Recovery of useful traits from isolates inhabiting an agricultural soil cultivated with herbicide-resistant poplars

The aim of this study was to investigate the culturable bacteria living in soil cultivated with Basta-tolerant transgenic white poplars (Populus alba L. 'Villafranca'). Plate Count Agar medium containing phosphinothricin, the active component of Basta, was used to isolate the herbicide-resistant bacteria (HRB). No significant changes in the size of the soil microbial flora following herbicide treatment were observed. The characterization of HRB isolates by 16S rDNA-based taxonomy revealed a predominance of Pseudomonas and Bacillus species. The screening carried out on soil samples allowed for the recovery of isolates with useful properties for biotechnological and agronomical purposes, particularly in relation to root development. Among the tested isolates, only HRB-1b, HRB-1c, and HRB-7 showed remarkable swarming ability, a valuable trait supporting the beneficial plant-microbe interactions. HRB-1c was also characterized by consistent production of indoleacetic acid (17.8 +/- 0.09 microg x mL-1 x (OD600 unit)-1), and it was able to stimulate the in vitro growth of Villafranca explants. Since novel tools are constantly required to enhance productivity of perennial species and to expand their use for practical purposes, the availability of bacteria that support tree growth, such as the HRB-1c isolate, represents a significant advantage