Use of antibiotics to control endophytic bacterial growth migration onto culture medium in Eucalyptus cloeziana F.Muell.: a micropropagation approach

The natural endophytic bacterial growth migration onto a culture medium is commonly associated with unnecessary microplant discards. In micropropagation procedures, some bacteria can exude from the internal tissues of plants to colonize the culture medium and compete with the plants for nutrients, which may lead to a reduction in plant development. To find an efficient antibiotic protocol to control this bacterial growth migration onto the culture medium without affecting plant development, Eucalyptus cloeziana F.Muell. microstumps were subjected to four antibiotic treatments for 30 d. They were treated with gentamicin, ciprofloxacin, rifampicin, or Timentin®, in addition to the control treatment (antibiotic free). The effects of the antibiotics were monitored weekly, and the endophytic bacterial community structures were evaluated in two periods of plant development (15 d and 30 d).The denaturing gradient gel electrophoresis (DGGE) technique was used to compare the control and post-antibiotic treatment plant microbiological composition, to determine if the antibiotic treatment played a specific role on the endophytic bacterial community structure. The gentamicin treatment was composed of a distinct community from the control treatment. Nonetheless, the plants treated with ciprofloxacin and rifampicin manifested similar endophytic community structures compared to the control. In contrast, plants treated with Timentin® showed a specific bacterial community composition and a higher plant dry mass, number of shoots, and nutritional content. These results suggested that Timentin® treatment could be applied for 30 days to control endophytic bacterial growth migration onto the culture medium, without affecting the homeostatic balance between the bacteria and plants.