Ultraviolet irradiation of soil samples as a model of the effect of stress factors on bacterial diversity in soil ecosystem

UV irradiation is proposed for use in studying the effect of radioactive irradiation, since radioresistant bacteria are, as a rule, resistant to UV, and the mechanisms of repair of cell damage induced by UV and ionizing radiation are similar. It was found that the total number of bacteria and the number of dominant species in soil samples exposed to UV radiation decreased, indicating the unfavorable effect of UV radiation on bacterial diversity in soil ecosystems. The percentage of cells of bacteria belonging to dominant species varied significantly depending on the intensity of UV irradiation. It can be inferred that long-term irradiation of soils must impair the stability of soil ecosystems, a phenomenon that was indeed observed in the zone around the Chernobyl Nuclear Power Plant. At the same time, the UV irradiation of soil samples made it possible to reveal minor species, primarily UV-resistant pigmented bacteria. UV irradiation can probably be used as a selective factor for the isolation of radioresistant species.     

Growth of legionella and other heterotrophic bacteria in a circulating cooling water system exposed to ultraviolet irradiation

The effect of ultraviolet irradiation on the growth and occurrence of legionella and other heterotrophic bacteria in a circulating cooling water system was studied. Water of the reservoir was circulated once in 28 h through a side-stream open channel u.v. radiator consisting of two lamps. Viable counts of legionellas and heterotrophic bacteria in water immediately after the u.v. treatment were 0—12 and 0·7—1·2% of those in the reservoir, respectively. U.v. irradiation increased the concentration of easily assimilable organic carbon. In the u.v. irradiated water samples incubated in the laboratory the viable counts of heterotrophic bacteria reached the counts in reservoir water within 5 d. The increase in viable counts was mainly due to reactivation of bacterialcells damaged by u.v. light, not because of bacterial multiplication. Despite u.v. irradiation the bacterial numbers in the reservoir water, including legionellas, did not decrease during the experimental period of 33 d. The main growth of bacteria in the reservoir occurred in biofilm and sediment, which were never exposed to u.v. irradiation.     

Effect of ionizing radiation of the antigenic composition of typhoid bacteria

Changes in the antigenic composition of typhoid bacteria occurring during the exposure of microbial suspension to different doses of gamma irradiation [Co60] ranging between 0.5 and 3.0 Mrad were studied. Immunoelectrophoresis in agar was used to determine the antigenic composition of different samples of irradiated bacteria. The antigenic composition of bacteria irradiated with doses up to 2.5 Mrad was found to be similar to that of non-irradiated bacteria. Antigens demonstrated by means of Vi, H and O ontisera are preserved in these bacteria. However, all irradiated bacteria in general slightly differ from non-irradiated bacteria; this is manifest in a different configuration and position of the precipitation lines in the cathodic part of the immunophoreograms. The content of the component migrating rapidly towards the cathode, evidently the O antigen in the R form, in the irradiated bacteria increases with the dose of radiation. No new serologically active substances, non-existent in non-irradiated bacteria, were found to appear in the process of irradiation.     

Airborne enteric bacteria and viruses from spray irrigation with wastewater.

The relationship between bacterial concentrations in wastewater used for spray irrigation and in the air was examined. Aerosolized coliforms were detected when their concentration was 10(3)/ml or more in the wastewater. Relative humidity and solar irradiation appeared to affect viable bacteria in the air; a positive correlation was found between relative humidity and the number of aerosolized bacteria. The correlation between solar irradiation and bacterial level, on the other hand, was negative. During night irrigation, up to 10 times more aerosolized bacteria were detected than with day irrigation. Wind velocity did not play an important role in the survival of aerosolized bacteria. Echovirus 7 was isolated in 4 out of 12 air samples collected 40 m downwind from the sprinkler.     

Airborne enteric bacteria and viruses from spray irrigation with wastewater.

