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Caracterização de rizobactérias no porta-enxerto citrumelo ‘swingle’ sob sistemas de cultivos orgânico e convencional
(Universidade Federal de São Carlos, 2025-05-22) Mancine, Nathália; Lima, Helena Santiago; https://lattes.cnpq.br/8307191971212434; Coletta-Filho, Helvécio Della; https://lattes.cnpq.br/8783964270386788; https://lattes.cnpq.br/9948565341546913
Understanding the impact of the plant microbiome has driven new strategies to enhance agricultural production, especially in the face of climate change, increased prevalence of pathogens, and adverse growing conditions. Studying soil microorganisms is essential for transforming the rhizosphere to benefit plants, but there is still a knowledge gap regarding the prospecting of Plant Growth-Promoting Bacteria (PGPB) in citrus, particularly when comparing different cultivation systems. This project investigated citrus rhizobacteria under organic and conventional cultivation systems, aiming to identify microorganisms with potential for the formulation of synthetic communities (SynComs) and their application as bioinputs. Rhizospheric soil samples were collected for total soil DNA sequencing to perform metataxonomic analyses, and root samples were collected to isolate bacterial populations from the rhizosphere and rhizoplane using four culture media to maximize bacterial diversity. After morphological selection, the isolates were cryopreserved and taxonomically characterized by sequencing the V4-V5 region of the 16S rRNA gene using the Illumina platform (250x250bp paired-end), allowing identification at the genus level. Through in silico analyses, a core community of approximately 76% was observed across both cultivation systems, along with higher alpha diversity and a greater number of biomarkers in organic cultivation. Beta diversity indicated that the cultivation type explained 25% of the variation in microbial community composition. In vitro assays were conducted to functionally characterize the isolates, including phosphate solubilization, indole-3-acetic acid (IAA) production, siderophore production, and nitrogen fixation tests. In vivo assays were also carried out, including seed germination tests and seed inoculation in seedling trays under greenhouse conditions to assess the potential of the bacteria as PGPB. A total of 61 isolates were tested in vitro, with up to 70% of isolates from organically grown plants exhibiting phosphate solubilization ability and approximately 80% demonstrating siderophore production potential. In contrast, isolates from conventional cultivation stood out for their biological nitrogen fixation capacity, with 55% showing this trait. In the seed germination tests, isolates from the organic system significantly accelerated germination speed and vigor, while the SynCom formed from conventionally derived bacteria—selected based on their growth-promotion abilities—showed a significant positive effect (p<0.05) on root mass (g). In the in vivo assays, 16 isolates significantly increased (p<0.05) root volume in plants. The results of this study reinforce the potential of the isolated bacteria, particularly from organic cultivation, in promoting plant growth and developing sustainable strategies for citrus farming. Furthermore, the formation of SynComs represents an innovative approach for the formulation of bioinputs, contributing to plant resilience under different cultivation conditions.
Avaliação do efeito combinado de tratamento superficial à laser e passivação no limite de fadiga em flexão da liga comercial Ti-6Al-4V ELI
(Universidade Federal de São Carlos, 2025-05-22) Silva Wolf, Eduardo Henrique; Camilo Magalhães, Danielle Cristina; https://lattes.cnpq.br/5486724956564584; https://orcid.org/0000-0001-5857-4902; Rovere, Carlos Alberto Della; https://lattes.cnpq.br/8141224513975606; https://orcid.org/0000-0003-1534-0561; https://lattes.cnpq.br/9143097364274410; https://orcid.org/0000-0001-7894-9732
Laser irradiation is a widely used technology for the surface modification of titanium alloy implants, enabling their identification and traceability. This process locally heats the alloy surface, generating a dark oxide layer. Subsequent passivation with nitric acid is commonly applied to reduce reactivity and enhance corrosion resistance. However, the combination of these treatments represents a significant challenge in the industry due to the variety of parameters affecting surface topography and microstructure. In this context, the objective of this project was to evaluate the combined effect of a surface treatment using Nd:YAG laser irradiation and nitric acid passivation on the fatigue limit of Ti-6Al-4V ELI alloy. The four-point bending fatigue tests was employed, applying the fatigue limit value at 1 million cycles defined according to ASTM F382:17 standard. Scanning electron microscopy (SEM) was used to characterize the irradiated and fractured surfaces to establish a correlation between surface modification and fatigue limit. The results showed that the fatigue limit of 615 MPa for the polished and passivated condition was maintained compared to the polished condition. After irradiation, a 58,5% reduction in the fatigue limit was observed, reaching 255 MPa. Finally, passivation after irradiation resulted in a 47,1% increase compared to the irradiated condition, reaching 375 MPa. The increase in fatigue limit from 255 to 375 MPa after passivation can be attributed to the reduction in surface roughness (Ra and Rz), reducing stress concentration and delaying crack propagation. The significance of these results lies in the optimization of surface treatments for titanium implants, aiming to improve their durability and performance in biomedical applications.