An Extracellular Protein of Propionic Acid Bacteria Inhibits Induced Mutations in Salmonella typhimurium Strains

A culture of propionic acid bacteria grown in a glucose-containing minimal medium, as well as the culture liquid and logarithmic-phase cells obtained from this culture, were found to inhibit the base pair substitution mutations induced by 4-nitroquinoline N-oxide, N-methyl-N"-nitro-N-nitrosoguanidine, and sodium azide and the frameshift mutations induced by 9-aminoacridine. The antimutagenic activity of the culture liquid (CL) was presumably due to the presence of an extracellular thermolabile protein with a molecular mass of no more than 12 kDa, as evidenced by the facts that this activity considerably decreased after the treatment of the CL with pronase, its heating at 92°C, and its dialysis in a cellulose sack, which retains substances with molecular masses greater than 12 kDa. The residual antimutagenic activity of the dialyzed culture liquid was probably related to the interaction of the mutagen with thiols, rather than to the presence of organic acids (acetic or propionic). Thiols may also contribute to the antimutagenic activity of the Propionibacterium shermanii cells.     

Extracellular protein of propionic acid bacteria inhibits induced mutation in strains of Salmonella typhimurium

A culture of propionic acid bacteria grown in a glucose-containing minimal medium, as well as the culture liquid and logarithmic-phase cells obtained from this culture, were found to inhibit the base pair substitution mutations induced by 4-nitroquinoline N-oxide, N-methyl-N'-nitro-N-nitrosoguanidine, and sodium azide and the frameshift mutations induced by 9-aminoacridine. The antimutagenic activity of the culture liquid (CL) was presumably due to the presence of an extracellular thermolabile protein with a molecular mass of no more than 12 kDa based on the facts that this activity considerably decreased after the treatment of the CL with pronase, its heating at 92 degrees C, and its dialysis in a cellulose sack, which retains substances with molecular masses greater than 12 kDa. The residual antimutagenic activity of the dialyzed culture liquid was probably related to the interaction of the mutagen with thiols, rather than to the presence of organic acids (acetic or propionic). Thiols may also contribute to the antimutagenic activity of the P. shermanii cells.     

A positive effect of Propionibacterium freudenreichii on the growth of Saccharomyces cerevisiae during their cocultivation

The growth pattern of Saccharomyces cerevisiae and Propionibacterium freudenreichii ssp. shermanii (P. shermanii; propionic acid bacteria, PABs) during cocultivation in liquid media depended on the ratio of the cells in the inoculum. An increase in the growth rate of S. cerevisiae was observed at a PAB to yeast ratio of approximately 3: 1; higher ratios exerted adverse effects on yeast growth. The culture liquid of 18-to 24-h (young) cultures of PABs stimulated yeast growth. Although yeast growth-stimulating exometabolites of PABs were not high-molecular-weight compounds, they were thermolabile. When present in the medium at concentrations of up to 1.5%, the antimicrobial agent sodium propionate did not interfere with S. cerevisiae growth; however, it completely inhibited the growth of B. subtilis at a concentration of 0.2%.     

The antimutagenic effect of a truncated ε subunit of DNA polymerase III inEscherichia coli cells irradiated with UV light

It has previously been suggested that inhibition of the proofreading 3′-5′ exonuclease activity of DNA polymerase may play an important role in generation of UV-induced mutations inEscherichia coli. Our previous work showing that overproduction of ε, the proofreading subunit of DNA polymerase III, counteracts the SOS mutagenic response ofE. coli seemed to be consistent with this hypothesis. To explore further the nature of the antimutagenic effect of ε we constructed plasmid pMK17, which encodes only two of the three highly conserved segments of ε — Exol and ExoII; the third segment, ExoIII, which is essential for 3′–5′ exonuclease activity, is deleted. We show that at 40°C, over-production of the truncated e subunit significantly delays production of M13 phage, suggesting that the protein retains its capacity to bind to DNA. On the other hand, the presence of pMK17 in atrpE65 strain growing at 40°C causes a 10-fold decrease in the frequency of UV-induced Trp⁺ mutations. This antimutagenic effect of the truncated s is effectively relieved by excess UmuD,C proteins. We also show that the presence of plasmid pIP21, which contains thednaQ49 allele encoding an ε subunit that is defective in proofreading activity, almost completely prevents generation of UV-induced mutations in thetrpE65 strain. We propose that the DNA binding ability of free ε, rather than its 3′–5′ exonuclease activity, affects processing of premutagenic UV-induced lesions, possibly by interfering with the interaction between the UmuC-UmuD′-RecA complex and Pol III holoenzyme. This interaction is probably a necessary condition for translesion synthesis.     

