Population Of Vegetative Cells Research Articles

In Silico Design of Potential Small-Molecule Antibiotic Adjuvants against Salmonella typhimurium Ortho Acetyl Sulphydrylase Synthase to Address Antimicrobial Resistance.

The inhibition of O-acetyl sulphydrylase synthase isoforms has been reported to represent a promising approach for the development of antibiotic adjuvants. This occurs via the organism developing an unpaired oxidative stress response, causing a reduction in antibiotic resistance in vegetative and swarm cell populations. This consequently increases the effectiveness of conventional antibiotics at lower doses. This study aimed to predict potential inhibitors of Salmonella typhimurium ortho acetyl sulphydrylase synthase (StOASS), which has lower binding energy than the cocrystalized ligand pyridoxal 5 phosphate (PLP), using a computer-aided drug design approach including pharmacophore modeling, virtual screening, and in silico ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) evaluation. The screening and molecular docking of 4254 compounds obtained from the PubChem database were carried out using AutoDock vina, while a post-screening analysis was carried out using Discovery Studio. The best three hits were compounds with the PubChem IDs 118614633, 135715279, and 155773276, possessing binding affinities of -9.1, -8.9, and -8.8 kcal/mol, respectively. The in silico ADMET prediction showed that the pharmacokinetic properties of the best hits were relatively good. The optimization of the best three hits via scaffold hopping gave rise to 187 compounds, and they were docked against StOASS; this revealed that lead compound 1 had the lowest binding energy (-9.3 kcal/mol) and performed better than its parent compound 155773276. Lead compound 1, with the best binding affinity, has a hydroxyl group in its structure and a change in the core heterocycle of its parent compound to benzimidazole, and pyrimidine introduces a synergistic effect and consequently increases the binding energy. The stability of the best hit and optimized compound at the StOASS active site was determined using RMSD, RMSF, radius of gyration, and SASA plots generated from a molecular dynamics simulation. The MD simulation results were also used to monitor how the introduction of new functional groups of optimized compounds contributes to the stability of ligands at the target active site. The improved binding affinity of these compounds compared to PLP and their toxicity profile, which is predicted to be mild, highlights them as good inhibitors of StOASS, and hence, possible antimicrobial adjuvants.

Nigella sativa as an antibiotic alternative to promote growth and enhance health of broilers challenged with Eimeria maxima and Clostridium perfringens

The poultry industry has significant coccidiosis and necrotic enteritis (NE) challenges, leading to high mortality and unacceptable growth without antibiotic treatment. This research explored supplementing Nigella sativa (black cumin) seed oil in poultry feed to mitigate coccidiosis and prevent or lessen NE in broilers. In vivo studies consisted of 384 and 320 Cobb 500 male broiler chicks distributed in a randomized complete block experimental design for trials 1 and 2, respectively. The first trial compared 3 concentrations (1, 2, and 5 mL/kg) of black cumin seed oil (BCSO), and trial 2 compared 2 concentrations (2 and 5 mL/kg) BCSO, with birds challenged with Eimeria maxima and Clostridium perfringens (Cp) strains Cp#6 and Cp#4, respectively. Broiler live performance, NE disease outcomes, and Cp populations were measured for both trials. A commercially available BCSO oil product, determined in a preliminary in vitro study to have the highest anti-Cp activity, was selected for in vivo studies. Gas chromatography-mass spectrometry analysis indicated the major bioactive compounds p-cymene, thymoquinone, carvacrol, and thymol were present in the BCSO. In trial 1 with strain Cp#6, BCSO concentrations of 2 and 5 mL/kg reduced NE lesion score and mortality rate to 1.6% compared with 7.8% for positive control, with no adverse impact on live performance. In trial 2 with strain Cp#4, BCSO reduced NE lesion scores and mortality rate to 35.9% compared with 51.6% for positive control and also improved weight gain when there was a Cp infection in broiler chickens. The current study compared NE in broilers challenged with 2 different Cp strains producing different levels of NE. Following Cp infection, both the population of vegetative cells and spores of Cp in cecal contents decreased for all treatments in trial 2. In conclusion, BCSO at concentrations of 2 and 5 mL/kg enhanced broiler live performance and alleviated NE and has potential as a natural, non-medication antimicrobial nutritional supplement for use as a feed additive in chickens.

