RESUMO
Ethylene acts as an inhibitor of the nodulation process of leguminous plants. However, some bacteria can decrease deleterious ethylene levels by the action of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase which degrades ACC, the ethylene precursor in all higher plants. Co-inoculation of rhizobia with endophytes enhances the rhizobial symbiotic efficiency with legumes, improving both nodulation and nitrogen fixation. However, not much is understood about the mechanisms employed by these endophytic bacteria. In this regard, the role of ACC deaminase from endophytic strains in assisting rhizobia in this process has yet to be confirmed. In this study, the role of ACC deaminase in an endophyte's ability to increase Rhizobium tropici nodulation of common bean was evaluated. To assess the effect of ACC deaminase in an endophyte's ability to promote rhizobial nodulation, the endophyte Serratia grimesii BXF1, which does not encode ACC deaminase, was transformed with an exogenous acdS gene. The results obtained indicate that the ACC deaminase-overexpressing transformant strain increased common bean growth, and enhanced the nodulation abilities of R. tropici CIAT899, in both cases compared to the wild-type non-transformed strain. Furthermore, plant inoculation with the ACC deaminase-overproducing strain led to an increased level of plant protection against a seed-borne pathogen. SIGNIFICANCE AND IMPACT OF THE STUDY: In this work, we studied the effect of ACC deaminase production by the bacterial endophyte Serratia grimesi BXF1, and its impact on the nodulation process of common bean. The results obtained indicate that ACC deaminase is an asset to the synergetic interaction between rhizobia and the endophyte, positively contributing to the overall legume-rhizobia symbiosis by regulating inhibitory ethylene levels that might otherwise inhibit nodulation and overall plant growth. The use of rhizobia together with an ACC deaminase-producing endophyte is, therefore, an important strategy for the development of new bacterial inoculants with increased performance.
Assuntos
Proteínas de Bactérias/metabolismo , Carbono-Carbono Liases/metabolismo , Phaseolus/crescimento & desenvolvimento , Nodulação/fisiologia , Rhizobium tropici/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Serratia/enzimologia , Inoculantes Agrícolas , Endófitos/metabolismo , Etilenos/metabolismo , Phaseolus/microbiologia , Serratia/genética , Serratia/metabolismo , SimbioseRESUMO
It has been reported that PGPB, containing ACC deaminase, can cleave the plant ethylene precursor ACC and thereby lower ethylene concentration in a developing or stressed plant, protecting it against the deleterious effects of stress ethylene and facilitating the formation of longer roots. In a previous work we have demonstrated expression of the ACC deaminase gene ( acdS) from Enterobacter cloacae UW4 under the control of the lac promoter in Azospirillum brasilense Cd. With the inference that a construct including the ACC deaminase gene under the control of a constitutive promoter weaker than the lac promoter might impose less metabolic load on Azospirillum and improve its fitness, it was decided to clone acdS under the control of a tetracycline resistance gene promoter. The ACC deaminase structural gene was fused to the Tet(r) gene promoter by overlap extension using PCR, cloned in pRK415, and transferred into A. brasilense Cd. The resulting transformants showed lower ACC deaminase activity than those with the lac promoter controlled acdS gene. However, acdS under the control of the Tet(r) gene promoter imposed lesser metabolic load on Azospirillum brasilense Cd. The result was significantly increased IAA synthesis and greater bacterial growth rate, as well as increased ability to survive on the surface of tomato leaves and to promote the growth of tomato seedlings.
Assuntos
Azospirillum brasilense/genética , Azospirillum brasilense/fisiologia , Carbono-Carbono Liases/genética , Regiões Promotoras Genéticas/genética , Transformação Bacteriana , Azospirillum brasilense/ultraestrutura , Contagem de Colônia Microbiana , Primers do DNA , Enterobacter cloacae/genética , Solanum lycopersicum/fisiologia , Microscopia Eletrônica de Varredura , Proteínas Repressoras/genética , Microbiologia do SoloRESUMO
The ACC deaminase structural gene (acdS) from Enterobacter cloacae UW4 was cloned in the broad host range plasmid pRK415 under the control of the lac promoter and transferred into Azospirillum brasilense Cd and Sp245. A. brasilenseCd and Sp245 transformants showed high ACC deaminase activity, similar to that observed in Enterobacter cloacae UW4. The expression of ACC deaminase improved the existing growth promoting activity of Azospirillum. The roots of tomato and canola seedlings were significantly longer in plants inoculated with A. brasilense Cd transformants than those in plants inoculated with the nontransformed strains of the same bacterium. In the case of wheat seedlings, inoculation with A. brasilense Cd transformants did not promote root growth. The difference in plant response (canola and tomato versus wheat) is attributed to the greater sensitivity of canola and tomato plants to ethylene as compared to wheat plants.
RESUMO
A genomic library from Burkholderia cepacia IS-16 was constructed in Escherichia coli by partial Sau3AI digestion of the chromosomal DNA, with the plasmid vector Bluescript SK. This library was screened for clones able to grow as green stained colonies on selective medium developed for detecting phosphatase-positive colonies. Three green-stained clones (pFS1, pFS2, and pFS3) carried recombinant plasmids harboring DNA inserts of 5.0, 8.0, and 0.9 kb, respectively. DNA hybridization experiments demonstrated the presence of overlapping DNA fragments in the three clones and that these three clones were all derived from Burkholderia cepacia IS-16 genomic DNA. DNA sequence analysis, together with polyacrylamide gels of proteins encoded by E. coli containing pFS3, suggested that the isolated 0. 9-kb DNA fragment encodes the functional portion of a phosphate transport protein.
Assuntos
Proteínas da Membrana Bacteriana Externa/genética , Burkholderia cepacia/genética , Genes Bacterianos , Monoéster Fosfórico Hidrolases/genética , Sequência de Aminoácidos , Sequência de Bases , Burkholderia cepacia/enzimologia , Escherichia coli/genética , Biblioteca Gênica , Vetores Genéticos , Dados de Sequência Molecular , PlasmídeosRESUMO
Hypotonia was the initial symptom in four siblings from a nonconsanguineous Tunisian-Jewish family. Plasma carnitine was severely deficient, and urinary organic acid analysis revealed increased excretion of 3-hydroxyisovaleric acid and 3-methylcrotonylglycine. 3-Methylcrotonyl-coenzyme A carboxylase activity was reduced in skin fibroblasts; pyruvate carboxylase and serum biotinidase activities were normal. We conclude that 3-methylcrotonyl-coenzyme A carboxylase deficiency should be added to the list of metabolic causes of familial hypotonia of childhood.
Assuntos
Carbono-Carbono Ligases , Ligases/deficiência , Hipotonia Muscular/genética , Carnitina/uso terapêutico , Criança , Pré-Escolar , Feminino , Humanos , Ligases/metabolismo , Masculino , Hipotonia Muscular/tratamento farmacológico , Hipotonia Muscular/enzimologia , Piruvato Carboxilase/metabolismoRESUMO
Four very-low-birth-weight infants developed localized intestinal perforations after enteral administration of indomethacin. The clinical picture and histologic findings were unlike those seen in necrotizing enterocolitis.