RESUMO
The objective of the present study was to examine a biological model under greenhouse conditions for the bioremediation of atrazine contaminated soils. The model consisted in a combination of phytoremediation (using Phaseolus vulgaris L.) and rhizopheric bio-augmentation using native Trichoderma sp., and Rhizobium sp. microorganisms that showed no inhibitory growth at 10,000 mg L-1 of herbicide concentration. 33.3 mg of atrazine 50 g-1 of soil of initial concentration was used and an initial inoculation of 1 × 109 UFC mL-1 of Rhizobium sp. and 1 × 105 conidia mL-1 of Trichoderma sp. were set. Four treatments were arranged: Bean + Trichoderma sp. (B+T); Bean + Rhizobium sp. (BR); Bean + Rhizobium sp. + Trichoderma sp. (B+R+T) and Bean (B). 25.51 mg of atrazine 50 g-1 of soil (76.63%) was removed by the B+T treatment in 40 days (a = 0.050, Tukey). This last indicate that the proposed biological model and methodology developed is useful for atrazine contaminated bioremediation agricultural soils, which can contribute to reduce the effects of agrochemical abuse.
Assuntos
Atrazina/metabolismo , Biodegradação Ambiental , Consórcios Microbianos , Phaseolus/fisiologia , Poluentes do Solo/metabolismo , Agricultura , Atrazina/análise , Herbicidas/análise , Herbicidas/metabolismo , México , Modelos Biológicos , Phaseolus/efeitos dos fármacos , Rhizobium/efeitos dos fármacos , Rhizobium/metabolismo , Rizosfera , Microbiologia do Solo , Poluentes do Solo/análise , Trichoderma/efeitos dos fármacos , Trichoderma/metabolismoRESUMO
The aim of this study was to evaluate the diversity of rhizobial isolates obtained from root nodules of pigeonpea plants grown at the eastern edge of the Brazilian Pantanal. The bacterial isolates were isolated from root nodules from field-growing pigeonpea grown in two rural settlements of the Aquidauana municipality. The bacterial isolates were characterized phenotypically by means of cultural characterization, intrinsic antibiotic resistance (IAR), salt and high incubation temperature tolerance, and amylolytic and cellulolytic activities. The molecular characterization of the bacterial isolates was carried out using amplified ribosomal DNA restriction analysis (ARDRA) and Box-polymerase chain reaction (PCR) techniques. In addition, the symbiotic performance of selected rhizobial isolates was evaluated in a greenhouse experiment using sterile substrate. The phenotypic characterization revealed that the bacterial strains obtained from pigeonpea root nodules presented characteristics that are uncommon among rhizobial isolates, indicating the presence of new species nodulating the pigeonpea plants in the Brazilian Pantanal. The molecular fingerprinting of these bacterial isolates also showed a highly diverse collection, with both techniques revealing less than 25% similarity among bacterial isolates. The evaluation of symbiotic performance also indicated the presence of microorganisms with high potential to increase the growth and nitrogen content at the shoots of pigeonpea plants. The results obtained in this study indicate the presence of a highly diversified rhizobial community nodulating the pigeonpea at the eastern edge of the Brazilian Pantanal.
Assuntos
Cajanus/microbiologia , Fenótipo , Rhizobium/genética , Antibacterianos/farmacologia , Brasil , Impressões Digitais de DNA , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Rhizobium/efeitos dos fármacos , Rhizobium/isolamento & purificação , Análise de Sequência de DNARESUMO
Nitrogen-limited conditions are considered to be a prerequisite for legume-rhizobial symbiosis, but the effects of nitrate-rich conditions on symbiotic status remain poorly understood. We addressed this issue by examining rhizobial (Rhizobim tropici) and arbusclar mycorrhizal (Glomus intraradices) symbiosis in Phaseolus vulgaris L. cv. Negro Jamapa under nitrate pre-incubation and continuous nitrate conditions. Our results indicate that nitrate pre-incubation, independent of the concentration, did not affect nodule development. However, the continuous supply of nitrate at high concentrations impaired nodule maturation and nodule numbers. Low nitrate conditions, in addition to positively regulating nodule number, biomass, and nitrogenase activity, also extended the span of nitrogen-fixing activity. By contrast, for arbuscular mycorrhizae, continuous 10 and 50 mmol/L nitrate increased the percent root length colonization, concomitantly reduced arbuscule size, and enhanced ammonia transport without affecting phosphate transport. Therefore, in this manuscript, we have proposed the importance of nitrate as a positive regulator in promoting both rhizobial and mycorrhizal symbiosis in the common bean.