The relationship between bacterial concentrations in wastewater used for spray irrigation and in the air was examined. Aerosolized coliforms were detected when their concentration was 10(3)/ml or more in the wastewater. Relative humidity and solar irradiation appeared to affect viable bacteria in the air; a positive correlation was found between relative humidity and the number of aerosolized bacteria. The correlation between solar irradiation and bacterial level, on the other hand, was negative. During night irrigation, up to 10 times more aerosolized bacteria were detected than with day irrigation. Wind velocity did not play an important role in the survival of aerosolized bacteria. Echovirus 7 was isolated in 4 out of 12 air samples collected 40 m downwind from the sprinkler.     

Modification of radiation damage of bacteria by folic acid antagonists

Pittillo, Robert F. (Southern Research Institute, Birmingham, Ala.), Mary Lucas, Robert T. Blackwell, and Carolyn Woolley. Modification of radiation damage of bacteria by folic acid antagonists. J. Bacteriol. 90:1548-1551. 1965.-The folic acid analogues, 2,4-diamino-6-methylpteridine, amethopterin, and aminopterin, have been found to sensitize certain bacteria, especially Escherichia coli, to the lethal action of ionizing irradiation. Data are presented which indicate that (i) the compounds must be present during the irradiation period for maximal sensitization to be observed, (ii) the sensitizing effect can be nullified by cysteine or cysteamine, (iii) the sensitizing effect occurs in a number of diverse bacterial genera, and (iv) folic acid neither sensitizes bacteria to irradiation nor prevents the sensitization caused by these antifolic agents.     

Development of light-shielding hydrogel for nitrifying bacteria to prevent photoinhibition under strong light irradiation

Microalgae-nitrifying bacteria consortia have gained attention because photooxygenation of algae can supply oxygen to bacteria which eliminates the need for costly mechanical aeration. However, nitrifying bacteria are known to suffer from photoinhibition. In this study, we developed “Light-shielding hydrogel”, in which bacteria were immobilized in hydrogel and light-shielding particles (carbon black) were incorporated, and evaluated its effectiveness to mitigate photoinhibition for bacteria under strong light irradiation. For comparison, “Hydrogel”, in which bacteria were immobilized in hydrogel without carbon black, and “Dispersion” which was simply suspended bacteria were prepared. At 1600 μmol photons m⁻² s^–1, the nitrification performance markedly decreased to 15.1 and 48.0% compared to the dark condition in the Dispersion and the Hydrogel, respectively. Meanwhile, it was successfully maintained for the Light-shielding hydrogel. Our results showed that the effectiveness of light-shielding hydrogel to mitigate photoinhibition on nitrifying bacteria even under strong light irradiation.     

The effect of combinations of irradiation and pH on the survival of Escherichia coli on chicken meat

The effect of combinations of electron beam irradiation and pH on survival of Escherichia coli NCIMB 9270 on chicken breast meat was studied using two methods. Bacteria were added directly to pH-modified meat or supported on membrane filters on the surface of pH-modified meat. In the absence of irradiation. pH variation between 3.7 and 5.8 had no effect on the survival of E. coli. Irradiation of 2 kGy gave a 3–4 log cycle reduction of bacteria on meat and a 4–5 log cycle reduction of bacteria on membrane filters. With both methods and at all pH values there was a pronounced tailing effect with increasing doses of irradiation.     

Inhibition of bacterial attachment by pulsed Nd:YAG laser irradiations: an in vitro study using marine biofilm-forming bacterium Pseudoalteromonas carrageenovora

The effect of low mean power laser irradiations with short pulse duration from an Nd:YAG (neodymium-doped yttrium aluminium garnet) laser on a marine biofilm-forming bacterium, Pseudoalteromonas carrageenovora, was investigated in the laboratory. Laser-irradiated bacteria were tested for their ability to attach on nontoxic titanium nitride (TiN) coupons with nonirradiated bacteria as the reference. Two durations of irradiation were tested, 10 and 15 min. Bacterial attachment was monitored after 20 min, 40 min, and 1 h of irradiation. The average laser fluence used for this study was 0.1 J/cm(2). The area of attachment of the irradiated bacteria was significantly less than the reference for both durations of irradiation. The growth of irradiated bacteria showed a longer lag phase than the nonirradiated sample, mainly due to mortality in the former. The bacterial mortality observed was 23.4 +/- 0.71 and 48.6 +/- 6.5% for 10- and 15-min irradiations, respectively. Thus, the results show that low-power pulsed laser irradiations resulted in a significant bacterial mortality and a reduced bacterial attachment on nontoxic hard surfaces.     

