RESUMO
The aim of this study was to explore the diversity of culturable bacterial communities residing in blackberry plants (Rubus fruticosus). Bacterial endophytes were isolated from plant roots, and their 16S rDNA sequences were amplified and sequenced. Our results show that the roots of R. fruticosus exhibit low colony forming units of bacterial endophytes per gram of fresh tissue (6 x 102 ± 0.5 x 102). We identified 41 endophytic bacterial species in R. fruticosus by BLAST homology search and a subsequent phylogenetic analysis, belonging to the classes Actinobacteria, Bacilli, Alfaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Predominantly, genera belonging the Proteobacteria (Burkholderia, 29.4%; Herbaspirillum, 10.7%; Pseudomonas, 4.9%; and Dyella, 3.9%), Firmicutes (Bacillus, 42.1%), and Actinobacteria (two isolates showing high identity with the Streptomyces genus, 1.9%) divisions were identified. Fifty percent of the bacterial endophytes produced the phytohormone indole-acetic acid (IAA), eleven of which exhibited higher IAA production (>5.8 mg/mL) compared to the plant growth-promoting strain, Pseudomonas fluorescens UM270. Additionally, the endophytic isolates exhibited protease activity (22%), produced siderophores (26.4%), and demonstrated antagonistic action (>50% inhibition of mycelial growth) against the grey mold phytopathogen Botrytis cinerea (3.9%). These results suggested that field-grown R. fruticosus plants contain bacterial endophytes within their tissues with the potential to promote plant growth and display antagonism towards plant pathogens.
Assuntos
Filogenia , Raízes de Plantas/microbiologia , RNA Ribossômico 16S/genética , Rubus/microbiologia , Actinobacteria/genética , Actinobacteria/isolamento & purificação , Actinobacteria/patogenicidade , Betaproteobacteria/genética , Betaproteobacteria/isolamento & purificação , Betaproteobacteria/patogenicidade , Gammaproteobacteria/genética , Gammaproteobacteria/isolamento & purificação , Gammaproteobacteria/patogenicidade , Raízes de Plantas/genética , Pseudomonas fluorescens/genética , Pseudomonas fluorescens/isolamento & purificação , Pseudomonas fluorescens/patogenicidade , Rubus/genéticaRESUMO
In the present study, we analyzed the frequency of hemolytic and antifungal activities in bacterial isolates from the rhizosphere of Medicago truncatula plants. Of the 2000 bacterial colonies, 96 showed ß-hemolytic activities (frequency, 4.8 x 10(-2)). Hemolytic isolates were analyzed for their genetic diversity by using random amplification of polymorphic DNA, yielding 88 haplotypes. The similarity coefficient of Nei and Li showed a polymorphic diversity ranging from 0.3 to 1. Additionally, 8 of the hemolytic isolates showed antifungal activity toward plant pathogens, Diaporthe phaseolorum, Colletotrichum acutatum, Rhizoctonia solani, and Fusarium oxysporum. The 16S ribosomal sequencing analysis showed that antagonistic bacterial isolates corresponded to Bacillus subtilis (UM15, UM33, UM42, UM49, UM52, and UM91), Bacillus pumilus (UM24), and Bacillus licheniformis (UM88). The present results revealed a higher genetic diversity among hemolytic isolates compared to that of isolates with antifungal action.
Assuntos
Bacillus subtilis/genética , Bacillus/genética , Medicago truncatula/microbiologia , Filogenia , RNA Ribossômico 16S/genética , Microbiologia do Solo , Antibiose , Antifúngicos/metabolismo , Antifúngicos/farmacologia , Bacillus/classificação , Bacillus/metabolismo , Bacillus subtilis/classificação , Bacillus subtilis/metabolismo , Técnicas de Tipagem Bacteriana , Fusarium/efeitos dos fármacos , Fusarium/crescimento & desenvolvimento , Variação Genética , Haplótipos , Hemólise , Técnica de Amplificação ao Acaso de DNA Polimórfico , Rhizoctonia/efeitos dos fármacos , Rhizoctonia/crescimento & desenvolvimento , RizosferaRESUMO
Iron (Fe) is an essential element for plant growth. Commonly, this element is found in an oxidized form in soil, which is poorly available for plants. Therefore, plants have evolved ferric-chelate reductase enzymes (FRO) to reduce iron into a more soluble ferrous form. Fe scarcity in plants induce the FRO enzyme activity. Although the legume Medicago truncatula has been employed as a model for FRO activity studies, only one copy of the M. truncatula MtFRO1 gene has been characterized so far. In this study, we identified multiple gene copies of the MtFRO gene in the genome of M. truncatula by an in silico search, using BLAST analysis in the database of the M. truncatula Genome Sequencing Project and the National Center for Biotechnology Information, and also determined whether they are functional. We identified five genes apart from MtFRO1, which had been already characterized. All of the MtFRO genes exhibited high identity with homologous FRO genes from Lycopersicon esculentum, Citrus junos and Arabidopsis thaliana. The gene copies also presented characteristic conserved FAD and NADPH motifs, transmembrane regions and oxidoreductase signature motifs. We also detected expression in five of the putative MtFRO sequences by semiquantitative RT-PCR analysis, performed with mRNA from root and shoot tissues. Iron scarcity might be a condition for an elevated expression of the MtFRO genes observed in different M. truncatula tissues.