The niche of a stress-tolerant specialist, Dinophysis acuminata, in a coastal upwelling system

Dinophysis acuminata, the main cause of shellfish harvesting bans in Europe, blooms in the Galician Rías (NW Spain) throughout the upwelling season (ca. March to September). Here we illustrate rapid changes in vertical and across ría-shelf distributions of diatoms and dinoflagellates (including D. acuminata vegetative and small cells) in Ría de Pontevedra (RP) and Ría de Vigo (RV) during transitions from spin-down to spin-up phases of upwelling cycles. A subniche approach based on a Within Outlying Mean Index (WitOMI) showed that under the transient environmental conditions met during the cruise, both vegetative and small cells of D. acuminata colonized the Ria and Mid-shelf subniches, exhibiting good tolerance and extremely high marginality, in particular the small cells. Bottom-up (abiotic) control overwhelmed biological constraints, and shelf waters became a more favourable environment than the Rías. Contrasting higher biotic constraints inside the Rías were found for the small cells, with a subniche possibly controlled by unsuitable physiological status (notwithstanding the higher density) of the vegetative cell population. Results here on behaviour (vertical positioning) and physiological traits (high tolerance but very specialized niche) of D. acuminata give new insights into the ability of this species to remain in the upwelling circulation system. Higher shelf-ría exchanges in the Ría (RP) with more dense and persistent D. acuminata blooms reveal the relevance of transient event-scales and species- and site-specific characteristics to the fate of these blooms. Earlier statements about simple linear relationships between average upwelling intensities and the recurrence of Harmful algae bloom (HAB) events in the Galician Rías Baixas are questioned.

A method for quantifying sporulation efficiency and isolating meiotic progeny in non-GMO strains of Saccharomyces cerevisiae.

Meiotic mapping, a linkage-based method for analyzing the recombinant progeny of a cross, has long been a cornerstone of genetic research. The yeast Saccharomyces cerevisiae is a powerful system because it is possible to isolate and cultivate the four products (spores) of a single meiotic event. However, the throughput of this process has historically been limited by the process of identifying tetrads in a heterogeneous population of vegetative cells, tetrads, and dyads followed by manual separation (dissection) of the spores contained in a tetrad. To date, methods that facilitate high throughput characterization and isolation of meiotic progeny have relied on genetic engineering. Here, we characterize the ability of the fluorescent dye DiBAC4 (5) to stain yeast tetrads and dyads as well as to adhere to spores following bulk tetrad disruption. Applications include quantitative assays of sporulation rates and efficiency by flow cytometry as well as enrichment of intact tetrads, dyads, or disrupted spores by fluorescence-activated cell sorting in strains that have not been genetically modified.

A preliminary study on the effect of storage temperatures on the population of Bacillus cereus in dry ginger powder

The formation of spores and increase in population of vegetative cells of Bacillus cereus associated with foodborne diseases is dependent on favourable temperature. In this study, B. cereus in a slant obtained from Microbiology Laboratory, University of Port Harcourt was confirmed based on morphological and biochemical tests and inoculated into dry ginger powder using a sterile pipette. The samples were stored at ambient temperature (25°C), refrigeration temperature (4°C) and freezer temperature (-18°C) for 21 days and the microbial counts of B. cereus was monitored at 7 days interval using Bacillus cereus agar base and standard microbiological methods. The result obtained showed that B. cereus steadily increased in population under the storage conditions. The highest microbial count recorded for B. cereus in dry ginger powder stored at 25°C, 4°C and -18°C was 7.15×101 ±0.036, 1.07×102 ± 0.061 and 2.91×102 ± 0.070 CFU/g, respectively. Although the values did not exceed 105 cells/g required to manifest foodborne illness in humans, it remains a risk to public health due to increasing population of B. cereus in dry ginger powder under the storage conditions.

