Effects of three heavy metals on the bacteria growth kinetics: a bivariate model for toxicological assessment

Mechanism of the antimicrobial activity induced by phosphatase inhibitor sodium ortho-vanadate

The present study describes a novel antimicrobial mechanism based on Sodium Orthovanadate (SOV), an alkaline phosphatase inhibitor. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed to examine the surface morphologies of the test organism, Escherichia coli (E. coli), during various antibacterial phases. Our results indicated that SOV kills bacteria by attacking cell wall growth and development, leaving E. coli's outer membrane intact. Our antimicrobial test indicated that the MIC of SOV for both E. coli and Lactococcus lactis (L. lactis) is 40 μM. A combination of quantum mechanical calculations and vibrational spectroscopy revealed that divanadate from SOV strongly coordinates with Ca2+ and Mg2+, which are the activity centers for the phosphatase that regulates bacterial cell wall synthesis. The current study is the first to propose the antibacterial mechanism caused by SOV attacking cell wall.

Simultant: simultaneous curve fitting of functions and differential equations using analytical gradient calculations

BACKGROUND

The initial step in comparing mathematical models to experimental data is to do a fit. This process can be complicated when either the mathematical models are not analytically solvable (e.g. because of nonlinear differential equations) or when the relation between data and models is complex (e.g. when some fitting parameters must be shared between many data sets).

RESULTS

We introduce Simultant, a software package that allows complex fitting setups to be easily defined using a simple graphical user interface. Fitting functions can be defined directly as mathematical expressions or indirectly as the solution to specified ordinary differential equations. Analytical gradients of these functions, including the solution of differential equations, are automatically calculated to provide fast fitting even for functions with many parameters. The software enables easy definition of complex fitting setups in which parameters can be shared across both data sets and models to allow simultaneous fits to be performed.

CONCLUSIONS

Simultant exploits differentiable programming and simplifies modern fitting approaches in a unified graphical interface.

Kinetics of Bacterial Adaptation, Growth, and Death at Didecyldimethylammonium Chloride sub-MIC Concentrations

Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) are standard indexes for determining disinfection effectiveness. Nevertheless, they are static values disregarding the kinetics at sub-MIC concentrations where adaptation, growth, stationary, and death phases can be observed. The understanding of these dynamic mechanisms is crucial to designing effective disinfection strategies. In this study, we studied the 48 h kinetics of Bacillus cereus and Escherichia coli cells exposed to sub-MIC concentrations of didecyldimethylammonium chloride (DDAC). Two mathematical models were employed to reproduce the experiments: the only-growth classical logistic model and a mechanistic model including growth and death dynamics. Although both models reproduce the lag, exponential and stationary phases, only the mechanistic model is able to reproduce the death phase and reveals the concentration dependence of the bactericidal/bacteriostatic activity of DDAC. This model could potentially be extended to study other antimicrobials and reproduce changes in optical density (OD) and colony-forming units (CFUs) with the same parameters and mechanisms of action.

Modeling the Inhibition Kinetics of Curcumin, Orange G, and Resveratrol with Amyloid-β Peptide

The β-amyloid (Aβ) protein aggregation into toxic forms is one of the major factors in the Alzheimer's disease (AD) pathology. Screening compound libraries as inhibitors of Aβ-aggregation is a common strategy to discover novel molecules as potential therapeutics in AD. In this regard, thioflavin T (ThT)-based fluorescence spectroscopy is a widely used in vitro method to identify inhibitors of Aβ aggregation. However, conventional data processing of the ThT assay experimental results generally provides only qualitative output and lacks inhibitor-specific quantitative data, which can offer a number of advantages such as identification of critical inhibitor-specific parameters required to design superior inhibitors and reduce the need to conduct extensive in vitro kinetic studies. Therefore, we carried out mathematical modeling based on logistic equation and power law (PL) model to correlate the experimental results obtained from the ThT-based Aβ40 aggregation kinetics for small-molecule inhibitors curcumin, orange G, and resveratrol and quantitatively fit the data in a logistic equation. This approach provides important inhibitor-specific parameters such as lag time λ, inflection point τ, maximum slope v _m, and apparent rate constant k _app, which are particularly useful in comparing the effectiveness of potential Aβ40 aggregation inhibitors and can be applied in drug discovery campaigns to compare and contrast Aβ40 inhibition data for large compound libraries.

