Bacterial activity in heavy metals polluted soils: Metal efflux systems in native rhizobial strains

The negative effect of high levels of heavy metals on the activity of soil microorganisms is well-known. However, some microorganisms survive even in high levels of heavy metals, and the microbial activity can therefore, help to recover these polluted soils. Microbial metal uptake in contaminated soils has to be tightly regulated to avoid toxic effects for the cells. These mechanisms of metal resistance are frequently associated to transport-related membrane proteins that mediate bacterium’s direct metabolic interactions with the complex soil and aquatic harsh environments. This study reports the identification of gene clusters in rhizobial strains that are regulated by heavy metals, particularly chromium. A DNA fragment was amplified from R. leguminosarum, and in silico analysis of the sequence obtained revealed a putative protein homologue to a cation/multidrug efflux pump component (GenBank DQ398937). Another amplified DNA fragment, with 960 bp, has strong homology with anion ABC transporters (GenBank ZP 002212691) and a peptide ABC transporter (Gen- Bank NP 766950), was identified in Mesorhizobium loti (GenBank DQ398941) and Sinorhizobium meliloti. Using ChromosomeWalking technique, a single product from Sinorhizobium meliloti was cloned and sequenced. This new fragment enlarged more 302 bp to the initial sequence corresponding to the ABC transporter, confirming homology with an ATPase from PP superfamily (GenBank ZP 00197146.1)

Applications of Essential Oils as Antibacterial Agents in Minimally Processed Fruits and Vegetables - A Review

Microbial foodborne diseases are a major health concern. In this regard, one of the major risk factors is related to consumer preferences for “ready-to-eat” or minimally processed (MP) fruits and vegetables. Essential oil (EO) is a viable alternative used to reduce pathogenic bacteria and increase the shelf-life of MP foods, due to the health risks associated with food chlorine. Indeed, there has been increased interest in using EO in fresh produce. However, more information about EO applications in MP foods is necessary. For instance, although in vitro tests have defined EO as a valuable antimicrobial agent, its practical use in MP foods can be hampered by unrealistic concentrations, as most studies focus on growth reductions instead of bactericidal activity, which, in the case of MP foods, is of utmost importance. The present review focuses on the effects of EO in MP food pathogens, including the more realistic applications. Overall, due to this type of information, EO could be better regarded as an added value to the food industryinfo:eu-repo/semantics/publishedVersio

potential for soil health improvement anwd plant growth promotion

Funding text: This work was supported by funds from Camões, Instituto da Cooperação e da Língua and Fundação para a Ciência e a Tecnologia through the research unit UIDB/00239/2020 (CEF), the PhD grant SFRH/BD/113951/2015 (Ivete Sandra Maquia), and the contribution to the International Rice Research Institute.(1) Aims: Assessing bacterial diversity and plant-growth-promoting functions in the rhizosphere of the native African trees Colophospermum mopane and Combretum apiculatum in three landscapes of the Limpopo National Park (Mozambique), subjected to two fire regimes. (2) Methods: Bacterial communities were identified through Illumina Miseq sequencing of the 16S rRNA gene amplicons, followed by culture dependent methods to isolate plant growth-promoting bacteria (PGPB). Plant growth-promoting traits of the cultivable bacterial fraction were further analyzed. To screen for the presence of nitrogen-fixing bacteria, the promiscuous tropical legume Vigna unguiculata was used as a trap host. The taxonomy of all purified isolates was genetically verified by 16S rRNA gene Sanger sequencing. (3) Results: Bacterial community results indicated that fire did not drive major changes in bacterial abundance. However, culture-dependent methods allowed the differentiation of bacterial communities between the sampled sites, which were particularly enriched in Proteobacteria with a wide range of plant-beneficial traits, such as plant protection, plant nutrition, and plant growth. Bradyrhizobium was the most frequent symbiotic bacteria trapped in cowpea nodules coexisting with other endophytic bacteria. (4) Conclusion: Although the global analysis did not show significant differences between landscapes or sites with different fire regimes, probably due to the fast recovery of bacterial communities, the isolation of PGPB suggests that the rhizosphere bacteria are driven by the plant species, soil type, and fire regime, and are potentially associated with a wide range of agricultural, environmental, and industrial applications. Thus, the rhizosphere of African savannah ecosystems seems to be an untapped source of bacterial species and strains that should be further exploited for bio-based solutions.publishersversionpublishe

The Rhizobia-Lotus Symbioses: Deeply Specific and Widely Diverse

The symbiosis between Lotus and rhizobia has been long considered very specific and only two bacterial species were recognized as the microsymbionts of Lotus: Mesorhizobium loti was considered the typical rhizobia for the L. corniculatus complex, whereas Bradyrhizobium sp. (Lotus) was the symbiont for L. uliginosus and related species. As discussed in this review, this situation has dramatically changed during the last 15 years, with the characterization of nodule bacteria from worldwide geographical locations and from previously unexplored Lotus spp. Current data support that the Lotus rhizobia are dispersed amongst nearly 20 species in five genera (Mesorhizobium, Bradyrhizobium, Rhizobium, Ensifer, and Aminobacter). As a consequence, M. loti could be regarded an infrequent symbiont of Lotus, and several plant–bacteria compatibility groups can be envisaged. Despite the great progress achieved with the model L. japonicus in understanding the establishment and functionality of the symbiosis, the genetic and biochemical bases governing the stringent host-bacteria compatibility pairships within the genus Lotus await to be uncovered. Several Lotus spp. are grown for forage, and inoculation with rhizobia is a common practice in various countries. However, the great diversity of the Lotus rhizobia is likely squandered, as only few bacterial strains are used as inoculants for Lotus pastures in very different geographical locations, with a great variety of edaphic and climatic conditions. The agroecological potential of the genus Lotus can not be fully harnessed without acknowledging the great diversity of rhizobia-Lotus interactions, along with a better understanding of the specific plant and bacterial requirements for optimal symbiotic nitrogen fixation under increasingly constrained environmental conditions