P.765 The role of N-acetyl-D-glucosamine kinase in protecting proteinopathies

This study evaluates the potential of continuous wave Ultraviolet C light (UV-C) and broad-spectrum intense pulsed light (in this study referred to as High Intensity Light Pulses, HILP) for the inactivation of pathogens of public concern in powdered infant formula (PIF) producers. To achieve this goal a sequential set of experiments were performed, firstly in clear liquid media, secondly on the surface of spherical beads under agitation and, finally in PIF. L. innocua was the most sensitive microorganism to both technologies under all conditions studied with reductions exceeding 4 log10 cycles in PIF. In the clear liquid medium, the maximum tolerance to light was observed for C. sakazakii against UV-C light and for B. subtilis spores against HILP, with a fluence of approximately 17 mJ/cm2 required for a 1 log10 cycle inactivation (D value) of each species. In PIF it was possible to inactivate >99% of the vegetative cell populations by HILP with a fluence of 199 mJ/cm2 and of B. subtilis spores by doubling the fluence. By contrast, for UV-C treatments a fluence of 2853 mJ/cm2 was needed for 99.9% reduction of C. sakazakii, which was the most light-resistant microorganism to UV-C. Results here obtained clearly show the potential for light-based interventions to improve PIF microbiological safety.

Tracking Alexandrium catenella from seed-bed to bloom on the southern coast of Korea

Alexandrium catenella was tracked from seed-bed to bloom at a hot spot of cyst deposition on the southern coast of Korea from June 2016 to Feb. 2020. Changes in cyst abundance and germinability from sediment, as well as the vegetative cell abundance and encystment in the water column were intensively monitored. Cyst germination of ca. 73% occurred synchronously in November of 2016 to 2019, when bottom water temperature was around 15 °C. After mass germination, vegetative cells formed a seed populations at low density (<10 cells L−1) during winter. Overwintering populations initiated growth in March and then proliferated into high density (ca. 4 × 104 cells L−1) spring blooms in mid-April 2017 when moderate temperature (15 °C) was recorded. There was no bloom in spring of 2018 and 2019, but small vegetative populations developed. Decline of the spring bloom was followed by massive encystment and an increase in Noctiluca abundance. An average spring encystment ratio of 0.002 was estimated for the study years. Newly formed cysts lay dormant during the warm season lasting about six months and then seeded the next population of vegetative cells. An average contribution ratio of cells recruited from the sediment was ca. 0.09 for seeding winter populations. The range in shift ratios for spring production of a daughter cyst population to prior cyst abundance of the mother population in fall was 0.1 to 0.6 for consecutive years, depending on annual variation of local environments. Tracking mass transformation of A. catenella cysts will contribute to more effective science based management of paralytic shellfish poisoning on the southern Korean coast.

Impact of temperature and oxygen on the fate of Bacillus weihenstephanensis in a food-based medium

The capacity of the Bacillus weihenstephanensis KBAB4 strain, a psychrotolerant species of the B. cereus sensu lato group, to multiply in carrot broth at 8 °C and 30 °C, in presence or absence of oxygen was determined. In aerobic carrot broth tyndallized in presence of oxygen, at both temperatures, the population of vegetative cells of B. weihenstephanensis inoculated at a level of 103 or 106 CFU/ml dropped immediately. After 16 h at 30 °C, B. weihenstephanensis reached around 103 CFU/ml, indicating that some vegetative cells had survived and multiplied, with lipid inclusions accumulated in cells, indicating possible stressing conditions. At 8 °C, no multiplication of B. weihenstephanensis was observed during 3 days to at least 12 days, depending of carrot broth batches. In anaerobic carrot broth tyndallized without oxygen, the vegetative cells of B. weihenstephanensis were not killed upon inoculation and multiplied in the broth at both 30 °C and 8 °C. Comparison with results from previous studies shows that B. weihenstephanensis behaves differently in carrot broth and in laboratory media at 8 °C with regards to presence or absence of oxygen.

