Comparative lectin-binding and agglutination properties of the strain-specific,TA3-St,and the non-strain-specific,TA3-Ha,murine mammary carcinoma ascites sublines. Further studies of receptors in epiglycanin

The complex carbohydrates at the cell surfaces of two TA3, murine mammary carcinoma ascites sublines (the strain-specific, TA3-St subline and the nonstrain-specific, TA3-Ha line) were compared by binding studies with ¹²⁵I-labelled concanavalin A (con A), Ricinis communis agglutinin (RCA), and eel-serum agglutinin (ESA). The TA3-Ha cell bound equal amounts of con A, 1.5-fold more RCA, and 4-fold more ESA than the TA3-St cell. Binding-inhibition studies by these lectins and two others [wheat-germ agglutinin (WGA) and potato lectin (STA)] suggest complementary binding-sites between con A and both RCA and ESA. Quantitative agglutination studies with the five lectins, and inhibition determinations by both neuraminidase-treated and untreated epiglycanin revealed that TA3-St, but not TA3-Ha, cells were agglutinated by con A, and that epiglycanin inhibited this agglutination, as well as the agglutination of rabbit erythrocytes by con A. The presence of a con A receptor on epiglycanin was also suggested by the binding of epiglycanin to con A-Sepharose, and its specific elution with methyl α-d-manno-pyranoside. TA3-St cells were agglutinated at a 10-15-fold lower concentration of either STA or RCA than TA3-Ha cells, but both cells were agglutinated by the same concentration of WGA and ESA. Inhibition by epiglycanin of agglutination of TA3-St cells by either STA or ESA occurred at a concentration lower than that of TA3-Ha cells, but epiglycanin inhibited RCA agglutination of TA3-Ha cells at a concentration     

Synthesis and mutagenicity of 2-aryl-substitute ( o -hydroxy-, m -bromo-, o -methoxy-, o -nitro-phenyl or 4-pyridyl) benzothiazole derivatives on Salmonella typhimurium and human lymphocytes exposed in vitro

Derivatives of 2-aryl-substitute (o-hydroxy-, m-bromo-, o-methoxy-, o-nitro-phenyl or 4-pyridyl) benzothiazole were synthesized and tested for their mutagenicity in in vitro assays: (i) in the Ames test with Salmonella typhimurium TA98 and TA100 strains; and (ii) in the sister chromatid exchange (SCE) in cultured human lymphocytes. The four of compounds (BT-11, B-12, BT-14 and BT-15) caused statistically significant increase in revertant colonies of TA98 and TA100. Treatment of lymphocytes with compounds also caused a significant increase in SCE/cell in association with high levels and long exposure (300 μg/mL and 48 h) of the four compounds. It can be concluded that benzothiazole derivatives showed mutagenic activity and were also able to exert a genotoxic effect reducing both the replication index and mitotic index.     

Heterologous Expression in Remodeled C. elegans: A Platform for Monoaminergic Agonist Identification and Anthelmintic Screening

Monoamines, such as 5-HT and tyramine (TA), paralyze both free-living and parasitic nematodes when applied exogenously and serotonergic agonists have been used to clear Haemonchus contortus infections in vivo. Since nematode cell lines are not available and animal screening options are limited, we have developed a screening platform to identify monoamine receptor agonists. Key receptors were expressed heterologously in chimeric, genetically-engineered Caenorhabditis elegans, at sites likely to yield robust phenotypes upon agonist stimulation. This approach potentially preserves the unique pharmacologies of the receptors, while including nematode-specific accessory proteins and the nematode cuticle. Importantly, the sensitivity of monoamine-dependent paralysis could be increased dramatically by hypotonic incubation or the use of bus mutants with increased cuticular permeabilities. We have demonstrated that the monoamine-dependent inhibition of key interneurons, cholinergic motor neurons or body wall muscle inhibited locomotion and caused paralysis. Specifically, 5-HT paralyzed C. elegans 5-HT receptor null animals expressing either nematode, insect or human orthologues of a key Gα_o-coupled 5-HT₁-like receptor in the cholinergic motor neurons. Importantly, 8-OH-DPAT and PAPP, 5-HT receptor agonists, differentially paralyzed the transgenic animals, with 8-OH-DPAT paralyzing mutant animals expressing the human receptor at concentrations well below those affecting its C. elegans or insect orthologues. Similarly, 5-HT and TA paralyzed C. elegans 5-HT or TA receptor null animals, respectively, expressing either C. elegans or H. contortus 5-HT or TA-gated Cl^- channels in either C. elegans cholinergic motor neurons or body wall muscles. Together, these data suggest that this heterologous, ectopic expression screening approach will be useful for the identification of agonists for key monoamine receptors from parasites and could have broad application for the identification of ligands for a host of potential anthelmintic targets.     

