RESUMO
Compared to agrochemicals, bioinoculants based on plant microbiomes are a sustainable option for increasing crop yields and soil fertility. From the Mexican maize landrace "Raza cónico" (red and blue varieties), we identified yeasts and evaluated in vitro their ability to promote plant growth. Auxin production was detected from yeast isolates and confirmed using Arabidopsis thaliana plants. Inoculation tests were performed on maize, and morphological parameters were measured. Eighty-seven yeast strains were obtained (50 from blue corn and 37 from red corn). These were associated with three families of Ascomycota (Dothideaceae, Debaryomycetaceae, and Metschnikowiaceae) and five families of Basidiomycota (Sporidiobolaceae, Filobasidiaceae, Piskurozymaceae, Tremellaceae, and Rhynchogastremataceae), and, in turn, distributed in 10 genera (Clavispora, Rhodotorula, Papiliotrema, Candida, Suhomyces, Soliccocozyma, Saitozyma Holtermaniella, Naganishia, and Aeurobasidium). We identified strains that solubilized phosphate and produced siderophores, proteases, pectinases, and cellulases but did not produce amylases. Solicoccozyma sp. RY31, C. lusitaniae Y11, R. glutinis Y23, and Naganishia sp. Y52 produced auxins from L-Trp (11.9-52 µg/mL) and root exudates (1.3-22.5 µg/mL). Furthermore, they stimulated the root development of A. thaliana. Inoculation of auxin-producing yeasts caused a 1.5-fold increase in maize plant height, fresh weight, and root length compared to uninoculated controls. Overall, maize landraces harbor plant growth-promoting yeasts and have the potential for use as agricultural biofertilizers.
RESUMO
Environmental pollution as a result of heavy metals (HMs) is a worldwide problem and the implementation of eco-friendly remediation technologies is thus required. Metallophores, low molecular weight compounds, could have important biotechnological applications in the fields of agriculture, medicine, and bioremediation. This study aimed to isolate HM-resistant bacteria from soils and sediments of the Lerma-Chapala Basin and evaluated their abilities to produce metallophores and to promote plant growth. Bacteria from the Lerma-Chapala Basin produced metallophores for all the tested metal ions, presented a greater production of As3+ metallophores, and showed high HM resistance especially to Zn2+, As5+, and Ni2+. A total of 320 bacteria were isolated with 170 strains showing siderophores synthesis. Members of the Delftia and Pseudomonas genera showed above 92 percent siderophore units (psu) during siderophores production and hydroxamate proved to be the most common functional group among the analyzed siderophores. Our results provided evidence that Lerma-Chapala Basin bacteria and their metallophores could potentially be employed in bioremediation processes or may even have potential for applications in other biotechnological fields.
Assuntos
Metais Pesados , Poluentes do Solo , Bactérias/genética , Biodegradação Ambiental , Metais Pesados/análise , Solo , Poluentes do Solo/análiseRESUMO
Mexican maize landraces, produced for local consumption, are adapted to different environmental conditions, and their yield is affected by abiotic and biotic factors, including the use of agrochemicals. The search for sustainable alternatives to agrochemicals includes the study of the culturable microbial communities. In this study, the fungal communities associated with 2 Mexican maize landraces reddish and bluish "conical cobs" were found to be comprised of Ascomycota fungi, represented by 89 strains within 6 orders (Pleosporales, Hypocreales, Onygenales, Capnodiales, Helotiales, and Eurotiales) and 16 genera. Cellulases and metallophores production were the primary enzymatic products and plant growth-promoting activities were detected among the isolates. Penicillium, Didymella, and Fusarium strains had the most active enzymatic and plant growth promoting activities, however, Aspergillus sp. HES2-2.2, Talaromyces sp. RS1-7, and Penicillium sp. HFS3-3 showed antagonistic activity against the four phytopathogenic Fusarium strains Fusarium oxysporum, Fusarium sambucinum, Fusarium fujikuroi and Fusarium incarnatum-equiseti and also a high and diverse production of enzymatic and plant growth promoting activities; here we identified fungal strains as candidates to promote maize growth.