Efeito da contaminacao por metais pesados na simbiose rhizobium-leguminosa

Effects of heavy metals on symbiotic nitrogen fixation were studied, suing a soil from an industrial area polluted for nearly 40 years. To evaluate effectiveness and genetic diversity of the rhizobial population, trifolium subterraneum, L. and Trifolium repens, L., were used as trap hosts. The results showed a decrease in effectiveness, determined by acetylene reduction assay, of Rhizobium leguminosarum b v. trifolii isolates obtained from both clovers grown in contaminated soil. Diversity of rhizobial population, analysed by plasmid profiles, showed also a decrease in contaminated soil. The behaviour of Rhizobium isolates introduced into contaminated soil were studied. Seven isolates were selected, two from contaminated soil and five from uncontaminated soil, and survival, plasmid stability and nitrogenase activity were measured. Differences in Rhizobium survival were only detected after 12 months. The isolates from contaminated soil survived better and also two from uncontaminated soil, albeit with changes in their plasmid profiles. Plasmid profiles of the remaining isolates were stable and similar to the original isolates. Nitrogenase activity was similar during all the experiments and the isolates from uncontaminated soil had lower effectiveness than the original. To study tolerance to Cu, Zn and Hg, five Rhizobium isolates were used. The tolerance levels of three isolates with altered plasmid profiles were similar to the isolate from contaminated soil but higher than the tolerance of the original isolate used as the controlAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Diversity, Phylogeny and Plant Growth Promotion Traits of Nodule Associated Bacteria Isolated from Lotus parviflorus

© 2020 by the authors.Lotus spp. are widely used as a forage to improve pastures, and inoculation with elite rhizobial strains is a common practice in many countries. However, only a few Lotus species have been studied in the context of plant-rhizobia interactions. In this study, forty highly diverse bacterial strains were isolated from root nodules of wild Lotus parviflorus plants growing in two field locations in Portugal. However, only 10% of these isolates could nodulate one or more legume hosts tested, whereas 90% were thought to be opportunistic nodule associated bacteria. Phylogenetic studies place the nodulating isolates within the Bradyrhizobium genus, which is closely related to B. canariense and other Bradyrhizobium sp. strains isolated from genistoid legumes and Ornithopus spp. Symbiotic nodC and nifH gene phylogenies were fully consistent with the taxonomic assignment and host range. The non-nodulating bacteria isolated were alpha- (Rhizobium/Agrobacterium), beta- (Massilia) and gamma-proteobacteria (Pseudomonas, Lysobacter, Luteibacter, Stenotrophomonas and Rahnella), as well as some bacteroidetes from genera Sphingobacterium and Mucilaginibacter. Some of these nodule-associated bacteria expressed plant growth promotion (PGP) traits, such as production of lytic enzymes, antagonistic activity against phytopathogens, phosphate solubilization, or siderophore production. This argues for a potential beneficial role of these L. parviflorus nodule-associated bacteria.Financial support was given by the projects PRODER, PA 54970 and ALT20-45-2015-08.Peer reviewe

Antagonistic compounds from controversial bacteria with suppressing effects on the diseases caused by Phytophthora cinnamomi

This work focuses on the importance of considering the bio-substances evaluation of controversial strains against plant pathogens. The bacterial population of plant rhizosphere covers every type of plant–microbe interaction. Some of them have beneficial effects on plant growth and showed antagonistic activities against plant pathogens. The distribution of the Burkholderia genus is wide in soils, and many bacterial strains were proven to benefit and protect important crops from pathogen threats. In this study, it was possible to obtain a Burkholderia cenocepacia isolate from the rhizosphere soil of a leguminous plant. It was screened in vitro for its abilities to protect Trifolium subterraneum L. from Phytophthora cinnamomi. The current results revealed that plants enhanced the growth in plants inoculated with both, the bacterial strain and the pathogen probably because the bacteria produced antagonistic compounds such as hydrolytic enzymes. This report shows the potential ability of a rhizobacterium naturally existing in the soils to suppress the effects of the diseases caused by P. cinnamomi.Fil: Colavolpe, Maria Belen. Instituto Nacional de Investigação Agrária e Veterinária; Portugal. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Silva, Márcia de Castro. Instituto Nacional de Investigação Agrária e Veterinária; PortugalFil: Maguire, Vanina Giselle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Costa, Augusta. Universidade Nova de Lisboa; Portugal. Instituto Nacional de Investigação Agrária e Veterinária; PortugalFil: Videira e Castro, Isabel. Instituto Nacional de Investigação Agrária e Veterinária; PortugalFil: Ruiz, Oscar Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); Argentin

Número 12

Beitrag präsentiert im Rahmen der Veranstaltung "Bildungsräume – Bildungsorte. Historische Perspektiven", 29. Oktober 2015, Pädagogische Hochschule Zürich