Lethal Effect Induced in Pseudomonas aeruglnosa Exposed to Ultraviolet-A Radiation

Ultraviolet-A (365 nm, 120 kJ/m²/h) exposure caused cell death in Pseudomonas aeruginosa at doses at which Escherichia coli cell viability was not affected. We have not found that UVA induced growth delay or any other sublethal effect. Irradiated suspensions of P. aeruginosa showed a marked reduction in membrane-bound succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) activities. Succinate-driven respiration and several nutrient transport systems were also inhibited. Whereas SDH and LDH activities were independent of the irradiation conditions, cell viability, respiration and transport systems were protected when irradiation was performed in an N₂ atmosphere. A similar protective effect was observed when cells were grown in media containing glycerol or when preirradiation bacterial growth was carried out at 30°C (instead of 37°C). Results suggest that UVA induces a differential damaging effect on several biochemical functions of P. aeruginosa. The UVA induced photodamage may fall into two categories: indirect damage mediated by oxygen (cell killing and inhibition of respiration and transport systems) and direct damage to SDH and LDH (apparently not oxygen dependent). These enzymes and leucine transport appear not to be involved in the lethal effect described herein because they were altered despite viability-preserving conditions.     

Growth ofschizosaccharomyces pombe on glucose-malte mixtures in continuous cell-recycle cultures kinetics of substrate utilization

The aerobic growth ofSchizosaccharomyces pombe on mixtures of glucose and malate was investigated during continuous high cell density cultures with partial cell-recycle using a membrane bioreactor. Determination of the specific metabolic rates relative to substrates and products allowed the capacity of the yeast to metabolize malic acid under both oxidative metabolism (carbon limited cultures) and oxidofermentative metabolism (carbon sufficient cultures) situations to be characterized. Under carbon limiting conditions, the specific rate of malate utilization was dependent on the residual concentration and a limit for a purely oxidative breakdown without ethanol formation was observed for a characteristic ratio between the rates of substrate consumption qm/qg of 1.63 g.g^-1. In addition, the mass balance analysis revealed the incorporation of malic acid into biomass. In carbon excess environments, the specific rate of malate utilization was dependent on both the residual malate and the specific rate of glucose consumption indicating that in addition to its conversion into ethanol malate can be respiratively metabolized for qm/qg ratios higher than 0.4 g.g^-1.     

Hexose transport regulation in cultured hamster cells

Hamster (nil) cells maintained overnight in culture medium containing cyclohemiximide and either glucose or fructose exhibit strikingly different rates of hexose transport and metabolism (i.e. uptake). Pretreatment of cultures with sulfhydryl reagents makes it possible to determine initial transport rates for a physiological sugar such as galactose which is a catabolite in hamster cells. Using galactose transport as a model, hexose uptake enhancements can now be shown to be due almost entirely to increases in the rate of the transport step. The transport regulation can best be accounted for by a model comprised of 2 antagonizing mechanism. This model involves turnover of transport carriers as well as inhibitory units ("regulators"). The experimental as well as the theoretical model may also apply to the well-known uptake enhancements observed in oncogenically transformed cells.     

Influence of redox potential on product distribution in Clostridium thermosuccinogenes

Clostridium thermosuccinogenes are the only known anaerobic thermophilic bacteria that ferment inulin to succinate and acetate as major products and formate, lactate, and ethanol as minor products. In this study, organic acid production in 2-L fermentations having an initially low (−300 to −330 mV) or high (−220 to −250 mV) redox potential was compared for two strains of C. thermosuccinogenes (DSM 5808 and DSM 5809). Although DSM 5809 consistently provided higher succinate yield, high variability in results was attributed to the absence of redox control during the fermentations, and, therefore, fermentations at three controlled redox potentials (−240, −275, and −310 mV) were conducted. At an intermediate redox potential (−275 mV), the succinate yield was the greatest (0.36 g of succinate/g of hexose unit), whereas ethanol yield was the least (0.02 g/g). Redox potential did not significantly affect acetate or lactate formation. At controlled redox potential of −275 mV, the growth of DSM 5809 on three substrates was also compared: inulin, fructose, and glucose. DSM 5809 had similar growth rates when inulin (0.20/h) or glucose (0.21/h) was the carbon source but grew more slowly when fructose (0.16/h) was the carbon source. Also, the specific rate of utilization of fructose by DSM 5809 was higher (0.89 g of fructose/[g of biomass·h]) compared to glucose (0.53 g/[g·h]) or inulin (0.55 g/[g·h]). Succinate was the major product formed by DSM 5809 fermenting inulin (0.50 g/[g·h]) or glucose (0.36 g/[g·h]), and ethanol was the principal product when DSM 5809 fermented fructose (0.54 g/[g·h]).     

