Resumo

Endophytic bacteria are ubiquitous in most plant species. These bacteria reside latently or actively colonizing leaves, stems and roots apparently without causing any visible damage to their hosts. To isolated them is necessary a superficially sterilized tissue. Benefits of endophytic bacteria in plants were already demonstrated. Previous studies mentioned that the application of some microorganisms for beneficial purposes needs the knowledge of bacterial genes and traits involved in root colonization. However, this information cannot be extrapolated to endophytic colonization. Enterobacter cloacae strain 344 was chosen as a model in order to study the genes which determine endophytic colonization. This bacterium was isolated from healthy stem tissues of Theobroma cacao in southern Bahia – Brazil. Preliminary data suggest that it is involved in plant growth promoting, drought tolerance and induction of resistance to Moniliophthora perniciosa. To study the genes were constructed mutants with random insertion mutagenesis. The EZ::TN< KAN-2 > transposome complex, a mixture of the transposon EZ::TN < KAN-2 > and EZ::TN transposase was introduced by electroporation directly into Enterobacter cloacae 344 electrocompetent cells. There were 104 mutants generated. It was confirmed using the primer BOX A1-R. In the colonization bioassays in cucumber plants mutants with the wild type in competition are being tested. The seeds are superficially sterilized and after 24h are subjected to microbiolization being immersed for 5 min in bacterial suspensions that are composed for 1:1 mixture of each mutant and wild-type (344 strain) containing 10⁵ CFU / mL including a negative control. The seeds are transferred to ½ water agar test tubes at room temperature for a period of 7 days. The mutants with endophytic colonization significantly different from the wild type will be used to identify genes involved in colonization and sequence analysis of the disrupted genes. The 8 % of mutants was tested and partial results do not show significantly difference in colonization until now. This knowledge about the genes involved in endophytic colonization may contribute to generate efficient colonization isolates used in plants of economic interest.