Ultraviolet reactivation of lambda phage: assay of infectivity of DNA molecules by spheroplast transfection

Prior irradiation of non-lysogenic bacteria by ultraviolet light leads to an increase in the viability of infecting irradiated λ phage (ultraviolet reactivation). Similarly, u.v. irradiation of wild type or uvrD bacteria lysogenic for λcIind^? increased the fraction of closed circular duplex phage DNA molecules formed after infection with u.v.-irradiated λ phage. The closed circular molecules isolated from the irradiated lysogens were shown to be free from u.v. damage by a spheroplast transfection assay. The increase of closed circular molecules is sufficient to explain the ultraviolet reactivation observed by the increase of viability of irradiated phage.In ultraviolet reactivation, damage must be erased on irradiated DNA molecules and the repair is independent of total replication of phage genomes, exchange of sister chromatids or recombination between phage genomes. Protein synthesis is necessary to increase the level of closed circular molecules of irradiated λ phage after irradiation of bacteria.     

Repair and recombination of nonreplicating UV-irradiated phage DNA in E. coli III. Enhancement of excision repair in UV-treated bacteria

Summary The question of whether induction of the SOS response in Escherichia coli increases the efficiency of excision repair was addressed by measuring repair of UV-damaged nonreplicating lambda phage DNA in previously irradiated bacteria. Prior UV irradiation of lex ⁺ bacteria enhanced both the rate of regeneration of infective phage DNA (about 10-fold) and the rate of cyclobutane dimer removal early in repressed infections. Indirect induction of SOS-regulated repair activities by the nonreplicating irradiated phage DNA itself seemed negligible. Prior bacterial irradiation reduced the frequency of recombination (loss of a tandem chromosomal duplication) of nonreplicating UV-irradiated DNA. In this respect UV-stimulated recombination of nonreplicating DNA differs from RecF-dependent recombination processes that are stimulated by increased SOS expression.Surprisingly, prior UV irradiation of lexA3 bacteria caused a small but reproducible increase in the regeneration of infective phage DNA.     

Studies on radiation-sensitive mutants of E. coli. 3. Participation of the rec system in induction of mutation by ultraviolet irradiation

Summary The bacterial recA gene participates in the induction by UV irradiation of the clear mutation of phage and the Lac^- mutation of bacteria. The necessary function is induced by irradiation of Rec⁺ bacteria and acts upon DNA irradiated with UV light.     

The effects of electromagnetic radiation of extremely high frequency and low intensity on the growth rate of bacteria Escherichia coli and the role of medium pH

It has been shown that coherent electromagnetic irradiation (EMI) of extremely high frequency (45-53 GHz) or millimeter waves (wavelength 5.6-6.7 mm) of low intensity (flux capacity 0.06 mW/cm2) of Escherichia coli K12, grown under anaerobic conditions during the fermentation of sugar (glucose) for 30 min or 1 h, caused a decrease in their growth rate, the maximum inhibitory effect being achieved at a frequency of 51.8 or 53 GHz. This effect depended on medium pH when the maximal action was determined at pH 7.5. In addition, separate 30-min of 1-h irradiation (frequency 51.8 or 53 GHz) of doubly distilled water or some inorganic ions contained in Tris-phosphate buffer where the cells were transferred induced oppositely directed changes in further growth of these bacteria under anaerobic conditions; irradiation of water caused a decrease in the growth rate of bacteria. A significant change in pH of water (0.5-1.5 unit) was induced by a 30-irradiation at a frequency of 49, 50.3, 51.8, or 53 GHz, when the initial pH value was 6.0 or 8.0, but not 7.5. These results indicate the changes in the properties of water and its role in the effects of EMI of extremely high frequency. The marked effect of EMI on bacteria disappeared upon repeated irradiation for 1 h at a frequency of 51.8 or 53 GHz with an interval of 2 hours. This result indicates some compensatory mechanisms in bacteria.     