MUTATIONAL INTERACTIONS BETWEEN NEAR-UV RADIATION AND DNA DAMAGING AGENTS IN Escherichia coli: THE ROLE OF NEAR-UV-INDUCED MODIFICATIONS IN GROWTH AND MACROMOLECULAR SYNTHESIS

Abstract— The mutational interactions between near-ultraviolet (near-UV, 334 nm, 365 nm) radiation and DNA damaging agents (far-UV (254 nm) and ethyl-methanesulphonate (EMS)) were studied in strains of Escherichia coli B/r trp thy with different susceptibilities to near-UV-induced growth delay (wild-type, rel and srd ). Far-UV induced reversion to tryptophan independence is reduced while forward mutation to streptomycin is enhanced by prior exposure of the rel+ srd+ strains to near-UV radiation. The observed interactions are reduced ( rel ) or absent ( srd ) in the two mutant strains as are the corresponding growth and macromolecular synthesis delays normally observed after near-UV treatment. Quantitatively, the degree of interaction induced by near-UV pre-treatment correlates closely with the degree of protein synthesis inhibition. We propose a mechanism for the contrasting interactions at the two genetic loci based on the different pathways by which pre-mutagenic lesions may be processed. The primary chromophore for the mutational interactions would appear to be 4-thiouracil-containing transfer RNA.     

Bildung von α-Mannosidase durch Arthrobacter

The production of yeast cell wall mannan degrading -mannosidase was studied in shake flask experiments as well as in a highly instrumented, computer-coupled bioreactor. The enzyme is predominantly excreted into the culture liquid upon submerged cultivation on yeast mannan. Only low activities were detected with mannose or glucose as carbon source whereas the enzyme formation was totally repressed by glycerol. The amount of enzyme produced is proportional to the microbial biomass formed.Carbon-unlimited cultivation on mannose, the primary product of enzymic digestion, resulted in a specific growth rate of 0.10h^–1, a specific oxygen uptake rate ·h and a respiratory quotient ofRQ=1.0. Addition of yeast mannan (0.5%) to nutrient-depleted bacterial cells resulted in an almost complete utilization of this substrate, with 55% of substrate carbon being converted to biomass and 37% to carbon dioxide. The yield coefficient on mannan wasY _x/s =0.51 (g/g). Enzyme formation started with a delay of 30–40 min and stopped with termination of growth. Due to the increased production of mannose by the action of the enzyme the specific growth rate increased from 0.05 to 0.10 h^–1, thus enabling computations of maintenance and yield coefficients for oxygen and carbon dioxide metabolism.

     

Comparative energetics of glucose and xylose metabolism in recombinant Zymomonas mobilis

Recombinant Zymomonas mobilis CP4:pZB5 was grown with pH control in batch and continuous modes with either glucose or xylose as the sole carbon and energy source. In batch cultures in which the ratio of the final cell mass concentration to the amount of sugar in the medium was constant (i.e., under conditions that promote “coupled growth”), maximum specific rates of glucose and xylose consumption were 8.5 and 2.1 g/(g of cell…h), respectively; maximum specific rates of ethanol production for glucose and xylose were 4.1 and 1.0 g/(g of cell…h), respectively; and average growth yields from glucose and xylose were 0.055 and 0.034 g of dry cell mass (DCM)/g of sugar respectively. The corresponding value of Y_ATP for glucose and xylose was 9.9 and 5.1 g of DCM/mol of ATP, respectively. Y_ATP for the wild-type culture CP4 with glucose was 10.4g of DCM/mol of ATP. For single substratechem ostat cultures in which the growth rate was varied as the dilution rate (D), the maximum or “true” growth yield (max Y_a/s) was calculated from Pirt plots as the inverse of the slope of the best-fit linear regression for the specific sugar utilization rate as a function of D, and the “maintenance coefficient” (m) was determined as the y-axis intercept. For xylose, values of max Y _s/s and m were 0.0417g of DCM/g of xylose (Y_ATP=6.25) and 0.04g of, xylose/(g of cell…h), respectively. However, with glucose there was an observed deviation from linearity, and the data in the Pirt plot was best fit with a second-order polynomial in D. At D>0.1/h, Y_ATP=8.71 and m=2.05g of glu/(g of cell…h) whereas at D<0.1/h, Y_ATP=4.9g of DCM/mol of ATP and m=0.04g of glu/(g of cell…h). This observation provides evidence to question the validity of the unstructured growth model and the assumption that Pirt's maintenance coefficient is a constant that is in dependent of the growth rate. Collectively, these observations with individual sugars and the values assign ed to various growth and fermentation parameters will be useful in the development of models to predict the behavior of rec Zm in mixed substrate fermentations of the type associated with biomass-to-ethanol processes.     