Bio-removal of Pb, Cu, and Ni from solutions as nano-carbonates using a plant-derived urease enzyme-urea mixture

This study focuses on utilizing a plant-derived urease enzyme (PDUE)-urea mixture to remove heavy metals from water as constituents of nano-carbonate minerals. The bio-removal process was conducted by individually mixing PbCl₂, CuCl₂, and NiCl₂ solutions with a PDUE-urea mixture, followed by incubation for 24 h at 23 ± 2 °C. The preliminary results revealed that the proposed method exhibited high Pb removal efficiency (˃ 99%) in a short time (8 h); meanwhile, moderate Cu and Ni removal efficiencies (67.91% and 58.49%, respectively) were obtained at the same incubation time. The concentration of heavy metals (50-200 mM) had an insignificant effect on the bio-removal rate, indicating that the PDUE-urea mixture is highly effective for the removal of heavy metals at different concentrations. The bio-removal process involved the transformation of soluble heavy metals into insoluble carbonate materials. A spherically shaped nano-cerussite (4-15 nm), a malachite hexahydrate nanosheet (thickness 8 nm), and an ultrafine micro-hellyerite (thickness 0.3 μm) were the main minerals produced by the Pb, Cu, and Ni bio-removal processes, respectively. As a beneficial application, nano-cerussite was used as an additive in an alkali-activated slag/ceramic waste-based geopolymeric coating. A preliminary study proved that increasing the nano-cerussite content enhanced the resistance of the geopolymeric coating to sulfur-oxidizing bacteria, which is detrimental to normal concrete, particularly in sewer systems.

Microbial community successional patterns in offshore sediments impacted by chemical pollution from Taizhou and Xiamen Cities in China

An Illumina-based next-generation sequencing was employed to characterise the sediment microbiome adjacent to coastal industrial and tourist cities, Taizhou and Xiamen, in China, and their associations with chemical pollution were explored. The results indicated that chemical pollution of sediments from Taizhou was higher than that from Xiamen. The number of sediment bacterial genera was negatively (Taizhou) or positively (Xiamen) correlated with offshore distance, owing to shifts in the primary and secondary status of organic matter and chemical pollutants for the promotion or inhibition of the sediment microbiome. The total number of the operational taxonomic units (OTUs) in sediments from Taizhou was larger than from Xiamen, while the number of core OTUs was smaller indicating that Taizhou had more impact on core microbes in sediments than Xiamen. This study suggests that chemical pollutants and organic matter result in different co-regulation of the off-shore sediment microbiome of coastal industrial and tourist cities.

A prophylactic multi-strain probiotic treatment to reduce the absorption of toxic elements: In-vitro study and biomonitoring of breast milk and infant stools

Potential exposure to toxic elements initially occurs during gestation and after birth via breast milk, which is the principal source of nutrients for infants during the first months of life. In this study, we evaluated whether maternal oral supplementation with a multi-strain probiotic product can protect infants from exposure to arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) via breast milk. In-vitro studies of the bacterial strains present in this probiotic product showed a high bacterial tolerance for As, Cd, Hg, and Pb, and good binding capacity for Cd, Hg, and Pb (72%, 81%, and 64%, respectively) within 1 h of contact. We evaluated concentrations (5 mg L^-1 for Cd and Pb, and 2 mg L^-1 for Hg) that largely exceeded the provisional tolerable weekly intake of these toxic elements via food or water applicable for human consumption. Changes in the levels of these elements in breast milk and newborn stools were evaluated in the control (orally supplemented with placebo) and experimental (orally supplemented with probiotic) groups at birth (t0), 15 days (t15), and 30 days (t30) after delivery. Elemental analysis of breast milk did not show significant differences between the control and experimental groups at different stages of lactation; however, stool samples obtained from newborns of mothers supplemented with the probiotic product showed that Cd levels were significantly reduced (by 26%) at t15 compared with the levels of the controls. Our data did not show an association between concentration of toxic elements in breast milk and that in newborn stools. Indeed, the concentration of Cd, Hg, and Pb in breast milk decreased during the lactation period, whereas the levels of these elements in newborn stools were stable over time. Although our in-vitro data indicate that the consortium of these probiotic strains can absorb toxic compounds, this study was limited by its small sample size and potential uncontrolled confounding effects, such as maternal diet and lifestyle. Therefore, we could not confirm whether prophylactic use of this probiotic product can reduce the absorption of toxic elements. The risk assessment in the studied population evidenced a margin of exposure (MOE) of 1, or between 1 and 10 for Pb, and lower than 50 for As. This poses a potential risk for breastfed infants, indicating that interventions aimed to avoid breastfeeding-related health risks remain a major challenge in public health.