Assuntos
Micorrizas/fisiologia , Nitratos/farmacologia , Phaseolus/microbiologia , Phaseolus/fisiologia , Rhizobium/fisiologia , Simbiose/efeitos dos fármacos , Compostos de Amônio/metabolismo , Biomassa , Tamanho Celular/efeitos dos fármacos , Contagem de Colônia Microbiana , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Proteínas de Membrana Transportadoras/genética , Proteínas de Membrana Transportadoras/metabolismo , Micorrizas/efeitos dos fármacos , Fixação de Nitrogênio/efeitos dos fármacos , Fixação de Nitrogênio/genética , Nitrogenase/metabolismo , Phaseolus/efeitos dos fármacos , Phaseolus/genética , Fenótipo , Fósforo/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Brotos de Planta/efeitos dos fármacos , Brotos de Planta/crescimento & desenvolvimento , Rhizobium/efeitos dos fármacos , Rhizobium/crescimento & desenvolvimento , Nódulos Radiculares de Plantas/efeitos dos fármacos , Nódulos Radiculares de Plantas/fisiologia , Simbiose/genéticaRESUMO
The electrospinning technique of rhizobia immobilization in nanofibres is an innovative and promising alternative for reducing the harmful effects of environmental stress on bacteria strains in a possible inoculant nanotechnology product for use in agriculture. The use of polyvinyl alcohol (PVA) shows up as an effective polymer in cell encapsulation because of its physical characteristics, such as viscosity and power of scattering. The aim of these studies has been to evaluate the survival of rhizobia incorporated in PVA nanofibres, which were applied to soybean seed and then subjected to different storage times and exposure to fungicide. The maintenance of the symbiotic characteristics of the incorporated bacterial strains was also evaluated, noting the formation of nodules in the soybean seedlings. No significant differences in the cell survival at 0 h and after 24 h of storage were observed. After 48 h, a significant difference in the bacterial cell concentration of the seeds affixed with PVA nanofibres was observed. Exposure to the fungicide decreased the viability of the bacteria strains even when coated with the nanofibres. A larger number of nodules formed in soybean seedlings from seeds inoculated with rhizobia incorporated in PVA nanofibres than from seeds inoculated with rhizobia without PVA. Thus, the electrospinning technique is a great alternative to the usual protector inoculants because of its unprecedented capacity to control the release of bacteria.
Assuntos
Glycine max/microbiologia , Nanofibras , Álcool de Polivinil , Rhizobium/fisiologia , Sementes/microbiologia , Fungicidas Industriais/farmacologia , Nanofibras/química , Álcool de Polivinil/química , Rhizobium/efeitos dos fármacos , Nódulos Radiculares de Plantas/microbiologia , Plântula/microbiologiaRESUMO
Rhizobial surface polysaccharides (SPS) are, together with nodulation (Nod) factors, recognized as key molecules for establishment of rhizobia-legume symbiosis. In Rhizobium tropici, an important nitrogen-fixing symbiont of common bean (Phaseolus vulgaris L.), molecular structures and symbiotic roles of the SPS are poorly understood. In this study, Rhizobium sp. strain PRF 81 genes, belonging to the R. tropici group, were investigated: lpxA and lpxE, involved in biosynthesis and modification of the lipid-A anchor of lipopolysaccharide (LPS), and rkpI, involved in synthesis of a lipid carrier required for production of capsular polysaccharides (KPS). Reverse transcription quantitative PCR (RT-qPCR) analysis revealed, for the first time, that inducers released from common bean seeds strongly stimulated expression of all three SPS genes. When PRF 81 cells were grown for 48 h in the presence of seed exudates, twofold increases (p < 0.05) in the transcription levels of lpxE, lpxA, and rkpI genes were observed. However, higher increases (p < 0.05) in transcription rates, about 50-fold for lpxE and about 30-fold for lpxA and rkpI, were observed after only 5 min of incubation with common bean seed exudates. Evolutionary analyses revealed that lpxA and lpxE of PRF81 and of the type strain of R. tropici CIAT899(T)clustered with orthologous Rhizobium radiobacter and were more related to R. etli and Rhizobium leguminosarum, while rkpI was closer to the Sinorhizobium sp. group. Upregulation of lpxE, lpxA, and rkpI genes suggests that seed exudates can modulate production of SPS of Rhizobium sp. PRF81, leading to cell wall changes necessary for symbiosis establishment.
