor that may respond to c-di-GMP is the Vc2 c-di-GMP-binding riboswitch that is hypothesized to control the expression of the downstream putative transcription factor TfoY. Although much is known about the physical and structural properties of the Vc2 riboswitch aptamer, the nature of its expression and function in V. cholerae has not been investigated. Here, we show that Vc2 functions as an off switch to inhibit TfoY production at intermediate and high concentrations of c-di-GMP. At low c-di-GMP concentrations, TfoY production is induced to stimulate dispersive motility. We also observed increased transcription of tfoY at high intracellular concentrations of c-di-GMP, but this induction is independent of the Vc2 riboswitch and occurs via transcriptional control of promoters upstream of tfoY by the previously identified c-di-GMP dependent transcription factor VpsR. Our results show that TfoY is induced by c-di-GMP at both low and high intracellular concentrations of c-di-GMP via posttranscriptional and transcriptional mechanisms, respectively. This regulation contributes to the formation of three distinct c-di-GMP signaling states in V. choleraeIMPORTANCE The bacterial pathogen Vibrio cholerae must transition between life in aquatic environmental reservoirs and life in the gastrointestinal tract. Biofilm formation and bacterial motility, and their control by the second messenger molecule c-di-GMP, play integral roles in this adaptation. Here, we define the third major mechanism by which c-di-GMP controls bacterial motility. This pathway utilizes a noncoding RNA element known as a riboswitch that, when bound to c-di-GMP, inhibits the expression of the transcription factor TfoY. TfoY production switches V. cholerae motility from a dense to a dispersive state. Our results suggest that the c-di-GMP signaling network of V. cholerae can exist in at least three distinct states to regulate biofilm formation and motility.

Elevated nitrate alters the metabolic activity of embryonic zebrafish.

Nitrate accumulation in aquatic reservoirs from agricultural pollution has often been overlooked as a water quality hazard, yet a growing body of literature suggests negative effects on human and wildlife health following nitrate exposure. This research seeks to understand differences in oxygen consumption rates between different routes of laboratory nitrate exposure, whether via immersion or injection, in zebrafish (Danio rerio) embryos. Embryos were exposed within 1 h post fertilization (hpf) to 0, 10, and 100 mg/L NO3-N with sodium nitrate, or to counter ion control (CIC) treatments using sodium chloride. Embryos in the immersion treatments received an injection of 4 nL of appropriate treatment solution into the perivitelline space. At 24 hpf, Oxygen Consumption Rates (OCR) were measured and recorded invivo using the Agilent Technologies XFe96 Extracellular Flux Analyzer and Spheroid Microplate. Immersion exposures did not induce significant changes in OCR, yet nitrate induced significant changes when injected through the embryo chorion. Injection of 10 and 100 mg/L NO3-N down-regulated OCR compared to the control treatment group. Injection of the 100 mg/L CIC also significantly down-regulated OCR compared to the control treatment group. Interestingly, the 100 mg/L NO3-N treatment further down-regulated OCR compared to the 100 mg/L CIC treatment, suggesting the potential for additive effects between the counter ion and the ion of interest. These data support that elevated nitrate exposure can alter normal metabolic activity by changing OCR in 24 hpf embryos. These results highlight the need for regularly examining the counter ion of laboratory nitrate compounds while conducting research with developing zebrafish, and justify examining different routes of laboratory nitrate exposure, as the chorion may act as an effective barrier to nitrate penetration in zebrafish, which may lead to conservative estimates of significant effects in other species for which nitrate more readily penetrates the chorion.