Assuntos
Ascomicetos , Fusarium , Microbiota , Penicillium , Aspergillus , Fungos , Zea maysRESUMO
Arsenic contamination is an important environmental problem around the world since its high toxicity, and bacteria resist to this element serve as valuable resource for its bioremediation. Aiming at searching the arsenic-resistant bacteria and determining their resistant mechanism, a total of 27 strains isolated from roots of Prosopis laevigata and Spharealcea angustifolia grown in a heavy metal-contaminated region in Mexico were investigated. The minimum inhibitory concentration (MIC) and transformation abilities of arsenate (As5+) and arsenite (As3+), arsenophore synthesis, arsenate uptake, and cytoplasmatic arsenate reductase (arsC), and arsenite transporter (arsB) genes were studied for these strains. Based on these results and the 16S rDNA sequence analysis, these isolates were identified as arsenic-resistant endophytic bacteria (AREB) belonging to the genera Arthrobacter, Bacillus, Brevibacterium, Kocuria, Microbacterium, Micrococcus, Pseudomonas, and Staphylococcus. They could tolerate high concentrations of arsenic with MIC from 20 to > 100 mM for As5+ and 10-20 mM for As3+. Eleven isolates presented dual abilities of As5+ reduction and As3+ oxidation. As the most effective strains, Micrococcus luteus NE2E1 reduced 94% of the As5+ and Pseudomonas zhaodongensis NM2E7 oxidized 46% of As3+ under aerobic condition. About 70 and 44% of the test strains produced arsenophores to chelate As5+ and As3+, respectively. The AREB may absorb arsenate via the same receptor of phosphate uptake or via other way in some case. The cytoplasmic arsenate reductase and alternative arsenate reduction pathways exist in these AREB. Therefore, these AREB could be candidates for the bioremediation process.
Assuntos
Arsênio/metabolismo , Bactérias/isolamento & purificação , Endófitos/metabolismo , Magnoliopsida/microbiologia , Prosopis/microbiologia , Arseniatos/metabolismo , Arsenitos/metabolismo , Bactérias/classificação , Bactérias/genética , Bactérias/metabolismo , Biodegradação Ambiental , DNA Ribossômico/genética , Endófitos/classificação , Endófitos/genética , Endófitos/isolamento & purificação , Magnoliopsida/metabolismo , México , Mineração , Filogenia , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , RNA Ribossômico 16S/genéticaRESUMO
To evaluate the interactions among endophytes, plants and heavy metal/arsenic contamination, root endophytic bacteria of Prosopis laevigata (Humb and Bonpl. ex Willd) and Sphaeralcea angustifolia grown in a heavy metal(loid)-contaminated zone in San Luis Potosi, Mexico, were isolated and characterized. Greater abundance and species richness were found in Prosopis than in Sphaeralcea and in the nutrient Pb-Zn-rich hill than in the poor nutrient and As-Cu-rich mine tailing. The 25 species identified among the 60 isolates formed three groups in the correspondence analysis, relating to Prosopis/hill (11 species), Prosopis/mine tailing (4 species) and Sphaeralcea/hill (4 species), with six species ungrouped. Most of the isolates showed high or extremely high resistance to arsenic, such as ≥100 mM for As(V) and ≥20 mM for As(III), in mineral medium. These results demonstrated that the abundance and community composition of root endophytic bacteria were strongly affected by the concentration and type of the heavy metals and metalloids (arsenic), as well as the plant species.
Assuntos
Bactérias/metabolismo , Endófitos/isolamento & purificação , Fabaceae/microbiologia , Malvaceae/microbiologia , Metais Pesados/metabolismo , Prosopis/microbiologia , Bactérias/isolamento & purificação , Endófitos/metabolismo , México , Mineração , Filogenia , Raízes de Plantas/microbiologia , Solo/químicaRESUMO
Yeasts were quantified and isolated from the rhizospheres of 5 plant species grown at 2 sites of a Mexican region contaminated with arsenic, lead, and other heavy metals. Yeast abundance was about 10(2) CFU/g of soil and 31 isolates were obtained. On the basis of the phylogenetic analysis of 26S rRNA and internal transcribed spacer fragment, 6 species were identified within the following 5 genera: Cryptococcus (80.64%), Rhodotorula (6.45%), Exophiala (6.45%), Trichosporon (3.22%), and Cystobasidium (3.22%). Cryptococcus spp. was the predominant group. Pectinases (51.6%), proteases (51.6%), and xylanases (41.9%) were the enzymes most common, while poor production of siderophores (16.1%) and indole acetic acid (9.67%) was detected. Isolates of Rhodotorula mucilaginosa and Cystobasidium sloffiae could promote plant growth and seed germination in a bioassay using Brassica juncea. Resistance of isolates by arsenic and heavy metals was as follows: As(3+) ≥ 100 mmol/L, As(5+) ≥ 30 mmol/L, Zn(2+) ≥ 2 mmol/L, Pb(2+) ≥ 1.2 mmol/L, and Cu(2+) ≥ 0.5 mmol/L. Strains of Cryptococcus albidus were able to reduce arsenate (As(5+)) into arsenite (As(3+)), but no isolate was capable of oxidizing As(3+). This is the first study on the abundance and identification of rhizosphere yeasts in a heavy-metal- and arsenic-contaminated soil, and of the reduction of arsenate by the species C. albidus.