Antimutagenic activity of soybeans fermented with basidiomycetes in Ames/Salmonella test

Soybeans fermented with either Phellinus igniarius or Agrocybe cylindracea inhibited the mutagenicity of the directly-acting mutagens: 4-nitro-o-phenylenediamine on Salmonella typhimurium strain TA 98 and NaN₃ on S. typhimurium strain TA 100; and indirectly-acting mutagens, 2-aminofluorene using strain TA 98 and benzo[a]pyrene using strain TA 100, in the presence of a supernatant solution from mammalian hepatic microsomes.     

Measurement of drug-metabolizing systems in Salmonella typhimurium strains G46, TA1535, TA100, TA1538 and TA98

Salmonella typhimurium strains which are commonly used in the Ames test for screening potential carcinogens were examined for a number of drug-metabolizing systems. Neither cytochrome P-450 itself nor two activities catalyzed by the cytochrome P-450 system in mammalian cells, i.e., benzpyrene monooxygenase and ethoxycoumarin O-deethylation, could be detected. Nor do these bacterial strains demonstrate any ability to detoxify epoxides by hydrating them or to conjugate p-nitrophenol with glucuronic acid.On the other hand, S. typhimurium strains G46, TA1535, TA100, TA1538 and TA98 contain considerable amounts of acid-soluble thiols, approx. 5–10% of which is glutathione. These bacteria can also enzymatically conjugate glutathione with 1-chloro-2,4-dinitrobenzene (CDNB) and can reduce oxidized glutathione using NADPH as cofactor.Thus, enzymatic and non-enzymatic reaction of immediate carcinogens with thiol groups in S. typhimurium may have a significant effect on the outcome of the Ames test in certain cases.     

Cell wall teichoic acids of Bacillus licheniformis VKM B-511T, Bacillus pumilus VKM B-508T, and other strains previously assigned to Bacillus pumilus

The teichoic acids (TAs) of type strains, viz. Bacillus licheniformis VKM B-511^T and Bacillus pumilus VKM B-508^T, as well as phylogenetically close bacteria VKM B-424, VKM B-1554, and VKM B-711 previously assigned to Bacillus pumilus on the basis of morphological, physiological, and biochemical properties, were investigated. Three polymers were found in the cell wall of each of the 5 strains under study. Strains VKM B-508^T, VKM B-424, and VKM B-1554 contained polymers of the same core: unsubstituted 1,3-poly(glycerol phosphate) (TA I) and 1,3-poly(glycerol phosphate) with O-D-Ala and N-acetyl-??-D-glucosamine substituents (TA II and TA III??, respectively). The cell walls of two remaining strains contained TA I, TA II, and a poly(glycosylpolyol phosphate) with the following structure of repeating units: -6)-??-D-GlcpNAc(1??1)-snGro-(3-P-(TA III?) in ??Bacillus pumilus?? VKM B-711 (100% 16S rRNA gene similarity with the type strain of Bacillus safensis) and -6)-??-D-Galp-(1??2)-snGro-(3-P-(TA III?) in Bacillus licheniformis VKM B-511^T. The simultaneous presence of three different TAs in the cell walls was confirmed by the NMR spectroscopic DOSY methods. The structure of the polymers and localization of O-D-Ala residues were investigated by the chemical and NMR spectroscopic methods.     