Microbial activity and biodiversity responding to contamination of metal(loid) in heterogeneous nonferrous mining and smelting areas

The combined contamination of nonferrous metal(loid) mining and smelting areas is a global issue, in need of urgent management. To our knowledge, this is the first report of microbial activities by microcalorimetry in specific nonferrous metal(loid) tailings with oligonutrition and high contents of toxic metal(loid)s. Dynamics of bacterial diversity were also characterized. Here we show that tailings had low microbial activities (P_max = 64.1-331 μW g^-1), which were accelerated by the presence of dipotassium phosphate (P_max = 346-856 μW g^-1), as measured by microcalorimetry. Frequent detection of S- and metal-resistant related genera and differences of Thiobacillus and Acidithiobacillus abundances indicated that the tailings were in an early stage of acidification. It has been further confirmed by the presence of a weak acid environment and secondary sulfur associated minerals, such as Sb₂S₃, FeAsS, FeS₂, and CuFeS₂. During the acidification process, phosphate, metal(loid)s, and microbial activity were correlated to the bacterial communities. It is suggested that the bacterial communities have metabolic capacities with a high potential for the use in management processes of multi-contaminated nonferrous metalliferous tailings.

Exploring the survival tactics and plant growth promising traits of root-associated bacterial strains under Cd and Pb stress: A modelling based approach

The study represents a microbial method for reducing heavy metal stress in terrestrial environment. Two rhizobacterial strains Pantoea agglomerance (PC1) and Pseudomonas aeruginosa (SA) having the ability to tolerate Cd²⁺ and Pb²⁺ ions stress, were employed in this study. The growth promotion and survival tactics of the strains under metal stress were explored through kinetic growth model using logistic equation, Luedeking-Piret model and Box Behnken design. Study also involves the interaction of strains with Zea mays L. under Cd²⁺ and Pb²⁺ ions stress. Results revealed that both strains have the potential to tolerate 500 mg L^-1 of Cd²⁺ and Pb²⁺, ions and maintained the plant growth promoting traits. The Luedeking-Piret model estimated the maximum value of IAA on biomass growth (Y_P/X) 5.377 μg g^-1 and 10.3 μg g^-1 under Cd²⁺ ions, while 7.742 μg g^-1 and 18.071 μg g^-1 under Pb²⁺ ions stress for strains SA and PC1, respectively. Further, phosphate solubilization activity was optimized with the help of response surface methodology using Box Behnken Design. The optimum solubilization by strain PC1 and SA was achieved at 100 and 150 mg L^-1 of Cd²⁺, and 150 and 200 mg L^-1 of Pb²⁺ ion concentration at the pH range 6.75 and 7.5 respectively. The interactive study with Zea mays L. showed significant increase in seed germination in the presence of Cd²⁺ and Pb²⁺ ions thereby proving them as potent plant growth promoters and metal stress reducing biological agents. Hence, the findings of the study suggest that rhizobacterial strains could be a sustainable tool for restoration of metal contaminated sites.

Implications in studies of environmental risk assessments: Does culture medium influence the results of toxicity tests of marine bacteria?