Effects of diluents, temperature and pH on the enumeration and growth kinetics of Alicyclobacillus acidoterrestris in standard growth media

This study reports the effects of dilutions in distilled water, 0.85% saline, 0.10% peptone water and phosphate-buffered saline on the viability of Alicyclobacillus acidoterrestris. Only peptone water caused a significant underestimation of viable populations of vegetative cells. Effects of temperature and pH on the growth kinetics of A. acidoterrestris in yeast starch glucose (YSG) media were characterized using a two-factored Central Composite Design (CCD). Response Surface Methodology was applied to quantify their influences on lag time, growth rate, and population change. Rates ranged from −0.37 (inactivating) to 1.07 (growth), while population change varied from −3.11 to 2.89 log. Values significantly fitted into a linear model for the growth rate response and a quadratic model for the population change response. pH was observed to be the significant factor affecting the response variables, having significant quadratic effects. Model validation with temperature and pH combinations unique from the CCD showed that predictions were within acceptable error margins for the population change model, while the growth rate model exhibited limited success rate. The results obtained in this study provide information on growth behaviors of A. acidoterrestris in standard media and can be further used in researches dealing with its maintenance and propagation.

Light based technologies for microbial inactivation of liquids, bead surfaces and powdered infant formula

This study evaluates the potential of continuous wave Ultraviolet C light (UV-C) and broad-spectrum intense pulsed light (in this study referred to as High Intensity Light Pulses, HILP) for the inactivation of pathogens of public concern in powdered infant formula (PIF) producers. To achieve this goal a sequential set of experiments were performed, firstly in clear liquid media, secondly on the surface of spherical beads under agitation and, finally in PIF. L. innocua was the most sensitive microorganism to both technologies under all conditions studied with reductions exceeding 4 log10 cycles in PIF. In the clear liquid medium, the maximum tolerance to light was observed for C. sakazakii against UV-C light and for B. subtilis spores against HILP, with a fluence of approximately 17 mJ/cm2 required for a 1 log10 cycle inactivation (D value) of each species. In PIF it was possible to inactivate >99% of the vegetative cell populations by HILP with a fluence of 199 mJ/cm2 and of B. subtilis spores by doubling the fluence. By contrast, for UV-C treatments a fluence of 2853 mJ/cm2 was needed for 99.9% reduction of C. sakazakii, which was the most light-resistant microorganism to UV-C. Results here obtained clearly show the potential for light-based interventions to improve PIF microbiological safety.

Potential of lactoferrin to prevent antibiotic-induced Clostridium difficile infection.

ObjectivesClostridium difficile infection (CDI) is a global healthcare problem. Recent evidence suggests that the availability of iron may be important for C. difficile growth. This study evaluated the comparative effects of iron-depleted (1% Fe3+ saturated) bovine apo-lactoferrin (apo-bLf) and iron-saturated (85% Fe3+ saturated) bovine holo-lactoferrin (holo-bLf) in a human in vitro gut model that simulates CDI.MethodsTwo parallel triple-stage chemostat gut models were inoculated with pooled human faeces and spiked with C. difficile spores (strain 027 210, PCR ribotype 027). Holo- or apo-bLf was instilled (5 mg/mL, once daily) for 35 days. After 7 days, clindamycin was instilled (33.9 mg/L, four times daily) to induce simulated CDI. Indigenous microflora populations, C. difficile total counts and spores, cytotoxin titres, short chain fatty acid concentrations, biometal concentrations, lactoferrin concentration and iron content of lactoferrin were monitored daily.ResultsIn the apo-bLf model, germination of C. difficile spores occurred 6 days post instillation of clindamycin, followed by rapid vegetative cell proliferation and detectable toxin production. By contrast, in the holo-bLf model, only a modest vegetative cell population was observed until 16 days post antibiotic administration. Notably, no toxin was detected in this model. In separate batch culture experiments, holo-bLf prevented C. difficile vegetative cell growth and toxin production, whereas apo-bLf and iron alone did not.ConclusionsHolo-bLf, but not apo-bLf, delayed C. difficile growth and prevented toxin production in a human gut model of CDI. This inhibitory effect may be iron independent. These observations suggest that bLf in its iron-saturated state could be used as a novel preventative or treatment strategy for CDI.