Assuntos
Genes Bacterianos/genética , Phaseolus/química , Exsudatos de Plantas/farmacologia , Polissacarídeos Bacterianos/biossíntese , Rhizobium/genética , Sementes/química , Simbiose/efeitos dos fármacos , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Filogenia , Polissacarídeos Bacterianos/genética , Rhizobium/efeitos dos fármacos , Simbiose/genéticaRESUMO
One of the most cultivated and consumed vegetables in Brazil is the common bean, Phaseolus vulgaris L. The symbiosis of this plant species with nitrogen-fixing bacteria that are adapted to the stresses commonly found in tropical soils can increase production. The aim of this study was to evaluate the symbiotic effectiveness of bacterial strains from soils under different land uses in the Amazon region. Further, rhizobia tolerance to acidity and aluminium and the involvement of some possible physiological mechanisms of such tolerance were also investigated. In assessing the efficiency of biological nitrogen fixation, inoculation with strains UFLA04-195, UFLA04-173 and UFLA04-202, belonging to the genus Rhizobium, resulted in greater plant growth, higher shoot nitrogen content and good nodulation compared to the inoculation with the strain CIAT 899 (R. tropici), and to the mineral nitrogen control or Burkholderia fungorum strains that nodulated or not bean plants. These efficient strains grew better at pH 5.0 than at pH 6.0 or pH 6.9; they also tolerated up to 1 mmol l(-1) of Al(3+) and showed an increased production of exopolysaccharides where the growing rates were less (pH 6.0 and pH 6.9). With respect to aluminium, the highest production of EPS produced greater tolerance to this element. Taken together, these results indicate that the strains evaluated in this study were tolerant to acidity and aluminium; they appeared to have developed resistance mechanisms such as EPS production and a resistant cell outer membrane (indicated by resistance to polymyxin and methyl violet). As these strains also gave increased yields of the host species, further studies on whether to recommend these strains as inoculants are already underway.
Assuntos
Ácidos/toxicidade , Alumínio/toxicidade , Tolerância a Medicamentos , Phaseolus/microbiologia , Rhizobium/fisiologia , Microbiologia do Solo , Simbiose , Brasil , DNA Bacteriano/química , DNA Bacteriano/genética , Dados de Sequência Molecular , Nitrogênio/análise , Fixação de Nitrogênio , Phaseolus/crescimento & desenvolvimento , Brotos de Planta/química , Rhizobium/classificação , Rhizobium/efeitos dos fármacos , Rhizobium/isolamento & purificação , Análise de Sequência de DNARESUMO
The growth of soybean plants were examined when subjected to three contrasting irradiance levels and to various combinations of nutrient solution Fe and Mn concentrations. Two Rhizobium-nodulated soybean genotypes (PI 227557 and Biloxi), which had been previously found to differ in their growth response to various Fe and Mn solutions, were studied. Both genotypes displayed the poorest growth, nodulation and the lowest chlorophyll and nodule ureide concentration at high irradiance (HI), regardless of the solution Fe and Mn concentrations. However, the genotypes differed under HI in their accumulation of Fe. For solution concentrations greater than 13 microM, PI 227557 accumulated up to 1200 microg Feg(-1) leaf dry wt mainly in the form of ferritin crystals within chloroplasts. In contrast, leaf Fe concentrations in Biloxi only reached 300 microg Feg(-1) dry wt and there were no ferritin crystals. Also, in PI 227557 HI induced more severe distortions in leaf cells and nodule ultrastructure than in Biloxi. Based on its poor growth under HI, PI 227557 could be categorized as an Fe-inefficient genotype prone to undergo photoinhibition at HI, in spite of the ferritin crystals in the chloroplasts. Enhanced growth, nodulation, chlorophyll and ureide concentrations in nodules as well as leaf ureide catabolism occurred in both genotypes grown at moderate irradiance (MI) in Fe solutions from 13 to 60 microM supplied with 20 microM Mn. At low irradiance (LI), plant growth and nodulation were lower than at MI values, but higher than those of plants at HI. Irradiance and solution Fe concentration did not alter leaf Cu and Zn concentration in either genotype, with the higher concentrations of these two elements detected in Biloxi. Solutions with Fe concentrations greater than 100 microM were deleterious for both genotypes at all irradiances. Low Fe and high Mn concentrations in leaves was bound to result in the best growth at HI.
