Mateusz Szala

Adsorption Studies of the Gram-Negative Bacteria onto Nanostructured Silicon Carbide

In this study, we demonstrated a significant adsorption of Pseudomonas putida bacteria onto aggregates of nanofibers (NFSiC) and nanorods (NRSiC) of silicon carbide (SiC) in aqueous suspensions. Langmuir and Freundlich isotherms were used to quantify adsorption affinities. It was found that adsorption of the bacteria strongly depended on the structure of the silicon carbide and the pH of the aqueous solution, which affected the isoelectric point of both the silicon carbide and the bacterial cells. The strongest affinity of bacteria was noted in the case of NRSiC aggregates. Affinity was inversely proportional to pH. Similarly, the adsorption of bacteria to the surface of the aggregates increased with decreasing pH. For NFSiC, the affinity of the bacteria for the surface of the aggregates was also inversely proportional to pH. However, adsorption increased at higher pH values. This discrepancy was explained by microscopic analysis, which showed that the bacterial cells were both adsorbed onto and trapped by NFSiC. The adsorption of bacteria onto a micrometric silicon carbide reference material was significantly smaller than adsorption onto nanostructured SiC.

Toxicity assessment of SiC nanofibers and nanorods against bacteria

In the present study, evidence of the antibacterial effects of silicon carbide (SiC) nanofibers (NFSiC) and nanorods (NRSiC) obtained by combustion synthesis has been presented. It has been shown that the examined bacteria, Pseudomonas putida, could bind to the surface of the investigated SiC nanostructures. The results of respiration measurements, dehydrogenase activity measurements, and evaluation of viable bacteria after incubation with NFSiC and NRSiC demonstrated that the nanostructures of SiC affect the growth and activity of the bacteria examined. The direct count of bacteria stained with propidium iodide after incubation with SiC nanostructures revealed that the loss of cell membrane integrity could be one of the main effects leading to the death of the bacteria.

Influence of 1,2,4,5-tetrazine derivatives on growth of bacterial consortium isolated from soil

This article presents the results of laboratory studies of the influence of tetrazine derivatives on the growth kinetic parameters of soil bacteria. 3,6-Dihydrazinotetrazine (DHTz), 3,6- bis(3,5-dimethylpyrazol-1-yl)-dihydro-1,2,4,5-tetrazine (DMPDHT) and N,N′-bis(1,2,4,5-tetrazine-6-(3,5-dimethylpirazylo))hydrazine (BDMPT) were applied. 3,6-Dihydrazinetetrazine had the largest influence on the growth of bacteria, reflected in a significant lengthening of the lag-phase and a decrease in the specific growth rate. Dehydrogenase activity was also determined in bacterial cultures exposed to tetrazine derivatives. Dehydrogenases remained active even at DHTz concentrations of 80 mg · L−1, which completely inhibited bacterial growth. The compounds studied variously influence the kinetics of growth in the bacterial consortium; at the same time, they undergo biodegradation in soil by autochthonous microflora.

Adsorption studies of azotetrazolate and 3,6-dihydrazinotetrazine on peat.

The objective of our studies was the evaluation of the adsorption process of two high-nitrogen compounds–dihydrazinotetrazine (DHTz) and azotetrazolate ion (AZ)−on a chosen peat. The experiments were performed using a static method at three different temperatures (283, 298, and 333 K). The adsorption process of DHTz and AZ on peat was characterized by isotherms according to the Freundlich and Langmuir models. The obtained correlations between adsorption and equilibrium concentration were in good accordance with the Freundlich and Langmuir models, as confirmed by high values of the correlation coefficients (0.97−0.99). Adsorption of AZ on peat was less efficient than that of DHTz, and this inference was experimentally proven. The maximum surface coverages of peat particles with adsorbate according to the Langmuir model were calculated as 0.02 and 0.17 mol kg−1 (at 298 K) for AZ and DHTz, respectively. The determined adsorption equilibrium constants confirmed greater adsorption of DHTz on the investigated peat. It can be concluded that adsorption of AZ occurred to a much lesser extent compared to that of DHTz, pointing to a potentially greater threat of migration of soluble azotetrazolates in soil. Standard enthalpies of adsorption estimated for AZ and DHTz were −11.1 and −23.7 kJ mol−1, respectively. Based on these adsorption enthalpy values, it can be stated that both investigated compounds are adsorbed on peat by a physisorption process.