Two marine bacterial populations (Roseobacter sp. and Pseudomonas litoralis) were exposed to different concentrations of zinc (300, 625, 1250, 2000, 2500 and 5000 mg L^-1) and cadmium (75, 250, 340, 500 and 1000 mg L^-1) using two culture media (full nutrient Marine Broth 2216 "MB" and 1:10 (vol/vol) dilution with seawater of Marine Broth 2216 "MB_SW"), in order to assess population responses depending on the culture medium and also potential adverse effects associated with these two metals. Different responses were found depending on the culture medium (Bacterial abundance (cells·mL^-1), growth rates (μ, hours^-1), and production of Extracellular Polysaccharides Substances (EPS) (μg glucose·cells^-1). Results showed negative effects in both strains after the exposure to Zn treatments. Both strains showed highest metal sensitivity at low concentrations using both culture media. However, different results were found when exposing the bacterial populations to Cd treatments depending on the culture medium. Highest toxicity was observed using MB at low levels of Cd concentrations, whereas MB_SW showed toxicity to bacteria at higher concentrations of Cd. Results not only showed adverse effects on Roseobacter sp. and Pseudomonas litoralis associated with the concentration of Zn and Cd, but also confirm that depending on the culture medium results can differ. This work suggests MB_SW as an adequate culture medium to study metal toxicity bioassays in order to predict realistic effects on marine bacterial populations.

Simulating CO2 leakage from sub-seabed storage to determine metal toxicity on marine bacteria

CO₂ storage in sub-seabed marine geological formations has been proposed as an adequate strategy to mitigate high CO₂ concentration from the atmosphere. The lack of knowledge about the potential risks of this technology on marine bacteria population in presence of metals has lead us to perform laboratory-scale experiments in order to evaluate its consequences. Thus, the effects of Zn and Cd were studied under acid conditions on Roseobacter sp. and Pseudomonas litoralis. Bacterial abundance (cellsmL^-1), growth rates (μ, h^-1), relative inhibitory effects of CO₂ (RI_CO2), and production of Extracellular Polysaccharides Substances (EPS) (μgGlucosecells^-1) were evaluated. A decreasing exopolysaccharides (EPS) production was found under low pH. Bacterial abundance as well as growth rates showed negative effects. Data obtained in this work are useful to determine the potential effects associated with enrichment of CO₂ and metals on the marine ecosystem.

Effect of organic carbon and metal accumulation on the bacterial communities in sulphidogenic sediments

A unique geochemical setting in Lake Cadagno, Switzerland, has led to the accumulation of insoluble metal sulphides in the sedimentary record as the result of past airborne pollution. This offers an exceptional opportunity to study the effect of these metals on the bacterial communities in sediments, and in particular to investigate further the link between metal contamination and an increase in the populations of endospore-forming bacteria observed previously in other metal-contaminated sediments. A decrease in organic carbon and total bacterial counts was correlated with an increase in the numbers of endospores in the oldest sediment samples, showing the first environmental evidence of a decrease in nutrient availability as a trigger of sporulation. Proteobacteria and Firmicutes were the two dominant bacterial phyla throughout the sediment, the former in an area with high sulphidogenic activity, and the latter in the oldest samples. Even though the dominant Firmicutes taxa were stable along the sediment core and did not vary with changes in metal contamination, the prevalence of some molecular species like Clostridium sp. was positively correlated with metal sulphide concentration. However, this cannot be generalized to all endospore-forming species. Overall, the community composition supports the hypothesis of sporulation as the main mechanism explaining the dominance of endospore formers in the deepest part of the sediment core, while metal contamination in the form of insoluble metal sulphide deposits appears not to be linked with sporulation as a mechanism of metal tolerance in this sulphidogenic ecosystem.

Inhibition of selected bacterial growth by three hydrocarbons: mathematical evaluation of toxicity using a toxicodynamic equation

The individual toxicity of different hydrocarbons (naphthalene, cyclododecane and aniline) on the growth of selected bacteria (Pseudomonas sp., Phaeobacter sp. and Leuconostoc mesenteroides) was studied by means of a toxicodynamic model combination of two sigmoid equations (logistic and Weibull). All the toxicological effects on growth parameters and kinetic properties were characterized and the global toxicity of such chemicals was evaluated. It was observed that two kinetic parameters (maximum growth and maximum growth rate) were in almost all cases influenced by the hydrocarbons studied. Aniline was less toxic than cyclododecane and naphthalene. The presented approach is a reasonable starting point for understanding and modeling complete and real assessment of chemical toxic effects on bacterial growths. The values of EC50,τ could be used for a most efficient comparison of the individual toxicity of chemicals.