Assuntos
Glycine max/genética , Glycine max/microbiologia , Ferro/farmacologia , Luz , Manganês/farmacologia , Rhizobium/fisiologia , Nódulos Radiculares de Plantas/microbiologia , Biomassa , Clorofila/metabolismo , Genótipo , Ferro/metabolismo , Manganês/metabolismo , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/efeitos da radiação , Folhas de Planta/ultraestrutura , Rhizobium/efeitos dos fármacos , Rhizobium/efeitos da radiação , Nódulos Radiculares de Plantas/efeitos dos fármacos , Nódulos Radiculares de Plantas/efeitos da radiação , Nódulos Radiculares de Plantas/ultraestrutura , Soluções , Glycine max/efeitos dos fármacos , Glycine max/ultraestrutura , Especificidade da Espécie , Técnicas de Cultura de Tecidos , Ureia/metabolismoRESUMO
Previously, we reported finding duplicated fixNOQP operons in Rhizobium etli CFN42. One of these duplicated operons is located in the symbiotic plasmid (fixNOQPd), while the other is located in a cryptic plasmid (fixNOQPf). Although a novel FixL-FixKf regulatory cascade participates in microaerobic expression of both fixNOQP duplicated operons, we found that a mutation in fixL eliminates fixNOQPf expression but has only a moderate effect on expression of fixNOQPd. This suggests that there are differential regulatory controls. Interestingly, only the fixNOQPd operon was essential for symbiotic nitrogen fixation (L. Girard, S. Brom, A. Dávalos, O. Lopez, M. Soberón, and D. Romero, Mol. Plant-Microbe Interact. 13:1283-1292, 2000). Searching for potential candidates responsible for the differential expression, we characterized two fnrN homologs (encoding transcriptional activators of the cyclic AMP receptor protein [CRP]-Fnr family) in R. etli CFN42. One of these genes (fnrNd) is located on the symbiotic plasmid, while the other (fnrNchr) is located on the chromosome. Analysis of the expression of the fnrN genes using transcriptional fusions with lacZ showed that the two fnrN genes are differentially regulated, since only fnrNd is expressed in microaerobic cultures of the wild-type strain while fnrNchr is negatively controlled by FixL. Mutagenesis of the two fnrN genes showed that both genes participate, in conjunction with FixL-FixKf, in the microaerobic induction of the fixNOQPd operon. Participation of these genes is also seen during the symbiotic process, in which mutations in fnrNd and fnrNchr, either singly or in combination, lead to reductions in nitrogen fixation. Therefore, R. etli employs a regulatory circuit for induction of the fixNOQPd operon that involves at least three transcriptional regulators of the CRP-Fnr family. This regulatory circuit may be important for ensuring optimal production of the cbb(3), terminal oxidase during symbiosis.
Assuntos
Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/metabolismo , Grupo dos Citocromos c/biossíntese , Fixação de Nitrogênio/genética , Oxigênio/farmacologia , Rhizobium/genética , Fatores de Transcrição , Sequência de Aminoácidos , Duplicação Gênica , Regulação Bacteriana da Expressão Gênica , Genes Bacterianos , Genes Reguladores , Hemeproteínas/metabolismo , Histidina Quinase , Proteínas de Membrana/biossíntese , Modelos Genéticos , Dados de Sequência Molecular , Mutação , Nitrogenase/genética , Nitrogenase/metabolismo , Óperon , Phaseolus/microbiologia , Rhizobium/efeitos dos fármacos , Homologia de Sequência de Aminoácidos , Simbiose/genéticaRESUMO
Alcoholic extracts of seven plants belonging to the Solanaceae family were phytochemically screened and evaluated for their cytotoxic activity by Brine Shrimp Test (BST) with Artemia salina larvae, Inhibition of Cell Division Test (ICDT) on sea urchin Loxechinus albus fertilized eggs and inhibition of crown gall tumors on Potato Disk Bioassay (PDB). From Salpichroa diffusa, bioassay-guided chromatographic separation afforded some active fractions from which epi-katonic acid was identified.