Mutagenicity of vinyl chloride,chloroethyleneoxide, chloroacetaldehyde and chloroethanol

Exposure of S. typhimurium strains TA 1530, TA 1535 and G-46 to vinyl chloride increased the number of his⁺ rev./plate 16, 12 or 5 times over the spontaneous mutation rate. The mutagenic response for TA 1530 strain was enhanced 7, 4 or 5-fold when fortified S-9 liver fractions from humans, rats or mice were added. In TA 1530 strain, chloroacetic acid showed only toxic effects, while chloroacetaldehyde, chloroethanol and chloroethyleneoxide caused a mutagenic response. The latter compound was shown to be a strong alkylating agent.     

Studies on the oxidation products from 2,4-diaminotoluene by hydrogen peroxide and their mutagenicities. II.

2,4-Diaminotoluene (DAT) was reacted with hydrogen peroxide at room temperature for 2 days, and the resulting red precipitates were separated into 5 fractions on silica gel column chromatography. On the gas chromatographic (GC) study, the first fraction (Fr. 1), which is mutagenic (1425 and 1391 revertants/μg in the absence and presence of S9 respectively) in Salmonella typhimurium TA98, contained several peaks. Fr. 1 was further separated into 4 subfractions (Fr. 1-I-Fr. 1-IV) by silica gel column chromatography. The red crystals were separated from Fr. 1-III and the structure of the compound was determined to be 1,8-diamino-2,7-dimethylphenazine from physicochemical and chemical evidence.Further, o-nitro-p-toluidine, p-nitro-o-toluidine, 3,3′-diamino-4,4′-dimethylazobenzene and 3,3′ diamino-4,4′-dimethylazoxybenzene were identified with authentic and synthesized samples by gas chromatography/mass spectrometry. These compounds without nitrotoluidines were mutagenic, and phenazine, azo and azoxy compounds induced 49, 301 and 245 revertants/nmole in Salmonella typhimurium TA98 with 25 μl S9 per plate, respectively.     

Antitumor and toxicologic properties of the organometallic anticancer agent vanadocene dichloride

We report here on the antineoplastic, toxicologic, and transmembrane transfer properties of vanadocene dichloride (VDC), a representative metallocene dihalide. VDC is cytotoxic to HEp-2 human epidermoid carcinoma cells, in vitro, in a dose dependent manner, with a D_o value (dose increment reducing the survival fraction by 1/e) of 0.530 ± 0.005 μg/ml. Under similar experimental conditions, the D_o for cisplatin (CDDP) against these cells is 0.46 ± 0.08 μg/ml. In a murine mammary adenocarcinoma (TA3Ha) system, 125 μg/ml VDC inhibits the tumor-forming ability of 10⁵ cells upon i.p. inoculation into syngeneic Strain A mice. The transmembrane transfer rate constants for the metal uptake of VDC and CDDP by TA3Ha cells in vitro were found to be 3.3 ± 0.8 × 10⁻⁴ min⁻¹ and 12 ± 2.0 × 10^t-4 min⁻¹, respectively. In vivo studies with TA3Ha cells show that two i.p. treatments of 20, 40, and 60 mg/kg VDC increase the host survival by 30, 50, and 90%, respectively. Under similar conditions, 2, 4, and 6 mg/kg CDDP (equitoxic dose levels) prolong the host survival 50, 75, and 83%, respectively. Morphological, blood urea nitrogen level, and serum creatinine level data for Strain A mice treated with 60 mg/kg VDC give no evidence of renal or small intestinal damage. However, changes in the liver consistent with fatty cell degeneration are observed in these mice.     