The relationship between frameshift mutagenicity and DNA-binding affinity in a series of acridine-substituted derivatives of the experimental antitumour drug 4′-(9-acridinylamino)methanesulphonanilide (AMSA)

The mutagenicity and DNA-binding affinity of members of a series of acridine-substituted derivatives of 4′-(9-acridinylamino)methanesulphonanilide (AMSA) have been compared. The series includes compounds ranging from highly active to inactive in the L1210 murine leukaemia. Binding to DNA was measured by an ethidium displacement technique, with a correction being made for acridine-induced quenching of ethidium. Mutagenicity was assessed by measuring the reversion frequencies of the frameshift tester strain Salmonella typhimurium TA1537 in liquid culture. The results indicate that maximum mutagenicity is found in a “window” of DNA-binding affinities between 10⁶ and 5 × 10⁶ M^?1 (determined at 0.01 ionic strength). Compounds with binding affinities below 10⁶ M^?1 generally lacked both antitumour and mutagenic activity, whereas those with affinities above 5 × 10⁶ M^?1 were active against L1210 leukaemia but virtually inactive in inducing frameshift mutations.     

The possible role of probiotics as dietary antimutagens

Possible antimutagenic actions of probiotics - mainly lactic acid bacteria - were examined using in vitro and in vivo test systems.In the Ames test with Salmonella typhimurium TA1538 beef extract and nitrosated beef extract were used as mutagens. L. casei showed high antimutagenic activity on mutagenicity induced by nitrosated beef extract only without S9 mix, whereas Omniflora (a lyophilized preparation of lactobacilli and E. coli and its cellfree culture broth exhibited antimutagenic action only on beef extract.The actions of probiotics were more homogeneous when living animais were used in the tests. Using busulfan as a mutagen both the chromosome aberration test (with Chinese hamster bone marrow cells) and the micronucleus test (with bone marrow cells of Chinese hamsters and mice) showed strong anticlastogenic action when L. casei, Omniflora or yoghurt (with living bifiobacteria) were given orally at the same time as the mutagen. Lactobacilli were effective also after i.p. injection. Cell-free culture broths had no or only weak antimutagenic effects. Mutagen-induced chromosome aberrations and micronuclei were reduced by up to 80% by the lactobacilli.     

The reversion of trp frameshift mutations in mut,polA, lig and dnaE mutant strains of Escherichia coli

Mutator mutations mutL25, mutR34, and mutU4 had similar effects on the reversion of 4 trp frameshift mutations of known sequence. The mutation trpE9777, which resulted from the addition of an A–T base-pair to a run of 5 A–T base-pairs, was most strongly reverted by the 4 mutators. Reversion of trpE9777 was also increased by mutation polA1 (DNA polymerase I) and dnaE486 and dnaE511 (DNA polymerase III). No effect was found with the ligase mutations, lig-4 or lig-ts7. Mutations polAex1 and polA107, both deficient in the 5′ → 3′ exonuclease activity of DNA polymerase I, had different mutator effects; the factor increase in reversion of trpE9777 was 28-fold for polAex1, 6-fold for polA107, and 21-fold for polA1. The trpE9777 mutation is a useful indicator of frameshift mutator activity.     

