Background: Conventional agriculture relies on chemical pesticides and fertilizers, which can degrade ecosystems. A reduction of these harmful practices is required, replacing (or integrating) them with more eco-friendly approaches, such as microbial inoculation. Tomato is an important agricultural product, with a high content of bioactive compounds (folate, ascorbate, polyphenols, and carotenoids). The focus of this research was to investigate the plant growth-promoting (PGP) abilities of bacterial strains isolated from different tomato cultivars, with the aim to develop systems to improve plant health and crop productivity based on microbial inoculation. Methods:A pool of different tomato cultivars already available on the market and new tomato hybrids were selected based on their nutritional quality (high content of biologically active compounds). A total of 23 strains were isolated from tomato roots (11 rhizospheric strains and 12 root endophytes). The cultivable isolates were analyzed for a number of different PGP traits: organic acids (OA), indole acetic acid (IAA), ACC deaminase, and siderophore production. The effects of microbial inoculation on root growth of Arabidopsis thaliana were also evaluated using a Vertical Agar Plate assay. Results:A high percentage of the isolated strains tested positive for the following PGP traits: 73 % were able to produce OA, 89 % IAA, 83 % ACC deaminase, and 87 % siderophores. The most striking result were remarkable increases in the formation of root hairs for most of the inoculated plants. This effect was obvious for all A. thaliana seedlings inoculated with the isolated endophytes, and for the 50 % of the seedlings inoculated with the rhizospheric strains.

Recovery of arsenic contaminated areas is a challenge society faces throughout the world. Revegetation associated with microbial activity can play an essential role in this process. This work investigated biological attributes in a gold mining area with different arsenic contents at different sites under two types of extant revegetation associated with cover layers of the soil: BS, Brachiaria sp. and Stizolobium sp., and LEGS, Acacia crassicarpa, A. holosericea, A. mangium, Sesbania virgata, Albizia lebbeck and Pseudosamanea guachapele. References were also evaluated, comprising the following three sites: B1, weathered sulfide substrate without revegetation; BM, barren material after gold extraction and PRNH (private reserve of natural heritage), an uncontaminated forest site near the mining area. The organic and microbial biomass carbon contents and substrate-induced respiration rates for these sites from highest to lowest were: PRNH > LEGS > BS > B1 and BM. These attributes were negatively correlated with soluble and total arsenic concentration in the soil. The sites that have undergone revegetation (LEGS and BS) had higher densities of bacteria, fungi, phosphate solubilizers and ammonium oxidizers than the sites without vegetation. Principal component analysis showed that the LEGS site grouped with PRNH, indicating that the use of leguminous species associated with an uncontaminated soil cover layer contributed to the improvement of the biological attributes. With the exception of acid phosphatase, all the biological attributes were indicators of soil recovery, particularly the following: microbial carbon, substrate-induced respiration, density of culturable bacteria, fungi and actinobacteria, phosphate solubilizers and metabolic quotient.

Arbuscular mycorrhizal fungi (AMF) improve the tolerance of hosting plants to arsenic (As) in contaminated soils. This work assessed the phytoprotective effect of Glomus etunicatum, Acaulospora morrowiae, Gigaspora gigantea, and Acaulospora sp. on four leguminous species (Acacia mangium, Crotalaria juncea, Enterolobium contortisiliquum, and Stizolobium aterrimum) in an As-contaminated soil from a gold mining area. AMF root colonization, biomass production, As and P accumulation, as well as arsenic translocation index (TI) from roots to shoots were measured. The AMF phytoprotective effect was assessed by the P/As ratio and the activity of plant antioxidant enzymes. The AMF colonization ranged from 24 to 28%. In general, all leguminous species had low As TI when inoculated with AMF species. Inoculation of C. juncea with Acaulospora sp. improved significantly As accumulation in roots, and decreased the activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), highlighting its phytoprotective effect and the potential use of this symbiosis for phytoremediation of As-contaminated soils. However, S. aterrimum has also shown a potential for phytoremediation irrespectively of AMF inoculation. APX was a good indicator of the phytoprotective effect against As contamination in C. juncea and A. mangium. In general P/As ratio in shoots was the best indicator of the phytoprotective effect of all AMF species in all plant species.

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Efficient N-fixing Leguminosae nodulating bacteria resistant to As may facilitate plant growth on As-contaminated sites. In order to identify bacteria holding these features, 24 strains were isolated from nodules of the trap species Crotalaria spectabilis (12) and Stizolobium aterrimum (12) growing on an As-contaminated gold mine site. 16S rRNA gene sequencing revealed that most of the strains belonged to the group of α-Proteobacteria, being representatives of the genera Bradyrhizobium, Rhizobium, Inquilinus, Labrys, Bosea, Starkeya, and Methylobacterium. Strains of the first four genera showed symbiotic efficiency with their original host, and demonstrated in vitro specific plant-growth-promoting (PGP) traits (production of organic acids, indole-3-acetic-acid and siderophores, 1-aminocyclopropane-1-carboxylate deaminase activity, and Ca(PO) solubilization), and increased resistance to As, Zn, and Cd. In addition, these strains and some type and reference rhizobia strains exhibited a wide resistance spectrum to β-lactam antibiotics. Both intrinsic PGP abilities and multi-element resistance of rhizobia are promising for exploiting the symbiosis with different legume plants on trace-element-contaminated soils.

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Resumo Este estudo engloba o tratamento florístico de Apodanthaceae para as cangas da Serra dos Carajás, no estado do Pará. Inclui descrição, ilustração, fotografias, distribuição, comentários morfológicos e taxonômicos de Pilostyles blanchetii, a única espécie da família registrada na área de estudo.