Implications of Decreased Nitrite Concentrations on Clostridium perfringens Outgrowth during Cooling of Ready-to-Eat Meats

Increased popularity of natural and organic processed meats can be attributed to the growing consumer demand for preservative-free foods, including processed meats. To meet this consumer demand, meat processors have begun using celery juice concentrate in place of sodium nitrite to create products labeled as no-nitrate or no-nitrite-added meat products while maintaining the characteristics unique to conventionally cured processed meats. Because of flavor limitations, natural cures with celery concentrate typically provide lower ingoing nitrite concentrations for ready-to-eat processed meats than do conventional cures, which could allow for increased growth of pathogens, such as Clostridium perfringens, during cooked product cooling such as that required by the U.S. Department of Agriculture. The objective of this study was to investigate the implications associated with reduced nitrite concentrations for preventing C. perfringens outgrowth during a typical cooling cycle used for cooked products. Nitrite treatments of 0, 50, and 100 ppm were tested in a broth system inoculated with a three-strain C. perfringens cocktail and heated with a simulated product thermal process followed by a typical cooling-stabilization process. The nitrite concentration of 50 ppm was more effective for preventing C. perfringens outgrowth than was 0 ppm but was not as effective as 100 ppm. The interaction between nitrite and temperature significantly affected (P < 0.05) C. perfringens outgrowth in both total population and number of vegetative cells. Both temperature and nitrite concentration significantly affected (P < 0.05) C. perfringens spore survival, but the interaction between nitrite and temperature did not have a significant effect (P > 0.05) on spore outgrowth. Results indicate that decreased nitrite concentrations (50 ppm) have increased potential for total C. perfringens population outgrowth during cooling and may require additional protective measures, such as faster chilling rates.

Synergistic efficacy of 405 nm light and chlorinated disinfectants for the enhanced decontamination of Clostridium difficile spores

The ability of Clostridium difficile to form highly resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is being developed for environmental decontamination within hospitals, however further information relating to its sporicidal efficacy is required. This study aims to establish the efficacy of 405 nm light for inactivation of C. difficile vegetative cells and spores, and to establish whether spore susceptibility can be enhanced by the combined use of 405 nm light with low concentration chlorinated disinfectants. Vegetative cells and spore suspensions were exposed to increasing doses of 405 nm light (at 70–225 mW/cm2) to establish sensitivity. A 99.9% reduction in vegetative cell population was demonstrated with a dose of 252 J/cm2, however spores demonstrated higher resilience, with a 10-fold increase in required dose. Exposures were repeated with spores suspended in the hospital disinfectants sodium hypochlorite, Actichlor and Tristel at non-lethal concentrations (0.1%, 0.001% and 0.0001%, respectively). Enhanced sporicidal activity was achieved when spores were exposed to 405 nm light in the presence of the disinfectants, with a 99.9% reduction achieved following exposure to 33% less light dose than required when exposed to 405 nm light alone. In conclusion, C. difficile vegetative cells and spores can be successfully inactivated using 405 nm light, the sporicidal efficacy can be significantly enhanced when exposed in the presence of low concentration chlorinated disinfectants. Further research may lead to the potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures.

Mathematical study of pattern formation accompanied by heterocyst differentiation in multicellular cyanobacterium.

The filamentous cyanobacterium, Anabaena sp. PCC 7120, is one of the simplest models of a multicellular system showing cellular differentiation. In nitrogen-deprived culture, undifferentiated vegetative cells differentiate into heterocysts at ~10-cell intervals along the cellular filament. As undifferentiated cells divide, the number of cells between heterocysts (segment length) increases, and a new heterocyst appears in the intermediate region. To understand how the heterocyst pattern is formed and maintained, we constructed a one-dimensional cellular automaton (CA) model of the heterocyst pattern formation. The dynamics of vegetative cells is modeled by a stochastic transition process including cell division, differentiation and increase of cell age (maturation). Cell division and differentiation depend on the time elapsed after the last cell division, the "cell age". The model dynamics was mathematically analyzed by a two-step Markov approximation. In the first step, we determined steady state of cell age distribution among vegetative cell population. In the second step, we determined steady state distribution of segment length among segment population. The analytical solution was consistent with the results of numerical simulations. We then compared the analytical solution with the experimental data, and quantitatively estimated the immeasurable intercellular kinetics. We found that differentiation is initially independent of cellular maturation, but becomes dependent on maturation as the pattern formation evolves. Our mathematical model and analysis enabled us to quantify the internal cellular dynamics at various stages of the heterocyst pattern formation.

In situ dynamics of cyst and vegetative cell populations of the toxic dinoflagellate Alexandrium catenella in Ago Bay, central Japan.