Synthesis, structure and cytotoxicity studies of diisopropylammonium and triethylammonium salts of triphenylphosphinegold(I) sulfanylcarboxylates

Compounds of the type [HQ][Au(PPh₃)(xspa)] and [HP][Au(PPh₃)(xspa)] {HQ = diisopropylammonium; HP = triethylammonium; H₂xspa = 3-aryl-2-sulfanylpropenoic acids [x: p = 3-phenyl-, f = 3-(2-furyl)-, t = 3-(2-thienyl)-, -o-py = 3-(2-pyridyl)-, Clp = 3-(2-chlorophenyl)-, -o-mp = 3-(2-methoxyphenyl)-, -p-mp = 3-(4-methoxyphenyl)-, -o-hp = 3-(2-hydroxyphenyl)-, -p-hp = 3-(4-hydroxyphenyl)-, diBr-o-hp = 3-(3,5-dibromo-2-hydroxyphenyl]} were synthesized and characterized by IR and NMR (¹H, ¹³C and ³¹P) spectroscopy and by FAB mass spectrometry. The structures of [HQ][Au(PPh₃)(Clpspa)] and [HQ][Au(PPh₃)(-o-mpspa)] show that the crystal contains hydrogen-bonded diisopropylammonium cations and [Au(PPh₃)(xspa)]⁻ anions. The anions in the two compounds have different structures, with the carboxylate group either coordinated or not coordinated to the gold atom, respectively. The in vitro antitumour activities against the HeLa-229, A2780 and A2780cis cell lines were determined for all complexes. The diisopropylammonium derivatives were generally found to be more active, in particular against the A2780cis cell line, and showed a high ability to circumvent the cellular resistance to cisplatin.     

Regulation of enzymic oxidation of indole-3-acetic acid by phenols: Structure-activity relationships

Mono- and diphenols were tested for their effects on the decarboxylation of [1-¹⁴C]IAA catalysed by purified horseradish peroxidase (EC 1.11.1.7) in the presence or absence of 2,4-dichlorophenol (DCP). The number of hydroxyl groups and their position relative to each other and the nature and position of other substituents on the aromatic ring were found to affect the activity. Although the effects were complex, the following generalizations may be made. (1) Monophenols produce activation when no other cofactor is present. p-Substituted monophenols are more active than o- or m-compounds. In the presence of DCP, the activity varies from slight activation to strong inhibition. (2) m-Diphenols also produce activation in the absence of other cofactors while o- and p-diphenols, with the exception of 3,4-dihydroxyacetophenone and 3,4-dihydroxypropiophenone, produce strong inhibition in the presence or absence of DCP. The o-diphenolsare degraded in the IAA-oxidizing enzyme system and thus produce only a temporary inhibition. (3) m-Diphenols and 3,4-dihydroxyacetophenone produce a sustained inhibition in the presence of DCP. (4) Substitution at position 2 significantly alters the activity of m-diphenols. (5) O-Methylation alters the activity of most o-diphenols. In the absence of DCP, o-methoxyphenols and certain other phenols such as 3,4-dihydroxyacetophenone and 2,6-dihydroxyacetophenone either promote or inhibit IAA oxidation depending on concentration.     

Development of a bioprocess to convert PET derived terephthalic acid and biodiesel derived glycerol to medium chain length polyhydroxyalkanoate

Sodium terephthalate (TA) produced from a PET pyrolysis product and waste glycerol (WG) from biodiesel manufacture were supplied to Pseudomonas putida GO16 in a fed-batch bioreactor. Six feeding strategies were employed by altering the sequence of TA and WG feeding. P. putida GO16 reached 8.70 g/l cell dry weight (CDW) and 2.61 g/l PHA in 48 h when grown on TA alone. When TA and WG were supplied in combination, biomass productivity (g/l/h) was increased between 1.3- and 1.7-fold and PHA productivity (g/l/h) was increased 1.8- to 2.2-fold compared to TA supplied alone. The monomer composition of the PHA accumulated from TA or WG was predominantly composed of 3-hydroxydecanoic acid. PHA monomers 3-hydroxytetradeeanoic acid and 3-hydroxytetradecenoic acid were not present in PHA accumulated from TA alone but were present when WG was supplied to the fermentation. When WG was either the sole carbon source or the predominant carbon source supplied to the fermentation the molecular weight of PHA accumulated was lower compared to PHA accumulated when TA was supplied as the sole substrate. Despite similarities in data for the properties of the polymers, PHAs produced with WG present in the PHA accumulation phase were tacky while PHA produced where TA was the sole carbon substrate in the polymer accumulation phase exhibited little or no tackiness at room temperature. The co-feeding of WG to fermentations allows for increased utilisation of TA. The order of feeding of WG and TA has an effect on TA utilisation and polymer properties.     

