Figure 3

Association of Burkholderia Q208 with sugarcane roots.

(a) Electron microscopy of the sugarcane roots inoculated with Burkholderia Q208 and the abundance of Burkholderia on the root surface, compared to the endophytic bacteria. a1 – TEM of the bacterial culture used for the inoculation; a2 – SEM of the sugarcane roots with a box indicating the magnified area shown in a3. The plants were grown in gnotobiotic conditions for 5 days. Arrows indicate bacteria, white arrowheads-plant cell wall, black arrowheads-blanket-like material covering Burkholderia cells. a4 –quantitative real-time PCR showing relative abundance of Burkholderia outside of the roots (rhizospheric) and inside of the roots (endophytic). Black bars display the results of the qRT PCR carried out on the roots with bacteria, and white bars the roots only, with root-associated bacteria stripped off. Abundance of 16S rRNA genes of Burkholderia was quantified relatively to 25S rRNA genes of sugarcane. Data represent averages of three independent replicates. *** indicates significant difference at P < 0.001 (Student’s t test). (b) Biofilm formation assay for the conditions when Burkholderia were grown in the nutrient medium without (1) or with (2) addition of sugarcane root extract. Blue color indicates formation of the biofilm, when crystal violet staining is applied to the media (top panel); the absorbance quantification of 7 biological replicates are shown (bottom panel). The bars represent SD. ** indicates significant difference at P < 0.01 (Student’s t test).