Banca de DEFESA: FRANCISCO MATHEUS MEDEIROS DE FREITAS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : FRANCISCO MATHEUS MEDEIROS DE FREITAS
DATE: 25/02/2026
TIME: 13:00
LOCAL: online
TITLE:

Functional Diversity of the Genus Nitrospirillum: Characterization of Mechanisms Associated with Plant Growth Promotion

KEY WORDS:

Functional genomics. Growth promotion. Diazotrophic bacteria. Plant-Bacteria

PAGES: 140
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Microbiologia e Bioquímica do Solo
SUMMARY:

Food security and the sustainability of tropical agricultural systems demand strategies that reduce dependence on synthetic inputs and increase nutrient use efficiency. In this context, plant growth-promoting bacteria (PGPB) represent a promising alternative, although many genera with agronomic potential remain underexplored. The genus Nitrospirillum, known for its capacity for biological nitrogen fixation in grasses, lacks integrated studies linking its genomic diversity to the functional mechanisms of growth promotion. This dissertation aimed to characterize the functional diversity of type strains of Nitrospirillum spp., integrating in silico genomic analyses, in vitro biochemical assays, and in vivo physiological evaluations in maize and brachiaria. In Chapter I, ten strains were analyzed for the presence of genes and metabolic pathways associated with growth promotion mechanisms, as well as their phenotypic expressions. The results revealed that Nitrospirillum does not use the canonical tryptophan-dependent routes for the synthesis of indole-3-acetic acid (IAA), but employs an alternative pathway mediated by the enzyme amidase (EC 3.5.1.4), favoring the production of phenylacetic acid (PAA), a non-indolic auxin. All strains showed the ability to solubilize phosphorus from tricalcium phosphate, associated with the presence of pathways for the production of organic acids such as citrate and malate, but were inactive against iron and aluminum phosphates. Zinc solubilization was more efficient for zinc oxide (ZnO) than for zinc phosphate (Zn₃(PO₄)₂). Siderophore production and biofilm formation varied significantly among strains, correlating with the completeness of amino acid and polyamine biosynthesis pathways, respectively. The ACC-deaminase enzyme was absent in all strains, indicating a distinct metabolic specialization. In Chapter II, the strains were evaluated for growth promotion in maize (Zea mays L.) and brachiaria (Urochloa brizantha) plants. Inoculation with strain BR 11140 promoted significant increases in height (19%), leaf area (123%), and shoot biomass (39%) of the maize cultivar SHS 5050 compared to the non-inoculated control. The response to inoculation was dependent on plant genotype, with the cultivar AG 8088 PRO2 showing lower responsiveness. In brachiaria, under low nitrogen availability (0.6 mM), some strains maintained the capacity to promote growth, suggesting potential for use under nutrient-restricted conditions. It is concluded that the genus Nitrospirillum possesses a unique metabolic architecture, based on the production of alternative auxins (PAA) and selective nutrient solubilization, with strains that demonstrate effective growth promotion capacity in grasses of agronomic interest. Inoculation efficiency is modulated by strain-cultivar specificity and nitrogen availability, reinforcing the need for precise selection of combinations for the development of inoculants adapted to sustainable agricultural systems.

COMMITTEE MEMBERS:
Presidente - ***.881.579-** - JERRI ÉDSON ZILLI - EMBRAPA
Interno - 2626406 - LEANDRO AZEVEDO SANTOS
Interna - ***.052.847-** - VERONICA MASSENA REIS - EMBRAPA
Externo à Instituição - GABRIELA CAVALCANTI ALVES