Assuntos
Artemia/efeitos dos fármacos , Medicina Tradicional , Extratos Vegetais/toxicidade , Rhizobium/efeitos dos fármacos , Ouriços-do-Mar/efeitos dos fármacos , Solanaceae , Animais , Feminino , Humanos , Larva/efeitos dos fármacos , Dose Letal Mediana , Masculino , Fitoterapia , Tumores de Planta , Solanum tuberosum , América do SulRESUMO
Jasmonates and salicylic acid are considered to be signal molecules that induce a variety of plant genes involved in wound or defence response, as well as affecting nos promoter activity. In this paper we examined whether these chemicals could also affect nod genes from isogenic rhizobia strains. Isogenic strains contain the Rhizobium leguminosarum nodA promoter fused to the lacZ gene of Escherichia coli and differ only in the source of the regulatory nodD gene. Naringenin, jasmonic acid and methyl jasmonate induced expression of nod genes in strain RBL1284 and salicylic acid showed no activity alone or when used in combination with other compounds; addition of naringenin + jasmonic acid produced a synergistic effect. Results obtained with strain RBL5284 were similar to those for RBL1284 albeit the combination of naringenin with the other compounds markedly inhibited nod gene expression. Whereas RBL5283 responded to naringenin with a strong induction, jasmonic acid, methyl jasmonate or salicylic acid showed no significant responses. The inhibitory effect of salicylic acid on nod gene expression indicates that the induction mechanism of jasmonic acid, methyl jasmonate, N-propyldihydrojasmonate and naringenin is probably different from that of salicylic acid.
Assuntos
Aciltransferases/genética , Ciclopentanos/farmacologia , Regulação Bacteriana da Expressão Gênica/fisiologia , Reguladores de Crescimento de Plantas/farmacologia , Rhizobium/genética , Aciltransferases/biossíntese , Proteínas de Bactérias/genética , Escherichia coli/genética , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Cinética , Oxilipinas , Proteínas Recombinantes de Fusão/biossíntese , Rhizobium/efeitos dos fármacos , Ácido Salicílico/farmacologia , Especificidade da Espécie , beta-Galactosidase/biossíntese , beta-Galactosidase/genéticaAssuntos
Ácido 2,4-Diclorofenoxiacético/toxicidade , Herbicidas/toxicidade , Rhizobium/efeitos dos fármacos , Ácido 2,4-Diclorofenoxiacético/metabolismo , Proteínas de Bactérias/metabolismo , Células Cultivadas , Meios de Cultura , Herbicidas/metabolismo , Metabolismo dos Lipídeos , Ligação Proteica , Rhizobium/metabolismo , Esferoplastos/efeitos dos fármacos , Esferoplastos/metabolismo , Fatores de TempoRESUMO
The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) produced a deleterious effect on the growth of Rhizobium sp. M4, that was reversed by transferring the cells to a fresh control medium. The uptake of 2,4-D by Rhizobium sp. was not affected by chloramphenicol, indicating that it is constitutive rather than inducible. The mechanism of transport also appears to be energy independent, since uptake was not inhibited by azide or arsenate.
Assuntos
Ácido 2,4-Diclorofenoxiacético/farmacologia , Rhizobium/efeitos dos fármacos , Ácido 2,4-Diclorofenoxiacético/metabolismo , Arseniatos/farmacologia , Azidas/farmacologia , Transporte Biológico , Rhizobium/crescimento & desenvolvimento , Rhizobium/metabolismo , Azida SódicaRESUMO
The effects of 1 mM 2,4-Dichlorophenoxyacetic acid on Rhizobium sp. in pure culture was studied. In a previous work it was demonstrated that this herbicide produces an alteration on the saturated to unsaturated phospholipid acyl chains ratio. In the present paper, it was found that this alteration produces a modification on the membrane fluidity in bacteria that had achieved the stationary phase. The same results were obtained when determinations were done in liposomes from sonicated lipids of treated bacteria, indicating that changes in phospholipid acyl chains may be the main cause of membrane fluidity alteration. In addition, it was determined that leucine transport as well as Ca(++)-ATPase activity (a membrane enzyme) was affected under the experimental conditions.