Interaction of Gram-Positive and Gram-Negative Bacteria with Ceramic Nanomaterials Obtained by Combustion Synthesis – Adsorption and Cytotoxicity Studies

This paper presents the interactions of Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas putida) bacteria with ceramic materials obtained by combustion synthesis. These studies were conducted based on an analysis of the adsorption of bacteria onto aggregates of ceramic materials in an aqueous suspension. The materials used in the studies were of a nanostructured nature and consisted mainly of carbides: silicon carbide (SiC) in the form of nanofibers (NFs) and nanorods (NRs), titanium carbide, and graphite, which can also be formed by combustion synthesis. Micrometric SiC was used as a reference material. Gram-positive bacteria adsorbed more strongly to these materials. It seems that both the point of zero charge value and the texture of the ceramic material affected the bacterial adsorption process. Additionally, the viability of bacteria adsorbed onto aggregates of the materials decreased. Generally, P. putida cells were more sensitive to the nanomaterials than S. aureus cells. The maximum loss of viability was noted in the case of bacteria adsorbed onto NRSiC and NFSiC aggregates.

Oxidative stress in bacteria (Pseudomonas putida) exposed to nanostructures of silicon carbide

Silicon carbide (SiC) nanostructures produced by combustion synthesis can cause oxidative stress in the bacterium Pseudomonas putida. The results of this study showed that SiC nanostructures damaged the cell membrane, which can lead to oxidative stress in living cells and to the loss of cell viability. As a reference, micrometric SiC was also used, which did not exhibit toxicity toward cells. Oxidative stress was studied by analyzing the activity of peroxidases, and the expression of the glucose-6-phosphate dehydrogenase gene (zwf1) using real-time PCR and northern blot techniques. Damage to nucleic acid was studied by isolating and hydrolyzing plasmids with the formamidopyrimidine [fapy]-DNA glycosylase (also known as 8-oxoguanine DNA glycosylase) (Fpg), which is able to detect damaged DNA. The level of viable microbial cells was investigated by propidium iodide and acridine orange staining.

Toxic effect assessment of aminotetrazoles and high-energetic azotetrazole salts on soil microbial respiration

The influence of energetic heterocyclic high-nitrogen salts on microbial activity in soil enrichment was investigated. 5-Aminotetrazole, a sodium salt of 5-aminotetrazole, ammonium azotetrazolate, sodium azotetrazolate, guanidinium azotetrazolate, triaminoguanidine azotetrazolate and triaminoguanidine hydrochloride were examined. Respiration tests determined the amount and rate of production of CO2, H2 and H2S from microbial activity. Aminotetrazoles, triaminoguanidine azotetrazolate and triaminoguanidine hydrochloride substantially reduced the amount and rate of microbial CO2 production. The total amount of CO2 produced in the soil enrichments was affected by the cation from the azotetrazole salt, whereas the azotetrazolate anion did not seem to inhibit microbial CO2 production. In contrast, all applied compounds stopped the production of H2S completely and modified the rate of H2 production in the cultures compared with the control. The influence of ammonium azotetrazolate and sodium azotetrazolate on the activity of isolated sulfate-reducing bacteria was also determined. The compounds did not have bactericidal activity towards sulfate-reducing bacteria, but the compounds decreased the amount of H2S produced or slowed the growth of these bacteria in comparison with the control.

Synthesis of SiC/Ag/Cellulose Nanocomposite and Its Antibacterial Activity by Reactive Oxygen Species Generation

We describe the synthesis of nanocomposites, based on nanofibers of silicon carbide, silver nanoparticles, and cellulose. Silver nanoparticle synthesis was achieved with chemical reduction using hydrazine by adding two different surfactants to obtain a nanocomposite with silver nanoparticles of different diameters. Determination of antibacterial activity was based on respiration tests. Enzymatic analysis indicates oxidative stress, and viability testing was conducted using an epifluorescence microscope. Strong bactericidal activity of nanocomposites was found against bacteria Escherichia coli and Bacillus cereus, which were used in the study as typical Gram-negative and Gram-positive bacteria, respectively. It is assumed that reactive oxygen species generation was responsible for the observed antibacterial effect of the investigated materials. Due to the properties of silicon carbide nanofiber, the obtained nanocomposite may have potential use in technology related to water and air purification. Cellulose addition prevented silver nanoparticle release and probably enhanced bacterial adsorption onto aggregates of the nanocomposite material.