Assuntos
FMN Redutase/genética , Medicago truncatula/enzimologia , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Indução Enzimática , FMN Redutase/metabolismo , Expressão Gênica , Regulação da Expressão Gênica de Plantas , Ferro/metabolismo , Medicago truncatula/genética , Dados de Sequência Molecular , Proteínas de Plantas/metabolismo , Raízes de Plantas/enzimologia , Raízes de Plantas/genética , Brotos de Planta/enzimologia , Brotos de Planta/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência de AminoácidosRESUMO
We looked for bacterial strains with antifungal activity in the sorghum rhizosphere. A prescreening procedure to search for hemolytic activity among the isolated strains allowed us to detect good fungitoxic activity in a bacterial isolate that we named UM96. This bacterial isolate showed strong growth inhibition in bioassays against the pathogens Diaporthe phaseolorum, Colletotrichum acutatum, Rhizoctonia solani, and Fusarium oxysporum. The supernatant of isolate UM96 also showed strong hemolytic activity, which was not observed in the protease-treated supernatant. However, the supernatant that was treated with protease had similar antagonistic effects to those exhibited by the supernatant that was not treated with this enzyme. These results suggest that a bacteriocin-like compound is responsible for the hemolytic activity; whereas, as far as antifungal effect is concerned, an antibiotic of nonribosomal origin, such as a lipopeptide, might be acting. Further molecular characterization by partial 16S rDNA sequencing placed isolate UM96 in a cluster with Bacillus amyloliquefaciens; however, the highest identity match found in databases of Bacillus species was 91% identity. This suggests that Bacillus sp UM96 might be a novel species.
Assuntos
Antifúngicos/farmacologia , Bacillus/genética , Bacillus/isolamento & purificação , Fungos/efeitos dos fármacos , Rizosfera , Sorghum/microbiologia , Sequência de Bases , DNA Ribossômico/genética , Fungos/crescimento & desenvolvimento , Genes Bacterianos/genética , Hemólise/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Dados de Sequência MolecularRESUMO
Gene families are an important and intrinsic trait of rhizobial species. These gene copies can participate in non-reciprocal recombination events, also called gene conversions. Gene conversion has diverse roles, but it is usually implicated in the evolution of multigene families. Here, we searched for gene conversions in multigene families of six representative rhizobial genomes. We identified 11 gene families with different numbers of copies, genome location and function in CFN42 and CIAT652 strains of Rhizobium etli, Rhizobium sp NGR234, Mesorhizobium loti MAFF303099, Sinorhizobium meliloti 1021, and Bradyrhizobium japonicum USDA110. Gene conversions were detected by phylogenetic inference in the nifD and nifK gene families in R. etli. Sequence analysis confirmed multiple gene conversions in these two gene families. We suggest that gene conversion events have an important role in homogenizing multigene families in rhizobia.
Assuntos
Conversão Gênica/genética , Rhizobium/genética , Proteínas de Bactérias/classificação , Proteínas de Bactérias/genética , Bradyrhizobium/genética , Família Multigênica/genética , Filogenia , Sinorhizobium meliloti/genéticaRESUMO
Endophytic bacterial diversity was estimated in Mexican husk tomato plant roots by amplified rDNA restriction analysis and sequence homology comparison of the 16S rDNA genes. Sixteen operational taxonomic units from the 16S rDNA root library were identified based on sequence analysis, including the classes Gammaproteobacteria, Betaproteobacteria, Actinobacteria, and Bacilli. The predominant genera were Stenotrophomonas (21.9%), Microbacterium (17.1%), Burkholderia (14.3%), Bacillus (14.3%), and Pseudomonas (10.5%). In a 16S rDNA gene library of the same plant species' rhizosphere, only common soil bacteria, including Stenotrophomonas, Burkholderia, Bacillus, and Pseudomonas, were detected. We suggest that the endophytic bacterial diversity within the roots of Mexican husk tomato plants is a subset of the rhizosphere bacterial population, dominated by a few genera.
Assuntos
Bactérias/classificação , Raízes de Plantas/microbiologia , Solanum lycopersicum/microbiologia , Bactérias/genética , Sequência de Bases , Primers do DNA , DNA Bacteriano/genética , DNA Ribossômico/genética , Solanum lycopersicum/genética , Raízes de Plantas/genética , Reação em Cadeia da PolimeraseRESUMO
Studies on Rhizobium-legume symbiosis show that trehalose content in nodules under drought stress correlates positively with an increase in plant tolerance to this stress. Fewer reports describe trehalose accumulation in mycorrhiza where, in contrast with rhizobia, there is no flux of carbohydrates from the microsymbiont to the plant. However, the trehalose dynamics in the Mycorrhiza-Rhizobium-Legume tripartite symbiosis is unknown. The present study explores the role of this tripartite symbiosis in the trehalose content of nodules grown under contrasting moisture conditions. Three wild genotypes (P. filiformis, P. acutifolis and P. vulgaris) and two commercial genotypes of Phaseolus vulgaris (Pinto villa and Flor de Mayo) were used. Co-inoculation treatments were conducted with Glomus intraradices and a mixture of seven native rhizobial strains, and trehalose content was determined by GC/MS. The results showed a negative effect of mycorrhizal inoculation on nodule development, as mycorrhized plants showed fewer nodules and lower nodule dry weight compared to plants inoculated only with Rhizobium. Mycorrhizal colonization was also higher in plants inoculated only with Glomus as compared to plants co-inoculated with both microsymbionts. In regard to trehalose, co-inoculation negatively affects its accumulation in the nodules of each genotype tested. However, the correlation analysis showed a significantly positive correlation between mycorrhizal colonization and nodule trehalose content.