RESUMO
This study tested the hypothesis that cocoa monoculture (MS) and cocoa-açai agroforestry systems (AFS) may influence the microbial community structure and populations of plant growth-promoting bacteria (PGPR). Accordingly, the aim was to analyze the microbial community structure and PGPR populations in different agroecosystems in the Brazilian Amazon. To achieve this, the rhizosphere microbial community of cocoa and açai plants in both Amazonian seasons (dry and rainy) was analyzed using culture-dependent (PGPR screening) and -independent methods [PCR-DGGE based on rrs, alp, nifH gene, and intergenic region (ITS) of fungi]. Concerning PGPR screening, out of 48 isolated bacterial strains, 25% were capable of siderophore production, 29% of mineralized organic phosphate, 8% of inorganic phosphate solubilization, and 4% of indole acetic acid production. Moreover, 17% of isolates could inhibit the growth of various phytopathogenic fungi. Statistical analyses of DGGE fingerprints (p < 0.05) showed that bacterial and fungal community structures in the rhizosphere were influenced by the seasons, supporting the results of the physicochemical analysis of the environment. Furthermore, as hypothesized, microbial communities differed statistically when comparing the MS and AFS. These findings provide important insights into the influence of climate and cultivation systems on soil microbial communities to guide the development of sustainable agricultural practices.
RESUMO
Although Tropaeolum majus (nasturtium) is an agriculturally and economically important plant, especially due to the presence of edible flowers and its medicinal properties, its microbiome is quite unexplored. Here, the structure of the total bacterial community associated with the rhizosphere, endosphere and bulk soil of T. majus was determined by 16S rRNA amplicon metagenomic sequencing. A decrease in diversity and richness from bulk soil to the rhizosphere and from the rhizosphere to the endosphere was observed in the alpha diversity analyses. The phylum Proteobacteria was the most dominant in the bacteriome of the three sites evaluated, whereas the genera Pseudomonas and Ralstonia showed a significantly higher relative abundance in the rhizosphere and endosphere communities, respectively. Plant growth-promoting bacteria (236 PGPB) were also isolated from the T. majus endosphere, and 76 strains belonging to 11 different genera, mostly Serratia, Raoultella and Klebsiella, showed positive results for at least four out of six plant growth-promoting tests performed. The selection of PGPB associated with T. majus can result in the development of a biofertilizer with activity against phytopathogens and capable of favoring the development of this important plant.
RESUMO
Resistance to antibiotics is one of the most relevant public health concerns in the world. Aquatic environments play an important role because they are reservoirs for antibiotic resistance genes and antibiotic-resistant strains, contributing to the spread of resistance. The present study investigated the resistome in Lake Bolonha (three sampling sites) in the Amazon region using a metagenomics approach and culture-dependent methods. Whole-metagenome-based results showed that the most abundant phyla were Protobacteria, Actinobacteria, Firmicutes, Bacteroidetes and Cyanobacteria. The composition of the resistome demonstrated that the genes that confer resistance to ß-lactams were prevalent at all sampling sites, followed by genes conferring resistance to aminoglycosides and tetracycline. Acquired genes encoding extended-spectrum ß-lactamases (e.g., bla CTX-M) and resistance to carbapenems (e.g., bla IMP and bla VIM) were detected through metagenome analysis. Bacteria were isolated from culture medium supplemented with cefotaxime or imipenem, and isolates were identified and analyzed for their antibiotic susceptibility profiles and resistance genes. In total, 98 bacterial isolates belonging to the genera Pseudomonas (37), Acinetobacter (32), Klebsiella (13), Enterobacter (9), Pantoe (3), Stenotrophomonas (3), and Methylobacterium (1) were obtained. Among isolates, the most abundant genes were bla CTX-M (28.3%), bla SHV (22.6%) and bla TEM (18.8%) in isolates from cefotaxime-supplemented medium and bla VIM (28.8%) and bla IMP (22.2%) in isolates recovered from imipenem-supplemented medium. The genes intl1 and intl2 were detected in 19.3% and 7.1% of isolates. Antibiograms showed that 94.9% (from cefotaxime-supplemented medium) and 85.7% (from imipenem-supplemented medium) of the isolates were multidrug resistant. Besides cefotaxime and imipenem, isolates were mostly resistant to aztreonam (91.8%), amoxicillin (98.8%), ampicillin (82.6%), and nalidixic acid (77.5%). Hence, the present study demonstrates that Lake Bolonha is a reservoir of bacteria resistant to antibiotics and resistance genes, some of which are of critical importance to human health.
RESUMO
Sweet potato is a subsistence crop cultivated worldwide. Although it is generally considered tolerant to different diseases, it is quite susceptible to the fungus Plenodomus destruens that causes foot-rot disease. Plant growth-promoting bacteria associated with sweet potato remain poorly studied, but some Bacillus strains may have potential as biological control agents. Here, we evaluate the persistence of two bacterial strains-Bacillus safensis T052-76 and Bacillus velezensis T149-19-in pot experiments and assess their impact on indigenous bacterial and fungal communities associated with sweet potato. Numbers of cells of both strains introduced into pots remained stable in the rhizosphere of sweet potato over the 180-day experiment. Denaturing gradient gel electrophoresis based on the rrs gene encoding bacterial 16S rRNA and the fungal ribosomal internal transcribed spacer region showed that bands corresponding to the introduced strains were not detected in plant endosphere. PERMANOVA and non-metric multidimensional scaling statistical analyses showed that: (1) strain T052-76 altered the structure of the indigenous bacterial community (rhizosphere and soil) more than strain T149-19; (2) T052-76 slightly altered the structure of the indigenous fungal community (rhizosphere and soil) and (3) strain T149-19 did not disturb the fungal community. Our results demonstrate the stability of both Bacillus strains in the sweet potato rhizosphere and, apart from the influence of B. safensis T052-76 on the bacterial community, their limited impact on the microbial community associated with this important crop plant.