The geptrong pharmaceutical product increases efficiency of postreplication repair of permutation intermediates in yeast Saccharomyces cerevisiae

Geptrong is a medication from pure defermentated honey. In medical practice, it is used as hepatoprotector. Genotoxicity analysis revealed antimutagenic activity of the preparation. The spontaneous mutation rate at the ADE4-ADE8 and CAN1 loci was several times lower in case that the yeast cells were plated on the geptrong-containing medium, and the mutation rate was scored using the method of ordered plating. If spontaneous mutation rate was measured by means of the fluctuation method of median, no antimutagenic activity was detected. Geptrong had no effect on the yeast cell survival. At the same time, it substantially decreased the frequency of direct mutations at the ADE4-ADE8 locus, induced by UV-and gamma-radiation, and ethylmetansulfonate. The effect of the geptrong antimutagenic activity on the level of UV-induced mutagenesis in the yeast strains defective for the repair systems rad2, rad51, rad54, rad59, msh2, and hsm3 was examined. Antimutagenic activity was detected in the wild type, as well as in the rad2, rad54, rad59, and hsm3 strains, while rad51, pms1, and msh2 mutants lacked this activity. Based on these data, it is suggested that antimutagenic effect of geptrong is associated with activated repair of mismatches, appeared during the postreplicative recombination repair.     

Antimutagenicity of hops (Humulus lupulus L.): bioassay-directed fractionation and isolation of xanthohumol

Bioassay-directed fractionation with a Salmonella/microsomal assay against the food borne mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was used to identify antimutagenic components of hops. Hops pellets extracted with diethylether showed antimutagenic activity against mutations induced by IQ. Fractionation of the diethylether extract (DE) by column chromatography, followed by semi-preparative HPLC yielded two fractions (E4b and E4d) with strong antimutagenic activity against IQ induced mutations. Separation of fraction E4b resulted in inactive fractions, while fraction E4d has been identified to be xanthohumol. In mammalian test system with human hepatoma HepG2 cells fraction E4d at 10 μg/ml completely prevented formation of IQ induced DNA damage. These results indicate that xanthohumol is a very promising potential protective agent against genotoxicity of food borne carcinogens, which warrants further investigation.     

Antimutagenesis of multiphytoadaptogene in yeast Saccharomyces

Multiphytoadaptogene (MPA) consists of plant extracts components including adaptogenes. Genotoxicity analysis revealed the antimutagenic activity of MPA. MPA decreased the direct mutations frequency in ADE4-ADE8 loci induced by UV radiation and nitrous acid by 3.7 and 33 times, respectively. The lethal effect of UV radiation was inhibited when the preparation preparation MFA was used on complete medium with ethanol. MPA had no effect on replicative mutagenesis. At the same time it depressed mutagenesis caused by repair errors. The data obtained suggest the antimutagenic activity of multiphytoadaptogene is associated with postreplicative repair activation.     

Commensalistic Interaction Between Lactobacillus acidophilus and Propionibacterium shermanii

Propionibacterium shermanii and Lactobacillus acidophilus were grown in batch mixed culture in a 5-liter fermenter under controlled conditions of pH 5.8 and 35°C on a semisynthetic medium with glucose as an energy source. Cellular efficiencies and fermentation balances were developed for this pair and compared with P. shermanii grown in pure culture on glucose, lactate, and a mixture of these substrates and with L. acidophilus grown on glucose. P. shermanii had ATP yield coefficient values of 17 for each substrate alone but had an average value of 30 for substrate mixtures. Growth rates were similar for P. shermanii on glucose or lactate but higher cell yields were observed for glucose. P. shermanii used both lactate and glucose in mixed substrate until lactate was exhausted, and growth rates slowed thereafter. L. acidophilus had a similar ATP yield coefficient of 15 but produced lower cell yields than did P. shermanii on glucose. Mixed culture of both microorganisms on glucose resulted in much faster and nearly equal growth rates for both and no lactate accumulation in the medium. Acetic acid production rates per generation were lower in mixed culture, suggesting use by the growing culture. The cause of the synergistic effect was not determined but may be due to the rapid production and removal of lactate or CO₂ enhancement in mixed culture.     