MEMBRANE DAMAGE AND RECOVERY ASSOCIATED WITH GROWTH DELAY INDUCED BY NEAR-UV RADIATION IN Escherichia coliK–12

Abstract— The growth delay induced by near-UV radiation has been largely attributed to injured tRNA's and to the stringent response. We report an associated membrane perturbation whose recovery determines substantial modifications in the behavior of log phase Escherichia coli K–12 exposed to sublethal doses of near-UV radiation (366 nm). When incubated at 37°C in plain nutrient broth, cells suffered a growth delay of about 100 min with parallel inhibition of several membrane functions. Conversely, when grown in conditions known to influence membrane activities, these were slightly inhibited and the growth delay lasted about 50 min. All the above conditions triggered the stringent response, characterized by an equivalent post-irradiation burst of intracellular guanosine 5'3' tetra and pentaphosphate and by a similar decay rate of the nucleotides accumulated at time 0 of the growth lag. According to our data the polyphosphates' half decay time in irradiated cells remains practically constant and close to 15 min. But, while cells from unsupplemented broth at 37°C resumed normal growth in around 100 min those with recovered membranes were rescued from growth inhibition in about one half of that time.     

Effects of potassium on the ethanol production rate of Saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation

The influence of potassium on ethanol production bySaccharomyces cerevisiae wild type and AR5 cells carrying the plasmid pCYG4 was investigated. This plasmid carries the glutamate dehydrogenase gene conferring an 11-fold higher level of expressed enzyme activity over the wild type cells. All experiments were carried out in batch culture with medium supplemented to different potassium concentrations up to 180 mM. Maximum ethanol production rate was observed in the AR5 cells grown in medium supplemented with 3.5 mM of potassium ions. Glucose uptake rate increased with increasing potassium up to 60 mM, but higher concentrations depressed glucose uptake rate in both strains. Furthermore, the wild type cells showed higher growth rate, ethanol production, and glucose consumption rate than the AR5 cells. These lower rates in the AR5 cells could be explained by repression of potassium uptake by an enhancement of ammonium feeding, and greater energy requirements by these cells due the presence of the plasmid.     

GROWTH DELAY STUDIES OF THE RESPONSE OF V-79 MULTICELL SPHEROIDS EXPOSED TO DHE and RED LIGHT

Abstract Multicell tumour spheroids (MTS) of V-79 Chinese hamster cells have been used to study the role of a number of treatment and microenvironmental parameters in the modification of tumour response to Photodynamic Therapy (PDT) using visible light in combination with the photosensitizing compound dihematoporphyrin ether (DHE). The kinetics of DHE uptake into MTS, determined by fluorimetry of extracted porphyrins, indicate that after extended incubation (i.e. 24 h) the mean cellular DHE content in larger (˜300 μ.m and 400 u.m) MTS is significantly less than that for smaller (˜200 μm) MTS, consistent with a hypothesis that DHE uptake into the internal regions of spheroids is diffusion-limited. The response of spheroids to PDT, as assessed by the endpoint of growth delay, indicates that the kinetics of spheroid volume alteration and cell loss, as well as the potential for regfrrwth, are markedly dependent on both the drug and light exposure levels used. The oxygen dependence of this response has been investigated after light irradiation of spheroid cultures equilibrated with either 21% O₂ (i.e. air) or 0% 0₂ (i.e. N₂). While treatment in air results in significant growth delay, the growth kinetics of DHE-treated spheroids irradiated under N₂ were essentially unchanged from those of untreated spheroids. These observations clearly demonstrate an important role for oxygen, at the time of irradiation, in determining the response of spheroids to PDT.     

