SOS Chromotest methodology for fundamental genetic research

Chromogenic Escherichia coli reporter strain for screening DNA damaging agents

The presence of pollutants in soil and water has given rise to diverse analytical and biological approaches to detect and measure contaminants in the environment. Using bacterial cells as reporter strains represents an advantage for detecting pollutants present in soil or water samples. Here, an Escherichia coli reporter strain expressing a chromoprotein capable of interacting with soil or water samples and responding to DNA damaging compounds is validated. The reporter strain generates a qualitative signal and is based on the expression of the coral chromoprotein AmilCP under the control of the recA promoter. This strain can be used simply by applying soil or water samples directly and rendering activation upon DNA damage. This reporter strain responds to agents that damage DNA (with an apparent detection limit of 1 µg of mitomycin C) without observable response to membrane integrity damage, protein folding or oxidative stress generating agents, in the latter case, DNA damage was observed. The developed reporter strain reported here is effective for the detection of DNA damaging agents present in soils samples. In a proof-of-concept analysis using soil containing chromium, showing activation at 15.56 mg/L of Cr(VI) present in soil and leached samples and is consistent with Cr(III) toxicity at high concentrations (130 µg). Our findings suggest that chromogenic reporter strains can be applied for simple screening, thus reducing the number of samples requiring analytical techniques.

Conidiation under illumination enhances conidial tolerance of insect-pathogenic fungi to environmental stresses

Light is an important signal for fungi in the environment and induces many genes with roles in stress and virulence responses. Conidia of the entomopathogenic fungi Aschersonia aleyrodis, Beauveria bassiana, Cordyceps fumosorosea, Lecanicillium aphanocladii, Metarhizium anisopliae, Metarhizium brunneum, Metarhizium robertsii, Simplicillium lanosoniveum, Tolypocladium cylindrosporum, and Tolypocladium inflatum were produced on potato dextrose agar (PDA) medium under continuous white light, on PDA medium in the dark, or under nutritional stress (= Czapek medium without sucrose = MM) in the dark. The conidial tolerance of these species produced under these different conditions were evaluated in relation to heat stress, oxidative stress (menadione), osmotic stress (KCl), UV radiation, and genotoxic stress caused by 4-nitroquinoline 1-oxide (4-NQO). Several fungal species demonstrated greater stress tolerance when conidia were produced under white light than in the dark; for instance white light induced higher tolerance of A. aleyrodis to KCl and 4-NQO; B. bassiana to KCl and 4-NQO; C. fumosorosea to UV radiation; M. anisopliae to heat and menadione; M. brunneum to menadione, KCl, UV radiation, and 4-NQO; M. robertsii to heat, menadione, KCl, and UV radiation; and T. cylindrosporum to menadione and KCl. However, conidia of L. aphanocladii, S. lanosoniveum, and T. inflatum produced under white light exhibited similar tolerance as conidia produced in the dark. When conidia were produced on MM, a much stronger stress tolerance was found for B. bassiana to menadione, KCl, UV radiation, and 4-NQO; C. fumosorosea to KCl and 4-NQO; Metarhizium species to heat, menadione, KCl, and UV radiation; T. cylindrosporum to menadione and UV radiation; and T. inflatum to heat and UV radiation. Again, conidia of L. aphanocladii and S. lanosoniveum produced on MM had similar tolerance to conidia produced on PDA medium in the dark. Therefore, white light is an important factor that induces higher stress tolerance in some insect-pathogenic fungi, but growth in nutritional stress always provides in conidia with stronger stress tolerance than conidia produced under white light.

In vitro protective effects of two extracts from bergamot peels on human endothelial cells exposed to tumor necrosis factor-alpha (TNF-alpha)

Bergamot ( Citrus bergamia Risso) is a less commercialized Citrus fruit, mainly used for its essential oil extracted from the peel. Bergamot peel (BP) represents about 60% of the processed fruits and is regarded as primary waste. However, it contains good amounts of useful compounds, such as pectins and flavonoids. Many of the bioactivities of Citrus flavonoids appear to impact vascular endothelial cells. Herein, we report the protective effect of two flavonoid-rich extracts from BP (endowed with radical-scavenging properties and lacking genotoxic activity) against alterations in cell modifications induced by the pleiotropic inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) on human umbilical vein endothelial cells (HUVECs), as demonstrated by monitoring intracellular levels of malondialdehyde/4-hydroxynonenal, reduced and oxidized glutathione and superoxide dismutase activity, and the activation status of nuclear factor-kappaB (NF-kappaB). Thus, BP appears to be a potential source of natural antioxidant/anti-inflammatory phytocomplexes to be employed as ingredients of nutraceutical products or functional foods.

Evidence for in vitro anti-genotoxicity of cheese non-starter lactobacilli

The inhibition of direct acting DNA reactive agents by 63 non-starter lactobacilli isolated from raw ewes milk cheeses was examined by short-term assay (SOS-Chromotest) and compared with already characterized starter lactobacilli. The screening revealed strains active against the nitroarene 4-nitroquinoline-1-oxide (NQO) and the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in different species of the genus Lactobacillus (L. rhamnosus, L. casei, L. plantarum, L. brevis, Lactobacillus spp.). It was proved that the anti-genotoxicity was strain-dependent, and always associated with spectroscopic modification of genotoxins. The frequency of strains inhibiting nitroarene genotoxicity was comparable for non-starter and starter lactobacilli, whereas inhibition of the alkylating agent was largely predominant in non-starter isolates. Seventeen strains presented inhibitory activity against both genotoxins. DNA RAPD-PCR performed with M13, Pro-Up and RPO2 primers on the lactobacilli under examination showed genetic diversity in these strains. The non-starter isolates clustered in seven groups and the strains presenting a high degree of activity against 4-nitroquinoline-1-oxide clustered in a single group with a similarity around 75%. Interestingly, the strains with anti-genotoxic properties also showed acid-bile tolerance, indicating that the autochthonous lactobacilli which survive cheese ripening may also reach the gut as viable cells and could prevent genotoxin DNA damage to enterocytes, as is desirable for probiotic bacteria.

Screening of potential lactobacilli antigenotoxicity by microbial and mammalian cell-based tests

Antigenotoxicity is considered an important property for probiotic lactobacilli. The ability of non probiotic lactobacilli from dairy products and starters to inhibit two reference genotoxins: 4-nitroquinoline-1-oxide and N-methyl-N'-nitro-N-nitrosoguanidine was evaluated. The study was carried out using short-term assays with different targets, such as procaryotic cells (SOS-Chromotest for genotoxicity in Escherichia coli and Ames test for mutagenicity in Salmonella typhimurium) and eucaryotic cells (Comet assay for genotoxicity in Caco-2 enterocytes). A high proportion of strains inhibiting 4-nitroquinoline-1-oxide activity was found in Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus plantarum. Inhibition of N-methyl-N'-nitro-N-nitrosoguanidine activity occurred in only one L. acidophilus strain. All the strains with antigenotoxic properties also demonstrated antimutagenic activity and produced modifications in genotoxin spectroscopic profiles. Strain viability during and after genotoxin exposure was confirmed. Concordance of the results obtained with microbial and mammalian cell-based tests is underlined.