Overproduction of single-stranded-DNA-binding protein specifically inhibits recombination of UV-irradiated bacteriophage DNA in Escherichia coli.

Overproduction of single-stranded DNA (ssDNA)-binding protein (SSB) in uvr Escherichia coli mutants results in a wide range of altered phenotypes. (i) Cell survival after UV irradiation is decreased; (ii) expression of the recA-lexA regulon is slightly reduced after UV irradiation, whereas it is increased without irradiation; and (iii) recombination of UV-damaged lambda DNA is inhibited, whereas recombination of nonirradiated DNA is unaffected. These results are consistent with the idea that in UV-damaged bacteria, SSB is first required to allow the formation of short complexes of RecA protein and ssDNA that mediate cleavage of the LexA protein. However, in a second stage, SSB should be displaced from ssDNA to permit the production of longer RecA-ssDNA nucleoprotein filaments that are required for strand pairing and, hence, recombinational repair. Since bacteria overproducing SSB appear identical in physiological respects to recF mutant bacteria, it is suggested that the RecF protein (alone or with other proteins of the RecF pathway) may help RecA protein to release SSB from ssDNA.     

Indirect and repeated electromagnetic irradiation of extremely high freguency of bacteria Escherichia coli

It has been shown that separate irradiation of distilled water and tris-phosphate buffer containing some inorganic ions, with Escherichia coli K12 grown in anaerobic conditions upon fermentation of sugar (glucose) with "noise" electromagnetic radiation of extremely high frequencies (53.5-68 gHz) or millimeter waves (wavelength of 3 to 8 mm) with low flux capacity (0.01 mW) for 10, 30 and 60 min caused opposite effects, changing the growth of these bacteria. The irradiation of water has a bactericide effect, whereas the irradiation of the buffer stimulates bacterial growth although the buffer itself inhibits the growth. These results point out the role of water in the bactericide action of "noise" electromagnetic radiation of extremely high frequencies, and confirm the significance of membranotropic effects. The bactericide action disappeared after repeated irradiation for 10 and 30 min with 2-h intervals. This indicates the operation of some compensatory mechanisms in bacteria.     

New water disinfection system using UVA light-emitting diodes

AIM: To evaluate the ability of high-energy ultraviolet A (UVA) light-emitting diode (LED) to inactivate bacteria in water and investigate the inactivating mechanism of UVA irradiation. METHODS AND RESULTS: We developed a new disinfection device equipped with high-energy UVA-LED. Inactivation of bacteria was determined by colony-forming assay. Vibrio parahaemolyticus, enteropathogenic Escherichia coli, Staphylococcus aureus and Escherichia coli DH5alpha were reduced by greater than 5-log(10) stages within 75 min at 315 J cm(-2) of UVA. Salmonella enteritidis was reduced greater than 4-log(10) stages within 160 min at 672 J cm(-2) of UVA. The formation of 8-hydroxy-2'-deoxyguanosine in UVA-LED irradiated bacteria was 2.6-fold higher than that of UVC-irradiated bacteria at the same inactivation level. Addition of mannitol, a scavenger of hydroxyl radicals (OH(*)), or catalase, an enzyme scavenging hydrogen peroxide (H(2)O(2)) to bacterial suspensions significantly suppressed disinfection effect of UVA-LED. CONCLUSION: This disinfection system has enough ability to inactivate bacteria and OH(*) and H(2)O(2) participates in the disinfection mechanism of UVA irradiation. SIGNIFICANCE AND IMPACT OF THE STUDY: We newly developed UVA irradiation system and found that UVA alone was able to disinfect the water efficiently. This will become a useful disinfection system.     