GpdA-promoter-controlled production of glucose oxidase by recombinant aspergillus niger using nonglucose carbon sources

The gpdA-promoter-controlled exocellular production of glucose oxidase (GOD) by recombinant Aspergillus niger NRRL-3 (GOD3-18) during growth on glucose and nonglucose carbon sources was investigated. Screening of various carbon substrates in shake-flask cultures revealed that exocellular GOD activities were not only obtained on glucose but also during growth on mannose, fructose, and xylose. The performance of A. niger NRRL-3 (GOD3-18) using glucose, fructose, or xylose as carbon substrate was compared in more detail in bioreactor cultures. These studies revealed that gpdA-promoter-controlled GOD synthesis was strictly coupled to cell growth. The gpdA-promoter was most active during growth on glucose. However, the unfavorable rapid GOD-catalyzed transformation of glucose into gluconic acid, a carbon source not supporting further cell growth and GOD production, resulted in low biomass yields and, therefore, reduced the advantageous properties of glucose. The total (endo- and exocellular) specific GOD activities were lowest when growth occurred on fructose (only a third of the activity that was obtained on glucose), whereas utilization of xylose resulted in total specific GOD activities nearly as high as reached during growth on glucose. Also, the portion of GOD excreted into the culture fluid reached similar high levels (≅ 90%) by using either glucose or xylose as substrate, whereas growth on fructose resulted in a more pelleted morphology with more than half the total GOD activity retained in the fungal biomass. Finally, growth on xylose resulted in the highest biomass yield and, consequently, the highest total volumetric GOD activity. These results show that xylose is the most favorable carbon substrate for gpdA-promoter-controlled production of exocellular GOD.     

Effects of Oxygen Limitation on Xylose Fermentation, Intracellular Metabolites, and Key Enzymes of Neurospora crassa AS3.1602

The effects of oxygen limitation on xylose fermentation of Neurospora crassa AS3.1602 were studied using batch cultures. The maximum yield of ethanol was 0.34 g/g at oxygen transfer rate (OTR) of 8.4 mmol/L·h. The maximum yield of xylitol was 0.33 g/g at OTR of 5.1 mmol/L·h. Oxygen limitation greatly affected mycelia growth and xylitol and ethanol productions. The specific growth rate (μ) decreased 82% from 0.045 to 0.008 h⁻¹ when OTR changed from 12.6 to 8.4 mmol/L·h. Intracellular metabolites of the pentose phosphate pathway, glycolysis, and tricarboxylic acid cycle were determined at various OTRs. Concentrations of most intracellular metabolites decreased with the increase in oxygen limitation. Intracellular enzyme activities of xylose reductase, xylitol dehydrogenase, and xylulokinase, the first three enzymes in xylose metabolic pathway, decreased with the increase in oxygen limitation, resulting in the decreased xylose uptake rate. Under all tested conditions, transaldolase and transketolase activities always maintained at low levels, indicating a great control on xylose metabolism. The enzyme of glucose-6-phosphate dehydrogenase played a major role in NADPH regeneration, and its activity decreased remarkably with the increase in oxygen limitation.     

Model compound studies

The influence of other hemicellulosic sugars (arabinose, galactose, mannose, and glucose), oxygen limitation, and initial xylose concentration on the fermentation of xylose to xylitol was in vestigated using experimental design methodology. Oxygen limitation and initial xylose concentration had strong influences on xylitol production by Candida tropicalis ATCC 96745. Under semiaerobic conditions, xylitol yield was highest (0.62 g/g), whereas under aerobic conditions volumetric productivity was highest (0.90g/[L·h]). In the presence of glucose, xylose utilization was strongly repressed and sequential sugar utilization was observed. Ethanol produced from the glucose caused a 50% reduction in xylitol yield when the ethanol con centration exceeded 30 g/L. When complex synthetic hemicellulosic sugars were fermented, glucose was initially consumed followed by a simultaneous uptake of the other sugars. The highest xylitol yield (0.84 g/g) and volumetric productivity (0.49 g/[L·h]) were obtained for substrates containing high arabinose and low glucose and mannose contents.     

Theoretical approach to non-constant uptake rates for tube-type diffusive samplers

A simple theoretical model was developed for evaluating the validity of the simplified uptake model of diffusive sampling. In the model based on the plate theory diffusion to the adsorbent surface, phase equilibrium of the adsorbate and mass transport in the adsorbent bed were considered. It was found that in the early stage of sampling, the rate of sampling is close to its theoretical value. As sampling progresses, the concentration increases and the mass transfer front gradually moves into the adsorbent layer. Above a certain threshold limit, the mass uptake becomes a steady state process in which the diffusion in the air gap and the mass transport in the adsorbent bed are balanced. As uptake is a cumulative process, sampling should continue long enough to render the effects of these initial changes negligible. That is why constant uptake rates can still be obtained above a critical exposure dose. This critical exposure dose should be exceeded both in the determination of uptake rates and outdoor measurements, to obtain consistent and reliable analytical data. Evaluation of the time and concentration dependence of uptake rate in laboratory experiments and the time dependence of uptake rate in filed test was performed to justify the model results. Since the determination of uptake rates always takes places in the laboratory, where the exposure time is much shorter and the concentration is much higher than in the environment, the uptake rates are thus overestimated by 10-30%. Therefore, the uptake rates should be determined in the field under ambient conditions by means of an independent reference method.     