Removal of cadmium by Lactobacillus kefir as a protective tool against toxicity

The aim of this work was to evaluate the capacity of Lactobacillus kefir strains to remove cadmium cations and protect eukaryotic cells from cadmium toxicity. Lb. kefir CIDCA 8348 and JCM 5818 were grown in a 1/2 dilution of MRS broth supplemented with Cd(NO3)2 ranging 0 to 1 mM. Growth kinetics were followed during 76 h at 30 °C by registering optical density at 600 nm every 4-10 h. The accumulated concentration of cadmium was determined on cultures in the stationary phase by atomic absorption. The viability of a human hepatoma cell line (HepG2) upon exposure to (a) free cadmium and (b) cadmium previously incubated with Lb. kefir strains was evaluated by determining the mitochondrial dehydrogenase activity. Lb. kefir strains were able to grow and tolerate concentrations of cadmium cations up to 1 mM. The addition of cadmium to the culture medium increased the lag time in all the concentrations used. However, a decrease of the total biomass (maximum Absorbance) was observed only at concentrations above 0.0012 and 0.0011 mM for strains CIDCA 8348 and JCM 5818, respectively. Shorter and rounder lactobacilli were observed in both strains upon microscopic observations. Moreover, dark precipitates compatible with intracellular precipitation of cadmium were observed in the cytoplasm of both strains. The ability of Lb. kefir to protect eukaryotic cells cultures from cadmium toxicity was analysed using HepG2 cells lines. Concentrations of cadmium greater than 3×10(-3) mM strongly decreased the viability of HepG2 cells. However, when the eukaryotic cells were exposed to cadmium pre-incubated 1 h with Lb. kefir the toxicity of cadmium was considerably lower, Lb. kefir JCM 5818 being more efficient. The high tolerance and binding capacity of Lb. kefir strains to cadmium concentrations largely exceeding the tolerated weekly intake (TWI) of cadmium for food (2.5 μg per kg of body weight) and water (3 μg/l) addressed to human consumption, is an important added value when thinking in health-related applications.

Toxicity of four spill-treating agents on bacterial growth and sea urchin embryogenesis

The toxicity of spill-treating agents (STAs) is a topic that needs to be assessed prior to their potential application in environmental disasters. The aim of the present work was to study the effects of four commercial STAs (CytoSol, Finasol OSR 51, Agma OSD 569 and OD4000) on the growth of marine (Phaeobacter sp., Pseudomonas sp.) and terrestrial (Leuconostoc mesenteroides) bacteria, and sea urchin (Paracentrotus lividus) embryolarval development. In general, STA did not inhibit significantly the biomass production of the tested marine bacteria. Finasol OSR 51 and OD4000 clearly inhibited the growth of L. mesenteroides and an accurate description of the kinetics was provided by a proposed bivariate equation. For this species, a global parameter (EC50,τ) was defined to summarize the set of growth kinetics. Using this parameter Finasol OSR 51 was found to be less toxic (754μL L(-1)) than OD4000 (129μL L(-1)). For the sea urchin embryo assay, the ranking of toxicity as EC50 (μL L(-1)) was Agma OSD 569 (34.0)<CytoSol (26.3)<OD4000 (2.2)<Finasol OSR 51 (1.2).

Modeling of chemical inhibition from amyloid protein aggregation kinetics

Backgrounds

The process of amyloid proteins aggregation causes several human neuropathologies. In some cases, e.g. fibrillar deposits of insulin, the problems are generated in the processes of production and purification of protein and in the pump devices or injectable preparations for diabetics. Experimental kinetics and adequate modelling of chemical inhibition from amyloid aggregation are of practical importance in order to study the viable processing, formulation and storage as well as to predict and optimize the best conditions to reduce the effect of protein nucleation.