Characteristics of Mesophilic Bacteria Isolated during Thermophilic Composting of Sewage Sludge

The degree of inactivation by UV irradiation was different between vegetative cells and spores of bacteria isolated from sewage sludge composting at 60°C. By using this property, a method to estimate the spore ratio of a mixture of vegetative cells and spores was presented. This UV irradiation method was applied to the estimation of the spore ratio of sewage sludge compost samples collected at several stages of composting. The spore ratio of mesophilic bacteria in the samples obtained at the thermophilic stage of 60°C was 40% at most. The vegetative form of mesophilic bacteria showed a thermotolerance property at 60°C by forming colonies but showed no respiratory activity at that temperature.     

The induction of mutants of Acinetobacter calcoaceticus NCIB8250 and their selection by Vancomycin.

The mutagenic and lethal effects of N-methyl-N-nitro-N-nitrosoguanidine (NTG), ethyl methanesulphonate (EMS), ultraviolet light iffadiation and near-ultraviolet light irradiation with 8-methoxypsoralen on the bacterium Acinetobacter calcoaceticus NCIB8250 were examined. The production of auxotrophic mutants was used as a measure of mutagenic efficiency. Under appropriate conditions all four agents were mutagenic. EMS and NTG although more effective than irradiation, did not cause such a high frequency of mutation as has been observed with other bacteria. A combination of vancomycin and penicillin V gave enrichment of non-metabolizing bacteria and optimum conditions were found for the use of these compounds in a selection technique.     

Effect of antimicrobial therapy on bowel flora and bacterial infection in irradiated mice

Mice exposed to 10 Gy cobalt-60 radiation were given intramuscular antimicrobial therapy of gentamicin, or metronidazole, or a combination of the two. Mortality in the mice treated with metronidazole alone or in combination with gentamicin occurred earlier than in the controls (P less than 0.001). Microorganisms were recovered from the blood, spleen, and liver of the metronidazole-treated mice earlier than from other groups. The predominant organisms recovered from these animals were Enterobacteriaceae. Quantitative cultures of the ileal flora showed a decrease in the number of aerobic, facultative anaerobic and strict anaerobic bacteria after irradiation, and a subsequent increase only in the number of strict aerobic bacteria. As compared to untreated mice, a rapid decrease (by 8.8 logs) in the number of anaerobic flora occurred in the mice treated with metronidazole 5 days after irradiation. This was followed by a rapid increase in the number of aerobic organisms which coincided with the earlier mortality in this group. These data suggest that antimicrobial agents that decrease the number of the strict anaerobic component of the gut flora enhance systemic infection by aerobic or facultative anaerobic bacteria, and this facilitates mortality after irradiation.     

Effect of temperature on dose-dependent changes in sedimentation characteristics of bacterial DNA produced, in vivo, by near-ultraviolet irradiation and 8-methoxypsoralen

Dose-dependent changes in the sedimentation characteristics of bacterial DNA are produced, in vivo, by near-ultraviolet irradiation in the presence of the photosensitizer, 8-methoxypsoralen. These changes are probably due to DNA cross links and are associated with both lethality and mutation induction in bacteria. Irradiation at low temperatures in the frozen state leads to increased cross linking, mutation induction, and lethality at irradiation temperatures between 0 and approximately ?50 ° C. At even lower irradiation temperatures (?130 to ?196 ° C) much larger amounts of energy are required to produce changes in DNA, lethality, and mutation induction. At ?196 ° C bacteria are very resistant to the biological effects of photosensitization and no cross linking of DNA is observed. However, a new pattern of DNA damage is apparent. Irradiation temperature thus affects both the nature and quantity of induced photoproduct and the biological consequences of such changes.