IN VIVO INDUCTION OF 4-THIOURIDINE-CYTIDINE ADDUCTS IN tRNA OF E. COLI B/r BY NEAR-ULTRAVIOLET RADIATION*

Abstract— Near-ultraviolet (near-UV; 320–405 nm) irradiation of Escherichia coli B/r induces the formation in vivo of ⁴Srd-Cyd adducts in transfer RNA, as evidenced by (1) fluorescence spectrum changes of tRNA extracted from irradiated cells and reduced with NaBH₄, (2) thin-layer chromatography on cellulose of hydrolysates of trichloroacetic acid-precipitable extracts of irradiated cells, and (3) comparison of these findings with adduct formation induced by near-UV irradiation of purified mixed tRNA from E. coli. The kinetics of induction of the ⁴Srd-Cyd adduct in vivo, and the near-UV fluences required, provide strong support for our earlier hypothesis that formation of these adducts is responsible for near-UV-induced growth delay in E. coli.     

EVIDENCE AGAINST DNA AS THE TARGET FOR 334 NM-INDUCED GROWTH DELAY IN ESCHERICHIA COLI*

Abstract— Growth delay was induced with near-UV (334 nm) radiation in Escherichia coli K12 bacterial strains followed by attempts at photoreactivation (PR) of this effect at 405 nm. In the UV-sensitive strain AB2480, a small PR of the observed population growth delay occurred after 334 nm irradiation at 35°C and a much larger PR after 334 nm irradiation at 5°C. However, much of the population growth delay in this strain can be explained as being due to killing, and all or most of the observed PR pertains only to this killed fraction of the population. The true cell growth delay (i.e. that of surviving cells) thus appears to be only slightly, if at all, photoreactivable. This conclusion is supported by studies with a wild-type strain KW8, which shows growth delay at non-lethal doses; this growth delay shows no PR, regardless of the temperature during 334 nm irradiation. These findings indicate that photoreactivable lesions (cyclo-butyl pyrimidine dimers) are not an important cause of near-UV-induced growth delay. Strain AB2480 lacks known dark-repair systems for DNA damage induced by far-UV (below 300 nm) radiation, yet shows the same efficiency for 334-nm-induced growth delay as the wild type, which possesses these dark repair systems. This indicates that lesions in DNA that are dark-repairable by the systems not tunctional in AB2480are not responsible for 334-nm-induced growth delay. It is possible, however, that fragmentary repair systems in AB2480 can operate on some DNA lesion that might cause growth delay. Spontaneously decaying lesions are unlikely, since growth-delay damage decays at a very low rate in non-nutrient medium. Since most of the known types of DNA damage and repair are thus eliminated, these considerations suggest that DNA damage is not involved in near-UV-induced growth delay.     

Effects of glucose,glutamine, and malate on the metabolism of spodoptera frugiperda clone 9 (sf9) cells

Optimal design and operation of bioreactors for insect cell culture is facilitated by functional relations providing quantitative information on cellular metabolite consumption kinetics, as well as on the specific cell growth rates (μ_G). Initial specific consumption rates of glucose, malate, and oxygen, and associated changes in μ_G, were measured forSpodoptera frugiperda clone 9 (Sf9) cells grown in batch suspension culture in medium containing 7–35 mM glucose, 0–16 mM malate, and 4–16 mM glutamine. The initial specific glucose consumption rate (q _G ) could be described by a modified Michaelis-Menten equation treating malate as a “competitive” inhibitorK ₁ = 6.5 mM) and glutamine as a “noncompetitive” inhibitorK _I = 14 mM) ofq _G , with aK _m of 7.1 mM for glucose. All three carbon sources were found to increase μ_G in a saturable manner, and a modified Monod equation was employed to describe this relationship (μ_Gmax = 0.047 h^-1). The initial specific oxygen consumption rate (q_O2) in Sf9 cells could be related to μ_G by the maintenance energy model, and it was calculated that, under typical culture conditions, about 15–20% of the cellular energy demand comes from functions not related to growth. Fitted parameters in mathematical expression for μg: K₄, Monod constant for glucose (mM); K₅, modified Monod constant for malate (mM); K₆, Monod constant for glutamine (mM); m_o2, specific consumption rate of oxygen by the cells under zero-growth conditions (nmol/cell/h); q_F, initial specific fumarate production rate (nmol/cell/ h);q _G , initial specific glucose consumption rate (nmol/cell/h); q_Gmax, maximum initial specific glucose consumption rate (nmol/cell/h);q _M , initial specific malate consumption rate (nmol/cell/h); q_o2, initial specific oxygen consumption rate (nmol/cell/h); Y_o2, cell yield on oxygen (cells/nmol); μ, initial specific cell growth rate (h^-1); μ_g, initial specific cell growth rate (h^-1); μG_max, maximum initial specific cell growth rate (h^-1).     