Temporal changes in the in situ germination flux of cysts and the abundance of vegetative cells of the toxic dinoflagellate Alexandrium catenella were investigated in Ago Bay, central Japan from July 2003 to December 2004. The in situ germination flux (cells m-2 day-1) was measured using 'plankton emergence trap/chambers (PET chambers)'. Germination of the cysts in the sediments occurred continuously during the study, ranging from 52 to 1753 cells m-2 day-1, with no temporal trend. This germination pattern appeared to be promoted by a short mandatory dormancy period for newly formed cysts coupled with a broad temperature window for germination. For the vegetative populations, high abundances (>105 cells m-2) were recorded in the water column from spring to summer and from autumn to early winter. The size of the vegetative populations did not correlate with the cyst germination flux but rather larger vegetative populations were often observed when the water temperature was around 20°C, indicating that bloom development was mainly regulated by the temperature. Nonetheless, the continuous germination pattern of A. catenella is advantageous enabling the germinated cells to immediately exploit favorable bloom conditions.

Inactivation of Alicyclobacillusacidoterrestris Using High Pressure Homogenization and Dimethyl Dicarbonate

Vegetative cells and spores of five strains of Alicyclobacillus acidoterrestris (N-1100, N-1108, N-1096, SAC, and OS-CAJ) were screened for their sensitivity to high pressure homogenization (HPH, 0 to 300 MPa) in Bacillus acidoterrestris thermophilic broth. The most and least resistant strains, SAC and OS-CAJ, respectively, were further tested for their sensitivity to inactivation or growth inhibition by dimethyl dicarbonate (DMDC, 250 ppm). The combined effects of HPH and DMDC were then evaluated against SAC spores over a 24-h period after treatment. HPH alone significantly inactivated (P < 0.05) vegetative cells of all five strains. SAC vegetative cells were least affected by HPH, with only about a 0.5-log reduction after the 300-MPa treatment. Spores were not significantly reduced by HPH for any of the five strains. DMDC reduced the initial vegetative cell population by 2 log CFU/ml and significantly increased the time to reach stationary phase. For spores, a 0.5-log decrease from the initial spore population was achieved and growth was not significantly delayed. No significant difference was found between the two strains. Treatment with DMDC plus HPH slightly enhanced the inactivation effect over a 24-h period compared with treatment with HPH alone, but these differences were statistically inconsistent. Although HPH and DMDC treatments may help control vegetative cells of A. acidoterrestris, these treatments may not provide adequate overall control. Neither treatment, alone or in combination, is very effective against spores.

In situ life-cycle stages of Alexandrium fundyense during bloom development in Northport Harbor (New York, USA)

Knowledge of the specific life-cycle dynamics during harmful algal bloom (HAB) development is essential for understanding and forecasting the onset, evolution and future occurrence of these events. Life-cycle stages of the toxic dinoflagellate Alexandrium fundyense were monitored both in the water column and in the sediments from the onset to the decline of a bloom in Northport Harbor (New York, USA). Moreover, excystment and encystment were investigated in situ through the deployment of emergence and sediment traps, respectively. The bloom, the largest ever recorded on the east coast of the US south of Massachusetts, persisted for 6 weeks between April and June 2008, and reached maximum vegetative cell abundances of 1.3×106cellsl−1. Resting cysts in the surface sediments were quantified at the onset of the bloom, all of which germinated during the development of the bloom. Excystment of these resting cysts provided inoculum of vegetative cells for bloom development. In the water column, first detection of planozygotes occurred during the exponential phase of the bloom at vegetative cell abundances of ∼104cellsl−1. Nonmotile planozygotes and resting cysts were observed in the sediment traps before the first peak of vegetative cells, coinciding with the detection of planktonic planozygotes. The estimated encystment and planozygote percentages were relatively low, indicating that a small proportion of the vegetative cell population was involved in sexual reproduction. However, encystment was a crucial process for replenishing the cyst stock of the A. fundyense population in the sediments as cyst densities were low before the bloom but high after it. For the first time, formation of pellicle cysts in the field by A. fundyense was observed, which coincided with high vegetative cell abundances in the water column during the bloom.