Assuntos
Ácido 2,4-Diclorofenoxiacético/farmacologia , Fluidez de Membrana/efeitos dos fármacos , Rhizobium/efeitos dos fármacos , ATPases Transportadoras de Cálcio/efeitos dos fármacos , ATPases Transportadoras de Cálcio/metabolismo , Glucose/metabolismo , Leucina/metabolismo , Succinatos/farmacocinética , Ácido SuccínicoRESUMO
We have characterized two mutants of Rhizobium meliloti L5-30 obtained by random mutagenesis using Mu-lacZ that were defective in transport of C4-dicarboxylic acids. These mutants induced ineffective nodules on alfalfa. Mutations in the two strains appeared to be located in a dctA gene. Levels of dctA gene expression were determined under different environmental conditions using dctA-lacZ fusions, and beta-galactosidase activities increased in response to osmotic stress and also when the cells were incubated in medium low in calcium. The transcriptional induction of the dctA gene by environmental signals was decreased by DNA gyrase inhibitors such as novobiocin and coumermycin.
Assuntos
Ácidos Dicarboxílicos/metabolismo , Rhizobium/metabolismo , Aminocumarinas , Transporte Biológico Ativo/genética , Cumarínicos/farmacologia , Regulação da Expressão Gênica/efeitos dos fármacos , Mutagênese , Fixação de Nitrogênio/genética , Fixação de Nitrogênio/fisiologia , Novobiocina/farmacologia , Rhizobium/efeitos dos fármacos , Rhizobium/genética , Inibidores da Topoisomerase IIRESUMO
In Pseudomonas aeruginosa and Rhizobium meliloti several choline derivatives, utilized as the sole carbon and nitrogen source, increase acid phosphatase activity. The enzyme activity of both bacteria could be released into the surrounding medium by EDTA-lysozyme treatment. The R. meliloti acid phosphatase activity of crude periplasmic extracts measured with p-nitrophenylphosphate was not inhibited by the presence of 5 mM choline, betaine, trimethylammonium or phosphorylcholine. The activity could not be detected using phosphorylethanolamine or phosphorylcholine as substrates. Among several phosphoesters tested only pyridoxal-5-phosphate was hydrolyzed at a considerable rate. In 7.5% polyacrylamide slab gel electrophoresis (non-denaturing conditions) of crude extracts obtained from bacteria grown in the presence of serine, glutamate, aspartate or dimethylglycine a phosphatase activity with identical mobility could be detected with alpha-naphthylphosphate or pyridoxal-5-phosphate were used as substrates. In conclusion, although the choline metabolites are capable of increasing acid phosphatase activities in R. meliloti and in P. aeruginosa, there are two different enzymes involved, apparently in different metabolisms.
Assuntos
Fosfatase Ácida/metabolismo , Colina/farmacologia , Pseudomonas aeruginosa/enzimologia , Rhizobium/enzimologia , Atropina/metabolismo , Atropina/farmacologia , Betaína/metabolismo , Betaína/farmacologia , Colina/metabolismo , Meios de Cultura , Fosforilcolina/metabolismo , Fosforilcolina/farmacologia , Pseudomonas aeruginosa/efeitos dos fármacos , Compostos de Amônio Quaternário/metabolismo , Compostos de Amônio Quaternário/farmacologia , Rhizobium/efeitos dos fármacos , Sarcosina/análogos & derivados , Sarcosina/metabolismo , Sarcosina/farmacologiaRESUMO
The effect of various salts on the growth and N2-ase activity of Azospirillum brasilense was tested. Bicarbonate was found to be the most toxic, followed by chlorides and sulphate. Tolerance of A. brasilense to these salts was comparable to that of many species of Rhizobium. SO4-- was stimulatory to growth and N2-ase activity up to 40 meq. The process of N2-fixation (N2-ase activity) was found to be more sensitive to all the salts tested as compared to growth.
Assuntos
Bactérias/crescimento & desenvolvimento , Bactérias/efeitos dos fármacos , Bicarbonatos/farmacologia , Cloretos/farmacologia , Resistência Microbiana a Medicamentos , Fixação de Nitrogênio , Rhizobium/efeitos dos fármacos , Rhizobium/crescimento & desenvolvimento , Sulfatos/farmacologiaRESUMO
Specific nitrogenase activity in Azospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C2H4 X mg protein -1 X h-1 to 400 nmol C2H4 by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O2, nitrogenase activity is slightly reduced by the addition of 1-0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce 14CO2 from [U-14C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found with Klebsiella pneumoniae K 11 after addition of 1 mM phenol. However, in Rhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With this Rhizobium japonicum strain significant quantities of phenol (25 mumol in 24 h by 2 X 10(12) cells) were metabolized to 14CO2, with phenol as sole carbon source. With Azospirillum brasilense in liquid culture under 1% and 2% O2 in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.