Identification and characterization of a HEPN-MNT family type II toxin–antitoxin in Shewanella oneidensis

Toxin–antitoxin (TA) systems are prevalent in bacteria and archaea. However, related studies in the ecologically and bioelectrochemically important strain Shewanella oneidensis are limited. Here, we show that SO_3166, a member of the higher eukaryotes and prokaryotes nucleotide-binding (HEPN) superfamily, strongly inhibited cell growth in S. oneidensis and Escherichia coli. SO_3165, a putative minimal nucleotidyltransferase (MNT), neutralized the toxicity of SO_3166. Gene SO_3165 lies upstream of SO_3166, and they are co-transcribed. Moreover, the SO_3165 and SO_3166 proteins interact with each other directly in vivo, and antitoxin SO_3165 bound to the promoter of the TA operon and repressed its activity. Finally, the conserved Rx4-6H domain in HEPN family was identified in SO_3166. Mutating either the R or H abolished SO_3166 toxicity, confirming that Rx4-6H domain is critical for SO_3166 activity. Taken together, these results demonstrate that SO_3166 and SO_3165 in S. oneidensis form a typical type II TA pair. This TA pair plays a critical role in regulating bacterial functions because its disruption led to impaired cell motility in S. oneidensis. Thus, we demonstrated for the first time that HEPN-MNT can function as a TA system, thereby providing important insights into the understanding of the function and regulation of HEPNs and MNTs in prokaryotes.     

A new structural alert for benzimidazoles: 2,6-dimethylphenyl substituents increase mutagenic potential and time-dependent CYP3A4 inhibition risk

A series of 2-[(2,6)-dimethylphenyl]benzimidazole analogs displayed strong potential for mutagenicity following metabolic activation in either TA98 or TA100 Salmonella typhimurium strains. The number of revertants was significantly reduced by replacing the 2,6-dimethylphenyl group with a 2,6-dichlorophenyl moiety. Time-dependent CYP3A4 inhibition was also observed with a compound containing a 2-[(2,6)-dimethylphenyl] benzimidazole ring, implying risk for this scaffold to generate reactive metabolites.     

Altering toluene 4-monooxygenase by active-site engineering for the synthesis of 3-methoxycatechol, methoxyhydroquinone, and methylhydroquinone

