Development of Cellular and Enzymatic Bioluminescent Assay Systems to Study Low-Dose Effects of Thorium

Thorium is one of the most widespread radioactive elements in natural ecosystems, along with uranium, it is the most important source of nuclear energy. However, the effects of thorium on living organisms have not been thoroughly studied. Marine luminescent bacteria and their enzymes are optimal bioassays for studying low-dose thorium exposures. Luminescent bioassays provide a quantitative measure of toxicity and are characterized by high rates, sensitivity, and simplicity. It is known that the metabolic activity of bacteria is associated with the production of reactive oxygen species (ROS). We studied the effects of thorium-232 (10−11–10−3 M) on Photobacterium phosphoreum and bacterial enzymatic reactions; kinetics of bacterial bioluminescence and ROS content were investigated in both systems. Bioluminescence activation was revealed under low-dose exposures (<0.1 Gy) and discussed in terms of “radiation hormesis”. The activation was accompanied by an intensification of the oxidation of a low-molecular reducer, NADH, during the enzymatic processes. Negative correlations were found between the intensity of bioluminescence and the content of ROS in bacteria and enzyme systems; an active role of ROS in the low-dose activation by thorium was discussed. The results contribute to radioecological potential of bioluminescence techniques adapted to study low-intensity radioactive exposures.

Effect of Non-thermal Atmospheric Plasma on Viability and Histamine-Producing Activity of Psychotrophic Bacteria in Mackerel Fillets

Non-thermal atmospheric plasma (NTAP) has gained attention as a decontamination and shelf-life extension technology. In this study its effect on psychrotrophic histamine-producing bacteria (HPB) and histamine formation in fish stored at 0–5°C was evaluated. Mackerel filets were artificially inoculated with Morganella psychrotolerans and Photobacterium phosphoreum and exposed to NTAP to evaluate its effect on their viability and the histidine decarboxylase (HDC) activity in broth cultures and the accumulation of histamine in fish samples, stored on melting ice or at fridge temperature (5°C). NTAP treatment was made under wet conditions for 30 min, using a dielectric barrier discharge (DBD) reactor. The voltage output was characterized by a peak-to-peak value of 13.8 kV (fundamental frequency around 12.7 KHz). This treatment resulted in a significant reduction of the number of M. psychrotolerans and P. phosphoreum (≈3 log cfu/cm2) on skin samples that have been prewashed with surfactant (SDS) or SDS and lactic acid. A marked reduction of their histamine-producing potential was also observed in HDC broth incubated at either 20 or 5°C. Lower accumulation of histamine was observed in NTAP-treated mackerel filets that have been inoculated with M. psychrotolerans or P. phosphoreum and pre-washed with either normal saline or SDS solution (0.05% w/v) and stored at 5°C for 10 days. Mean histamine level in treated and control groups for the samples inoculated with either M. psychrotolerans or P. phosphoreum (≈5 log cfu/g) varied from 7 to 32 and from 49 to 66 μg/g, respectively. No synergistic effect of SDS was observed in the challenge test on meat samples. Any detectable amount of histamine was produced in the meat samples held at melting ice temperature (0–2°C) for 7 days. The effects of NTAP on the quality properties of mackerel’s filets were negligible, whereas its effect on the psychrotrophic HPB might be useful when time and environmental conditions are challenging for the cool-keeping capacity throughout the transport/storage period.

The impact of high-pressure processing on the growth of Photobacterium phosphoreum and biogenic amine formation in marinated herring

The effects of high-pressure processing (HPP) on Photobacterium phosphoreum growth and biogenic amine formation were evaluated in marinated herring (prepared with 2% acetic acid+8% NaCl; or 4% acetic acid+8% NaCl solutions). Marinated fish fillets were inoculated with P. phosphoreum, vaccum packaged and treated with HPP in different pressure levels (100, 300, and 500 MPa) and pressure holding times (5 and 10 min). Control was left as untreated for both marination group. All batches were stored at 4±1oC up to 3 months. The results showed that combined effect of HPP and 4% acetic acid had much more inhibitory effect on the growth of P. phosphoreum, especially pressure levels 300 and 500 MPa. During the storage period, H2S-producing bacteria growth was not observed in the groups subjected to 500 MPa pressure. Total psychrophilic bacteria did not grow in 500 MPa pressure treated group and 300 MPa 10 min pressure treated group prepared with 2% acetic acid during the storage period. Histamine was detected insignificant levels in the fillets marinated with 4% acetic acid and treated with HPP. Except for the control group tyramine formation was not found in the samples prepared with 4% acetic acid. Similarly, putrescine was not found in the samples prepared with 2% acetic acid and subjected to HPP treatment at the beginning of the storage. Cadaverine levels were found insignificant amount and 300 and 500 MPa pressure treatments suppressed the formation in 4% acetic acid treated groups compared with 2% acetic acid treated groups. The results of this study revealed that HPP in combination with 4% acetic acid had inhibitory effect on P. phosphoreum growth and suppressed the formation of histamine, tyramine, putrescine and cadaverine.

Antibacterial Potential Chloroform Extract of Photobacterium phosphoreum Bacteria Symbiotic in Light Organs of Squid Loligo duvauceli

Microorganisms that live in association with marine invertebrates are able to produce a compound similar to those produced by marine invertebrates and are thought to be potential as bioactive materials. Supplement extracts from the Photobacterium phosphoreum bacterial culture have been shown to have antibacterial activity. The purpose of this study was to determine the anti-bacterial activity of the chloroform extract of Photobacterium phosphoreum biomass against pathogenic bacteria Bacillus substilis, Staphylococcus aureus, Salmonella sp. and Escherichia coli. The extraction process was carried out by the liquid-liquid extraction method. Fractionation was performed using Open Column Chromatography (KKT). The antibacterial activity test was conducted by the agar diffusion method according to Kirby-Bauer. The results showed that for the antibacterial activity test of crude extract, the largest inhibition zone diameter occurred in Escherichia coli with a concentration of 50 µg / disk at 24 h incubation, namely (9.80 ± 0.75 mm), while the smallest inhibition zone diameter occurred in Salmonella sp. by giving a concentration of 10 µg / disk at an incubation time of 48 hours, namely (6.03 ± 0.05) mm. Of the 6 fractions resulting from crude extract fractionation, it was known that fraction 5 was the most active fraction and inhibited the growth of the tested bacteria. The largest inhibition zone diameter occurred in Escherichia coli (9.83 ± 0.28) mm, while the smallest inhibition zone diameter occurred in Salmonella sp. (8.63 ± 0.20 mm)

Metal Nanoparticles for Improving Bactericide Functionality of Usual Fibers

A wide variety of microbiological hazards stimulates a constant development of new protective materials against them. For that, the application of some nanomaterials seems to be very promising. Modification of usual fibers with different metal nanoparticles was successfully illustrated in the work. Tantal nanoparticles have shown the highest antibacterial potency within fibrous materials against both gram-positive (Bacillus subtilis) and gram-negative (Escherichia coli) bacteria. Besides, the effect of tantal nanoparticles towards luminescent Photobacterium phosphoreum cells estimating the general sample ecotoxicity was issued for the first time.