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Universidade de São Paulo (2012)

Bactérias associadas às cactáceas da Caatinga : promoção de crescimento de plantas sob estresse hídrico

Nessner Kavamura Vanessa

Titre : Bactérias associadas às cactáceas da Caatinga : promoção de crescimento de plantas sob estresse hídrico

Auteur : Nessner Kavamura Vanessa

Université de soutenance : Universidade de São Paulo

Grade : Doutorado 2012

Caatinga, a Brazilian unique biome, inserted in the semi-arid climate of Brazilian northeast, presents xerophytes with high resistance to drought periods. These plants are found in association with well-adapted microorganisms that have evolved some cellular protection mechanisms against water stress, as well as plant protection against the negative effects of desiccation. This work aimed to study the bacteria associated to some Caatinga cacti, with respect to the structure of bacterial communities of bulk soil and rhizosphere of Cereus jamacaru during the modification of rainy season to dry season, identifying the dominant groups and discussing some functions that enable the soil-cactus-microorganism interaction maintenance during drought. Besides, we searched for drought-tolerant bacteria able to promote plant growth under water stress. Samples were collected along the Caatinga biome in five states : BA, CE, PI, PB, and RN in a total of five points. With unculturable techniques, it was possible to observe that the sampling season (rainy/dry) was the main driver for the modification of bacterial communities’ structure. Proteobacteria and Bacteroidetes phyla were the most abundant during the rainy season while phylum Actinobacteria and Bacillus group were the most abundant during the dry season. With culturable techniques, it was observed a high frequency of strains belonging to genus Bacillus that were able to grow in medium at reduced water activity and displaying some mechanisms of desiccation protection such as the production of exopolysaccharides and biofilm. Furthermore, several strains showed mechanisms of direct and/or indirect plant growth promotion, like the production of fitohormone, availability of P through solubilization, nitrogen fixation, reduction of negative effects caused by stress-induced ethylene, production of cellulase and ammonia. One strain of Bacillus sp. was able to promote maize growth under water stress, increasing some of the analyzed plant parameters. The use of bacterial consortium between two strains, as well as mechanisms displayed by microorganisms under adverse environmental conditions and their functions in plant protection against desiccation are also discussed.

Mots clés : Bacteria ; Bactérias ; Caatinga ; Caatinga ; Cactáceas ; Cacti ; Crescimento vegetal ; Estresse hídrico ; Mandacaru ; Mandacaru ; Plant growth ; Rhizosphere ; Rizosfera ; Semi-arid ; Semiárido ; Water stress


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