Wild-type toluene 4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 oxidizes toluene to p-cresol (96%) and oxidizes benzene sequentially to phenol, to catechol, and to 1,2,3-trihydroxybenzene. In this study T4MO was found to oxidize o-cresol to 3-methylcatechol (91%) and methylhydroquinone (9%), to oxidize m-cresol and p-cresol to 4-methylcatechol (100%), and to oxidize o-methoxyphenol to 4-methoxyresorcinol (87%), 3-methoxycatechol (11%), and methoxyhydroquinone (2%). Apparent V_max values of 6.6 ± 0.9 to 10.7 ± 0.1 nmol/min/ mg of protein were obtained for o-, m-, and p-cresol oxidation by wild-type T4MO, which are comparable to the toluene oxidation rate (15.1 ± 0.8 nmol/min/mg of protein). After these new reactions were discovered, saturation mutagenesis was performed near the diiron catalytic center at positions I100, G103, and A107 of the alpha subunit of the hydroxylase (TmoA) based on directed evolution of the related toluene o-monooxygenase of Burkholderia cepacia G4 (K. A. Canada, S. Iwashita, H. Shim, and T. K. Wood, J. Bacteriol. 184:344-349, 2002) and a previously reported T4MO G103L regiospecific mutant (K. H. Mitchell, J. M. Studts, and B. G. Fox, Biochemistry 41:3176-3188, 2002). By using o-cresol and o-methoxyphenol as model substrates, regiospecific mutants of T4MO were created; for example, TmoA variant G103A/A107S produced 3-methylcatechol (98%) from o-cresol twofold faster and produced 3-methoxycatechol (82%) from 1 mM o-methoxyphenol seven times faster than the wild-type T4MO (1.5 ± 0.2 versus 0.21 ± 0.01 nmol/min/mg of protein). Variant I100L produced 3-methoxycatechol from o-methoxyphenol four times faster than wild-type T4MO, and G103S/A107T produced methylhydroquinone (92%) from o-cresol fourfold faster than wild-type T4MO and there was 10 times more in terms of the percentage of the product. Variant G103S produced 40-fold more methoxyhydroquinone from o-methoxyphenol than the wild-type enzyme produced (80 versus 2%) and produced methylhydroquinone (80%) from o-cresol. Hence, the regiospecific oxidation of o-methoxyphenol and o-cresol was changed for significant synthesis of 3-methoxycatechol, methoxyhydroquinone, 3-methylcatechol, and methylhydroquinone. The enzyme variants also demonstrated altered monohydroxylation regiospecificity for toluene; for example, G103S/A107G formed 82% o-cresol, so saturation mutagenesis converted T4MO into an ortho-hydroxylating enzyme. Furthermore, G103S/A107T formed 100% p-cresol from toluene; hence, a better para-hydroxylating enzyme than wild-type T4MO was formed. Structure homology modeling suggested that hydrogen bonding interactions of the hydroxyl groups of altered residues S103, S107, and T107 influence the regiospecificity of the oxygenase reaction.     

Effect of Phloroglucinol and Resorcinol on the Clingstone Peach Polyphenol Oxidase-catalyzed Oxidation of 4-Methylcatechol

Phloroglucinol and resorcinol are not substrates for clingstone peach (Prunus persica) polyphenol oxidase, but they react with 4-methyl-o-quinone, produced either enzymatically or nonenzymatically, to give an intense red or red-brown color with a maximal absorption at about 470 nanometers. Several colored products were isolated from an ethyl acetate extract of the reaction by two-dimensional thin layer chromatography. Based on thin layer chromatographic and spectral studies of the enzymatic and nonenzymatic reactions, polyphenol oxidase does not play a role in the reaction between 4-methyl-o-quinone and phloroglucinol, resorcinol, d-catechin, or orcinol. In such reactions, the function of polyphenol oxidase is the formation of 4-methyl-o-quinone which then reacts nonenzymatically with the above phenols. Activation energies of both enzymatic and nonenzymatic reactions were determined.     

UKEMS trial: Bacterial mutation tests of 4-chloromethylbiphenyl, 4-hydroxymethylbiphenyl,and benzyl chloride,using E. coli WP2uvrA(pKM101) and S. typhimurium TA98 and TA100

4CMB, 4HMB and BC were assayed in plate tests, using E. coli WP2uvrA(pKM101), and S. typhimurium TA98 and TA100, in the presence or absence of microsomal activation. 4CMB was also assayed in fluctuation tests using E. coli WP2uvrA(pKM101). 4HMB was uniformly negative, and 4CMB was mutagenic to all 3 strains. BC was negative in TA98 and positive in TA100 and WP2uvrA(pKM101). The presence or absence of S9 made no substantial difference to the mutagenicity of 4CMB or BC.     