Cysteine biosynthesis, oxidative stress and antibiotic resistance in Salmonella typhimurium

The efficacy of antibiotics varies under different growth conditions due to the induction of specific or more general defense pathways, but the mechanisms are not completely understood. Actively swarming Salmonella show elevated resistance to many types of antibiotics. Previously, we had shown that cysteine biosynthesis was important for the induced antibiotic resistance phenotype of swarm cells. Here we examine the connection of cysteine to oxidative stress and demonstrate that the antioxidant properties of cysteine or cysteine-derived metabolites contribute to the antibiotic resistance in both vegetative and swarm cell populations. We observed that cys auxotrophs were oxidatively stressed, and in wild-type cells expression of the cys regulon was induced during periods of oxidative stress. In swarm cells, we found a 6-fold increase in reduced glutathione compared to swim cells and a corresponding increased resistance to oxidants. Wild-type and cys auxotrophs exhibited the same sensitivities to gentamicin, polymyxin and ciprofloxacin when grown anaerobically, suggesting that induced oxidative stress defense was contributing to elevated antibiotic resistance in swarm cells aerobically. Induction of the CysB regulon by addition of exogenous inducer resulted in elevated antibiotic resistance independently of swarming.

Inactivation of Clostridium perfringens spores and vegetative cells by photolysis and TiO 2 photocatalysis with H 2O 2

Due to public health concerns related to the generation of dangerous by-products from conventional systems of water disinfection, innovative technologies based on the generation of oxidant radicals are being developed. The aim of this work is to evaluate the bactericidal activity of different treatments with light ( λ: 320–800 nm), TiO 2 (1 g L −1) and H 2O 2 (0.04 mM) on the viability of vegetative cells and spores of Clostridium perfringens. After spiking a natural water sample (from the Ebro River, Zaragoza (Spain)), the population of vegetative cells was of 10 8 CFU·100 mL −1 and of spores about 10 3 CFU·100 mL −1. Treatments without radiation source (TiO 2, H 2O 2, TiO 2/H 2O 2) show a poor level of inactivation (<0.5 log) on both bacterial forms. The light treatment achieves a vegetative cell inactivation of 1.2 log after 5 min of treatment and <0.5 log on spores after 30 min. The combined light/TiO 2 system increases the level of disinfection with a vegetative cell removal in the order of 6 log after 5 min and 0.6 log of spores after 5 min. Light/H 2O 2 and light/TiO 2/H 2O 2 treatments also significantly increase the disinfection of vegetative cells of C. perfringens (>6 log). Regarding spores, light/H 2O 2 and light/TiO 2/H 2O 2 treatments achieve constant inactivation of 1 log after 5 min of treatment. The application of a light/TiO 2/H 2O 2 treatment does not increase the level of inactivation with regard to the level reached by the light/TiO 2 and light/H 2O 2 systems. This fact shows there is no a significant interaction between TiO 2 and H 2O 2 under the conditions studied.

The role of resting cysts in Alexandrium minutum population dynamics

Abstract The role of resting cysts on the development of Alexandrium minutum blooms in a typical Mediterranean semi-enclosed water body (Arenys de Mar Harbor, NW Mediterranean) was studied by means of matrix and dynamic population models. We used a series of scenarios, constrained when possible by experimentally measured parameters to test whether excystment and encystment fluxes and changes in the dormancy period had a major effect on bloom intensity and duration. The results of the simulations highlighted the importance of knowing not only the magnitude and variability of growth and life-cycle transition rates, but also those of loss rates (both in the water column and in the sediment) due to physical or biological factors. Given the maximum encystment rates determined for A. minutum in the study area (0.01 d −1 ), this process contributed to reduce the peak concentrations of vegetative cells but did not have a dominant effect on bloom termination. Excystment fluxes could contribute to enhance population densities of vegetative cells during times or low or negative net growth rate and during the initial phases of a bloom, but once exponential growth had started, additional excystment had negligible effect on bloom magnitude. However, even if cysts did not contribute to larger blooms, they could represent a safety mechanism for reintroduction of the species when the vegetative cell population went extinct due to unfavorable environmental conditions. Increasing the dormancy time exposed newly formed cysts to a longer period of losses in the sediment that reduced the concentration of excystment-ready sediment cysts and decreased excystment fluxes. More complex models will be needed to explore the implications of different life-cycle strategies in a wider natural ecological context.