Detection and partial characterization of lymphoid cell surface proteases

Cultures of viable thymocytes and lymph node cells (LNC) were found to exhibit neutral protease activity toward radiolabeled protein substrates. Proteases were not actively secreted in serum-free culture. Thymocyte surface proteases were not affected by incubation of the cells in 1 mM ethylenediaminetetraacetic acid (EDTA) or 1 mM ethylene glycol bis(aminoethyl ether) N, N'-tetraacetic acid (EGTA); however, approximately 25% of lymph node cell surface protease activity was released from the cells by EDTA. It was concluded that the majority of protease activity displayed by both cell types was tightly associated with the cell surface. The inhibitor sensitivity of the cell surface proteases detected on hamster thymocytes and LNC and rat thymocytes was very similar. Cell surface protease activity was inhibited (85%) by the serine protease inhibitors diisopropylfluorophosphate (DFP) and phenylmethylsulfonylfluoride (PMSF) and was partially inhibited by l-1-tosylamide-2-phenylethylchloromethyl ketone(TPCK) and soybean trypsin inhibitor (SBTI), but not by N-α-p-tosyl-l-lysine-chloromethyl ketone (TLCK) or ?-aminocaproic acid (EACA). The bacterial protease inhibitor antipain was strongly inhibitory whereas leupeptin was less effective and elastinal did not inhibit cell surface protease activity. Thymocyte surface proteases were also inhibited (65%) by ZnCl₂, but not be several other divalent cations. In LNC, both ZnCl₂ and NiCl₂ were inhibitory to a lesser extent (32% inhibition). At least one surface protease in both thymocytes and LNC could function as a plasminogen activator.     

Eliminating Anti-Nutritional Plant Food Proteins: The Case of Seed Protease Inhibitors in Pea

Several classes of seed proteins limit the utilisation of plant proteins in human and farm animal diets, while plant foods have much to offer to the sustainable intensification of food/feed production and to human health. Reduction or removal of these proteins could greatly enhance seed protein quality and various strategies have been used to try to achieve this with limited success. We investigated whether seed protease inhibitor mutations could be exploited to enhance seed quality, availing of induced mutant and natural Pisum germplasm collections to identify mutants, whilst acquiring an understanding of the impact of mutations on activity. A mutant (TILLING) resource developed in Pisum sativum L. (pea) and a large germplasm collection representing Pisum diversity were investigated as sources of mutations that reduce or abolish the activity of the major protease inhibitor (Bowman-Birk) class of seed protein. Of three missense mutations, predicted to affect activity of the mature trypsin / chymotrypsin inhibitor TI1 protein, a C77Y substitution in the mature mutant inhibitor abolished inhibitor activity, consistent with an absolute requirement for the disulphide bond C77-C92 for function in the native inhibitor. Two further classes of mutation (S85F, E109K) resulted in less dramatic changes to isoform or overall inhibitory activity. The alternative strategy to reduce anti-nutrients, by targeted screening of Pisum germplasm, successfully identified a single accession (Pisum elatius) as a double null mutant for the two closely linked genes encoding the TI1 and TI2 seed protease inhibitors. The P. elatius mutant has extremely low seed protease inhibitory activity and introgression of the mutation into cultivated germplasm has been achieved. The study provides new insights into structure-function relationships for protease inhibitors which impact on pea seed quality. The induced and natural germplasm variants identified provide immediate potential for either halving or abolishing the corresponding inhibitory activity, along with associated molecular markers for breeding programmes. The potential for making large changes to plant protein profiles for improved and sustainable food production through diversity is illustrated. The strategy employed here to reduce anti-nutritional proteins in seeds may be extended to allergens and other seed proteins with negative nutritional effects. Additionally, the novel variants described for pea will assist future studies of the biological role and health-related properties of so-called anti-nutrients.     

