Análise proteômica de estirpes selvagem PAL5T e mutante lao- de Gluconacetobacter diazotrophicus na presença e ausência de triptofano e o efeito de sua inoculação em plantas micropropagadas de cana-de-açúcar

Abstract

The objective of this study was to evaluate the protein profile expression of G. diazotrophicus PAL5 and its defective mutant in the indole compound production (lao-) grown in the presence or absence of tryptophan through 2DE-PAGE technique. The spectrometric analysis allowed the identification of 24 differentially expressed proteins. The majority of the proteins down regulated in the wild type PAL5 cultivated with tryptophan as compared to the cultivation without the amino acid belonged to the category of transductional modification, protein turnover and chaperones. For the mutant lao- grown in the same conditions, the majority of the proteins that presented differential expression belonged to the category of production and conversion of energy. In addition, the majority of the protein differentially expressed in the mutant lao- as compared to the wild-type PAL5 strains belonged to carbohydrates metabolism and transport. On the other hand, no proteins related to the tryptophan biosynthesis were detected in any condition, possibly due to the low yield of the proteins during the spectrometric analysis. Furthermore, mutants lao- and nif- of G. diazotrophicus were used for inoculation of micropropagated sugarcane plants in order to determine the influence of auxins produced by the bacteria in the plant growth promotion in comparison with PAL5. The first experiment, carried out in hydroponic conditions for 10 days showed a significant inoculation effect of the wild type on plant shoot. The other experiment was conducted in a period of 120 days in pots containing sand:vermiculite substrate fertilized with 30 and 60 ppm with ammonium sulphate enriched with 15N. The plants were inoculated in vitro with the wild type and mutants lao- and nif-, and the results showed a visual difference in the roots inoculated with PAL5 that showed higher volume suggesting a higher number of secondary roots and root hairs. On the other hand, the plants inoculated with the lao- mutant were ticker and showed lower number of secondary roots and root hairs. The shoot biomass of plants inoculated with PAL5 was higher than those inoculated with the mutant strains for both N dose, however the difference was not significant. Plants grown with 60 kg N dose and inoculated with the mutants showed lower accumulation of dry shoot mass than plants inoculated with the wild type strain. In conclusion, the present study showed the occurrence of several differentially expressed proteins either in the wild type strain or in the mutant lao- grown in LGI-P with and without tryptophan. The role played by these proteins in the metabolism of the bacteria requires additional studies, including different growth conditions. In addition, the inoculation of micropropagated sugarcane plants suggested a hormonal effect of the bacteria mainly on the root development e consequently in the N use efficiency. However, the size of the pots may have limited the plant development, suggesting that new experiments should be carried out in more appropriated conditions to confirm the influence of the indol production and the BNF during the association of the G. diazotrophicus and sugarcane plants