Endophytic establishment of the soil isolate Burkholderia sp. CC-Al74 enhances growth and P-utilization rate in maize (Zea mays L.)

Bacteria are common inhabitants of the rhizosphere or as endophytes in internal plant tissues. Among many bacterial genera, Burkholderia is a genus rich in nitrogen-fixing and phosphate-solubilizing strains that have been isolated from various plant systems. The function of phosphate-solubilizing bacteria in agriculture has been well documented, including enhancements in growth, yield and disease-resistance of crops. However, their response when introduced into a plant system in vitro is poorly studied. Inoculation of Burkholderia sp. CC-Al74, a phosphate-solubilizing soil isolate, on maize seeds resulted in the persistent endophytic establishment as determined by PCR detection method using Burkholderia-specific 16S rRNA gene primers. Burkholderia sp. CC-Al74-inoculated maize showed significant increases in plant height, plant biomass and root length, of about 45%, 48% and 86%, respectively, as compared to non-inoculated controls. After endophytic establishment, inoculated maize seedlings showed 2.4-fold increase in P-utilization rate in planta as well as an increased rhizosphere phosphatase activity as compared to the non-inoculated control. Nutrient analysis of inoculated maize showed 150% and 90% higher contents of P and N as compared to the non-inoculated control, respectively. Multilocus sequence typing (MLST) analysis showed that Burkholderia sp. CC-Al74 had a unique Sequence-Type, ST-730, which was novel when compared with existing STs in the MLST database. The phylogeny produced by recA sequence and MLST data revealed that Burkholderia sp. CC-Al74 is a novel member of Burkholderia cepacia complex. In summary, we provide direct evidence, which shows that the soil isolate Burkholderia sp. CC-Al74 could improve P-utilization rate as well as total P and N contents post-endophytic colonization in maize in vitro.