Results

In this manuscript, experimental data of insulin, Aβ42 amyloid protein and apomyoglobin fibrillation from recent bibliography were selected to evaluate the capability of a bivariate sigmoid equation to model them. The mathematical functions (logistic combined with Weibull equation) were used in reparameterized form and the effect of inhibitor concentrations on kinetic parameters from logistic equation were perfectly defined and explained. The surfaces of data were accurately described by proposed model and the presented analysis characterized the inhibitory influence on the protein aggregation by several chemicals. Discrimination between true and apparent inhibitors was also confirmed by the bivariate equation. EGCG for insulin (working at pH = 7.4/T = 37°C) and taiwaniaflavone for Aβ42 were the compounds studied that shown the greatest inhibition capacity.

Conclusions

An accurate, simple and effective model to investigate the inhibition of chemicals on amyloid protein aggregation has been developed. The equation could be useful for the clear quantification of inhibitor potential of chemicals and rigorous comparison among them.

Effects of spill-treating agents on growth kinetics of marine microalgae

The effects of four spill-treating agents (STAs) (CytoSol, Finasol(®) OSR 51, Agma OSD 569 and OD4000) on the growth kinetics of three marine microalgae (Isochrysis galbana, Chaetoceros gracilis, Phaeodactylum tricornutum) were studied. Chlorophyll a concentration and optical density at 700 nm were assessed to describe the logistic growth of algae in batch cultures. The optical density data were initially analyzed as described for standard algal growth inhibition tests and subsequently modelled by a bivariate model, as a function of time and dose, to assess the toxic effects on growth parameters. Increasing trends in EC50 and EC10 values with time were found with the standard approach. In 8 of the 11 tests, the lag phase (λ) or the time required to achieve half the maximum biomass (τ) was significantly dependent on the STA concentration. A global parameter (EC50,τ) was calculated to summarize the effects of STAs on growth parameters in the bivariate model. The ranking of sensitivity as EC50,τ values was I. galbana>C. gracilis>P. tricornutum. For all species tested, the least toxic agent was Agma OSD 569, followed by CytoSol. The mathematical model allowed successful ecotoxicological evaluation of chemicals on microalgal growth.

Breed effect between Mos rooster (Galician indigenous breed) and Sasso T-44 line and finishing feed effect of commercial fodder or corn

The aim of this research was to study the Mos rooster breed growth performance, carcass, and meat quality. The breed effect (Mos vs. Sasso T-44) and finishing feed in the last month (fodder vs. corn) on animal growth, carcass characteristics, meat quality, and fatty and amino acid profiles were studied using a randomized block design with initial weight as covariance. In total, 80 roosters (n = 30 of Sasso T-44 line and n = 50 of Mos breed) were used. They were separated by breed and allocated to 2 feeding treatment groups (concentrate and corn). Each feeding treatment group consisted of 15 and 25 roosters, for Sasso T-44 line and Mos breed, respectively. Finishing feeding did not affect growth parameters in the 2 genotypes of rooster tested (P > 0.05). Nonetheless, the comparison between both types of roosters led to significant differences in growth parameters (P < 0.05). Regarding carcass characteristics, no significant influences of finishing feeding treatment (P > 0.05) were found, and as expected, carcass weight clearly differed between genotypes due to the lower growth rate of Mos roosters. However, drumstick, thigh, and wing percentages were greater in the Mos breed than in the hybrid line. In color instrumental traits, roosters feeding with corn showed breast meat with significantly (P < 0.001) higher a* and b* values than those of cocks feeding with commercial fodder. Values of shear force were less than 2 kg for both genotypes, thus it can be classified as very tender meat. Finishing with corn significantly increased (P < 0.001) the polyunsaturated fatty acid content in the breast; the Mos breed had a polyunsaturated to saturated fatty acid ratio of 0.73. The amino acid profile of the indigenous breed was not similar to that of the commercial strain. Finishing feeding treatment had a greater influence than breed effect on amino acid profile.