An n-Type Conjugated Oligoelectrolyte Mimics Transmembrane Electron Transport Proteins for Enhanced Microbial Electrosynthesis

Interfacing bacteria as biocatalysts with an electrode provides the basis for emerging bioelectrochemical systems that enable sustainable energy interconversion between electrical and chemical energy. Electron transfer rates at the abiotic-biotic interface are, however, often limited by poor electrical contacts and the intrinsically insulating cell membranes. Herein, we report the first example of an n-type redox-active conjugated oligoelectrolyte, namely COE-NDI , which spontaneously intercalates into cell membranes and mimics the function of endogenous transmembrane electron transport proteins. The incorporation of COE-NDI into Shewanella oneidensis MR-1 cells amplifies current uptake from the electrode by 4-fold, resulting in the enhanced bio-electroreduction of fumarate to succinate. Moreover, COE-NDI can serve as a “protein prosthetic” to rescue current uptake in non-electrogenic knockout mutants.     

The Short-Term Exposure to SDHI Fungicides Boscalid and Bixafen Induces a Mitochondrial Dysfunction in Selective Human Cell Lines

Fungicides are used to suppress the growth of fungi for crop protection. The most widely used fungicides are succinate dehydrogenase inhibitors (SDHIs) that act by blocking succinate dehydrogenase, the complex II of the mitochondrial electron transport chain. As recent reports suggested that SDHI-fungicides could not be selective for their fungi targets, we tested the mitochondrial function of human cells (Peripheral Blood Mononuclear Cells or PBMCs, HepG2 liver cells, and BJ-fibroblasts) after exposure for a short time to Boscalid and Bixafen, the two most used SDHIs. Electron Paramagnetic Resonance (EPR) spectroscopy was used to assess the oxygen consumption rate (OCR) and the level of mitochondrial superoxide radical. The OCR was significantly decreased in the three cell lines after exposure to both SDHIs. The level of mitochondrial superoxide increased in HepG2 after Boscalid and Bixafen exposure. In BJ-fibroblasts, mitochondrial superoxide was increased after Bixafen exposure, but not after Boscalid. No significant increase in mitochondrial superoxide was observed in PBMCs. Flow cytometry revealed an increase in the number of early apoptotic cells in HepG2 exposed to both SDHIs, but not in PBMCs and BJ-fibroblasts, results consistent with the high level of mitochondrial superoxide found in HepG2 cells after exposure. In conclusion, short-term exposure to Boscalid and Bixafen induces a mitochondrial dysfunction in human cells.     

The roles of the rel+ gene and of 4-thiouridine in killing and photoprotection of Escherichia coli by near-ultraviolet radiation

Abstract— Photoprotection is a reduction in response to far-UV (190–300. nm) radiation in cells that have been previously exposed to longer wavelengths. It has been proposed that photoprotection operates by means of a growth delay that permits more time for dark repair. Growth delay in Escherichia coli utilizes 4-thiouridine (⁴Srd) in transfer RNA as a chromophore and it requires the rel⁺ gene, which exerts a stringent control upon RNA synthesis. Mutants that were either rel or ⁴Srd^? were isolated from E. coli B, utilizing a near-UV-induced growth-delay selection technique. The rel mutants, which undergo little growth delay after near-UV irradiation, show only 50% as much photoprotection as wild types, while ⁴Srd^? mutants show no photoprotection at all. Thus, photoprotection appears to utilize ⁴Srd as its sole chromophore in E. coli B and B/r, and no more than 50% of photoprotection in these strains can be a result of near-UV-induced growth delay.