Isolation and determination of the activity of IgA1 protease from Neisseria meningitidis

A method of the isolation and purification of IgA1 protease from a culture of Neisseria meningitidis serogroup A has been developed. Three inactivated intermediates of the production of the meningococcal vaccine, a culture liquid, as well as a supernatant and precipitate obtained by the precipitation of bacterial cells by cetavlon, served as a starting material. The purity of IgA1 protease was determined by SDS-PAGE. An immunoenzyme assay for determining the IgA1 protease activity has been developed. The yield of the enzyme with a specific activity of 0.5 to 4 million units/mg from 103 g of the cetavlon precipitate (40 l of culture liquid) was about 600 µg. It was shown that IgA1 protease isolated from serogroup A meningococcus is capable of protecting experimental animals (mice) infected with meningococcus of serogroup B.     

Involvement of umuDC ST genes in nitropyrene-induced -CG frameshift mutagenesis at the repetitive CG sequence in the hisD3052 allele of Salmonella typhimurium

Expression of the umuDC operon is required for UV and most chemical mutagenesis in Escherichia coli. The closely related species Salmonella typhimurium has two sets of umuDC-like operons, umuDC _ST on the chromosome and samAB on a 60-MDa cryptic plasmid. The roles of theumuDC-like operons in chemically induced frameshift mutagenesis of the hisD3052 allele of S. typhimurium were investigated. Introduction of a pBR322-derived plasmid carrying umuDCST increased the rate of reversion of hisD3052, following treatment with 1-nitropyrene (1-NP) or 1,8-dinitropyrene (1,-8DNP) tenfold and fivefold, respectively, whereas it did not substantially increase the rate of reversion induced by other frameshift mutagens, i.e. 2-nitrofluorene (2NF) and 2-amino- 3-methyldipyrido[1,2-a:3 ′,2′-d]imi-dazole (Glu-P-1). Introduction of a pBR322-derived plasmid carrying samAB did not increase the incidence of reversion of hisD3052 observed with any of the mutagens examined. Deletion of umuDC _STSubstantially lowered the reversion rate induced by l-NP or 1,8-DNP, but it did not affect reversion induced by 2-NF, Glu-P-1 or N-hydroxyacetylaminofluorene (N-OH-AAF). Deletion of samAB had little impact on reversion incidence induced by any of the five frameshift mutagens. DNA amplification using the polymerase chain reaction technique followed by restriction enzyme analysis using BssHII, suggested that the mutations induced by the five frameshift mutagens were all CG deletions at the CGCGCGCG sequence in hisD3052. These results suggest that umuDCST, but not samAB, is involved in the -2 frameshift mutagenesis induced by l-NP and 1,8-DNP at the repetitive CG sequence, whereas neither operon participates in induction of the same type of mutations by 2-NF, Glu-P-1 or N-OH-AAF.     

Mutational specificities of 1′-acetoxysafrole,N-benzoyloxy-N-methyl-4-aminoazobenzene,and ethyl methanesulfonate in human cells

We have used an oriP-tk shuttle vector t determine the types of mutations induced in human cells by ethyl methanesulfonate (EMS), 1'-acetoxysafrole (AcOS), and N-benzoyloxy-N-methyl-4-aminoazobenzene (BzOMAB). Plasmid DNA was treated in vitro with mutagen and electroporated into human lymphoblastoid cells. After replication of the vector in human cells, plasmids were analyzed for mutations in the herpes simplex virus type 1 thymidine kinase gene. Ethyl methanesulfonate induced predominantly GC → AT transition mutations. Treatment of the shuttle vector with AcOS induced 5 of the 6 possible base substitution mutations, including GC → AT (32%) and AT → GC (14%) transition mutations, GC → TA (%), GC → CG (18%), and AT → TA (14%) transversion mutations, as well as a low frequency (9%) of −1 frameshift mutations at GC base pairs. Replication in human cells of DNA modified with BzOMAB yielded a significant increase (17-fold) in the frequency of deletion mutations relative to solvent-treated DNA. A majority (94%) of the point mutations induced by BzOMAB occurred at GC base pairs and were predomianntly GC → AT transitions (33%) and −1 frameshift (22%) mutations, with the remainder consisting mainly of transversions at GC base pairs (28%). The broad spectrum of base substitution mutations observed for AcOS and BzOMAB may indicate the frequent insertion of a variety of bases during replicative bypass of aralkylated bases in human cells.     