Leucine aminopeptidase (bovine lens): Synthesis and kinetic properties of ortho-, meta-, and para-substituted leucyl-anilides

The synthesis of a number of leucyl derivatives of substituted anilides and their properties as substrates and inhibitors of Zn²⁺-Mg²⁺ leucine aminopeptidase (EC 3.4.11.1) at pH 8.5 and 30 °C are described. The compounds include leucyl-X where X is o-, m-, or p-aminobenzenesulfonic acid, o-, m-, or p-anisidine, and m- or p-aminobenzenesulfonyl fluoride. The latter two sulfonyl fluorides, designed to be active site-directed irreversible inhibitors, turned out to be good substrates for leucine aminopeptidase. The K_m and V values of the above compounds as substrates for leucine aminopeptidase are reported. N-Leucyl-m-aminobenzenesulfonate exhibits desirable properties (solubility much greater than K_m, Δ? at 295 nm of 2000 m^?1 cm^?1, and V of 300 μmol min^?1 mg^?1) as a substrate for a spectrophotometric assay of leucine aminopeptidase. With the exception of N-leucyl-p-aminobenzenesulfonate, all of the above compounds are inhibitors of the hydrolysis of leucyl-p-nitroanilide by leucine aminopeptidase with K_i values approximately their K_m values when they are used as substrates. Despite wide variability in steric bulk, chemical composition, and electrical charge of the substituted anilides, the K_m values of the above compounds vary over a narrow range (0.5 to 4.8 mm), which indicates that the leucyl moiety plays the predominant role in the determination of K_m values. Although the K_m values of m- substituents are similar to those of o- substituents, the V values for m-substituents are much greater than those for o- substituents, which suggests that o-substituents interfere with the catalytic process. N-Leucyl-p-aminobenzenesulfonate and N-alanyl-p-aminobenzenesulfonate as well as the nonsubstrate p-aminobenzenesulfonate stimulate rather than inhibit the proteolysis of leucyl-p-nitroanilide. The stimulation has no effect on V but lowers the K_m for the hydrolysis of leucyl-p-nitroanilide, which is compatible with these compounds' serving as nonessential activators.     

Detection of mutagenicity of diphenyl ether herbicides in Salmonella typhimurium YG1026 and YG1021

Three kinds of diphenyl ether herbicides, 4-nitrophenyl 2,4,6-trichlorophenyl ether (CNP, chlornitrofen), 2,4-dichlorophenyl 3-methoxy-4-nitrophenyl ether (chlomethoxynil) and 2,4-dichlorophenyl 3-methoxycarbonyl-4-nitrophenyl ether (bifenox), were tested for mutagenicity in Salmonella typhimurium YG1026 and YG1021, which have high nitroreductase activity, and also in S. typhimurium TA100 and TA98. CNP and chlomethoxynil showed mutagenicity in S. typhimurium YG1026, without S9 mix, inducing 50 and 304 revertants per μg. These mutagenicities were suppressed by the addition of S9 mix. CNP and chlomethoxynil were also mutagenic to YG1021 with and without S9 mix, and their mutagenicities were lower than those to YG1026. On the other hand, bifenox was mutagenic to YG1026 only with S9 mix, inducing 3.0 revertants per μg. These three herbicides showed no mutagenicity in S. typhimurium TA100 and TA98 either with or without S9 mix.     

Construction of a Symbiotically Effective Strain of Rhizobium leguminosarum bv. trifolii with Increased Nodulation Competitiveness

Genes involved in nodulation competitiveness (tfx) were inserted by marker exchange into the genome of the effective strain Rhizobium leguminosarum bv. trifolii TA1. Isogenic strains of TA1 were constructed which differed only in their ability to produce trifolitoxin, an antirhizobial peptide. Trifolitoxin production by the ineffective strain R. leguminosarum bv. trifolii T24 limited nodulation of clover roots by trifolitoxin-sensitive strains of R. leguminosarum bv. trifolii. The trifolitoxin-producing exconjugant TA1::10-15 was very competitive for nodulation on clover roots when coinoculated with a trifolitoxin-sensitive reference strain. The nonproducing exconjugant TA1::12-10 was not competitive for nodule occupancy when coinoculated with the reference strain. Tetracycline sensitivity and Southern analysis confirmed the loss of vector DNA in the exconjugants. Trifolitoxin production by TA1::10-15 was stable in the absence of selection pressure. Transfer of tfx to TA1 did not affect nodule number or nitrogenase activity. These experiments represent the first stable genetic transfer of genes involved in nodulation competitiveness to a symbiotically effective Rhizobium strain.