Isolamento e caracterização de bactérias associadas a rizosfera de plantas halófitas

Abstract

Most plant species, especially crops, do not tolerate high salt concentrations. However, halophytic plants are adapted to saline soils. In the rhizosphere of these plants, associations with microorganisms can promote plant growth and increase resistance to salt stress. Therefore, this work aimed to isolate and identify bacteria from the rhizosphere of halophyte plants from different saline environments in the state of Rio de Janeiro and to evaluate their capacity to promote growth of rice. Samples of rhizospheric soils from halophytic plants Salicornia gaudicahudiana, Salicornia fruticosa, Blutaparon portulacoides, Sporobolus virginucus, and Cyperus ligularis were collected. Culture media amended with 1%, 5%, 15%, 20%, and 25% of NaCl were used for bacterial isolation. The bacterial strains were classified according to growth at different NaCl concentrations and were identified by Matrix Assisted Laser Desorption Ionization Time Of Flight/ Mass Spectrometry (MALDI-TOF MS) and by rrs gene sequencing. Subsequently, the potential of nine strains of halotolerant bacteria belonging to the genus Pseudomonas and Bacillus in promoting rice growth at concentrations of 50 mM and 200 mM was analyzed. Thus, germination percentage, total root length, root volume, root surface area, number of tips, and total shoot length were analyzed. A total of 315 bacteria classified as non-halophilic (99/315), halotolerant (171/315) and moderately halophilic (32/315) were isolated. Of the isolated bacteria, 286 were analyzed by the proteomic technique MALDI-TOF MS and classified at the genus level 57% (165/286). For those that could not be identified by MALDI TOF-MS, selected isolates were identified by 16S rRNA gene (rrs) gene sequencing. The inference of the genus and/or species was possible in 97.7% (42/43) of the isolates. The most abundant genera identified were Pseudomonas, Ochrobactrum, and Bacillus. At the optimal salt concentration of 50 mM NaCl, the isolates P51 and P164, belonging to the genera Pseudomonas, provided an increase in most parameters related to rice seed germination analyzed, as compared to the non-inoculated treatment. Isolates B231, B67, and B143 related to the genus Bacillus promoted root elongation and a higher number of tips. At the stressing concentration of 200 mM, isolates B231 and B294, related to Bacillus provided an increase in the total length of roots compared to the non-inoculated treatment. These results confirm that the rhizosphere of halophyte plants represents a promising environment for the isolation of halotolerant and halophilic bacteria and that halotolerant bacteria from the genera Pseudomonas and Bacillus can promote the germination and initial development of rice seeds in the presence or absence of salt stress.