Design and biological evaluation of novel HIV-1 protease inhibitors with isopropanol as P1′ ligand to enhance binding with S1′ subsite

Newly designed HIV-1 protease inhibitors that maximize interactions with the protein backbone, especially in the form of hydrogen bonds, may enhance the antiviral potency of these compounds and minimize acquisition of drug-resistant mutations. Herein, we described a series of new HIV-1 PIs containing phenols as the P2 ligands and chiral isopropanol as the P1′ ligands, in combination with 4-trifluoromethylphenylsulfonamide or 4-nitrophenylsulfonamide as the P2′ ligands. And most of these compounds exhibited nanomolar inhibitory potency. In particular, inhibitors 13c and 13e with 4-trifluoromethylphenylsulfonamide as the P2′ ligand and (R) – isopropanol as the P1′ ligand, exhibited antiviral IC₅₀ values of 1.64 nM and 2.33 nM, respectively. Furthermore, they also showed remarkable activity against wild-type and DRV-resistant HIV-1 variants that raised the prospect of designing more effective PIs further.     

Antimutagen from leaves of Carmona retusa (Vahl) Masam.

An antimutagenic principle was extracted from the leaves of Carmona retusa with ethyl alcohol. This was then purified by solvent partition and liquid chromatography. The micronucleus test, an in vivo method, using albino mice as the test system was used for monitoring the antimutagenic activity. At a dosage of 23.4 mg/kg body weight, the pure isolate reduced by 68.4% the number of micronucleated polychromatic erythrocytes induced by the mutagen tetracycline. Statistical analysis (one-way ANOVA) shows that the variance of the pure isolate differs significantly from that of tetracycline, a known mutagen.     

The effect of extracellular metabolites on the frequency of thy+ revertants in Salmonella typhimurium populations

There is convincing evidence that adaptation and survival processes in bacterial populations depend on cell-to-cell interactions. Our studies showed that the frequency of stress-induced His⁺ reversions in an amino-acid-starved Salmonella typhimurium culture is inversely proportional to cell density in this culture. The effects of cell density and of different culture liquids prepared from cultures starved for histidine on the frequency of Thy⁺ revertants were also studied. It was found that the frequency of Thy⁺ revertants is inversely proportional (r = ?0.74) to the density of the bacterial culture starved of thymine. The culture liquid prepared from the culture starved of histidine exerted an inhibitory effect on the frequency of Thy⁺ reversions, indicating that mutations induced by different types of stress have a common mechanism. The study of the effect of the culture liquid prepared from a histidine-starved culture on the frequency of ethyl-methanesulfonate-induced His⁺ revertants showed that this liquid prevented the induction of His⁺ reversions.     

Partial purification and properties of Galleria mellonella larvae proteolytic inhibitors acting on Metarhizium anisopliae toxic protease

Gel permeation, preparative isoelectric focusing, and affinity chromatography were used to purify three inhibitors of proteolytic activity from perchloric acid extracts of last instar Galleria mellonella larvae. Electrofocusing experiments revealed three isoinhibitors with different isoelectric points: inhibitor I-1 with p1 of pH 5.6, inhibitor I-2, pH 7.7, and inhibitor I-3 (of small inhibitory activity), pH 8.6. By affinity chromatography on trypsin-Sepharose 4B the I-1 was purified 9.7 ×, but 71.1% of inhibitory activity was lost. Molecular mass of the inhibitory complex was 12,600 Da. I-1 and I-2 are relatively stable to heat at several pHs with minor stability at pH 10. I-1 and I-2 inhibit serine proteases about 2.5 times as much as sulfhydryl proteases. In the same ratio protease P-1 and protease P-2 from Metarhizium anisopliae are inhibited.