Response of selected genes of burkholderia xenovorans strain lb400 to onion extract using a DNA:RNA hybrid capture detection system*

Burkholderia xenovorans strain LB400 was exposed to Allium cepa (onion) extract to investigate the expression of selected putative genes including four polychlorinated biphenyls (PCBs) degrading genes ibphA, bphE, bphF and bphG). B. xenovorans strain LB400 is renowned for its appetite towards the most difficult to degrade compounds in soil. Onion, medicinally important as well as antibacterial and antifungal plant, was used in this study to further investigate the nutritional versatility of LB400. A cDNA microarray containing Polymerase Chain Reaction (PCR) products of 530 selected genes of LB400 was prepared. Total RNAs isolated from LB400 cells grown in minimal medium (M9) and minimal medium supplemented with 1% onion extract (M90) were used as targets for hybridization to the LB400 array. A novel DNA-RNA detection system with indirect labeling was used to obtain the mRNA abundance under the two conditions. Approximately, 12% of the total genes included on the array were expressed significantly above the background level in M9 while more than 36% were expressed in M90. Comparing the transcripts expression in M90 to M9 identified the difference in the expression level of about 60 genes including bphA, bphE and bphG. Further, it was observed that onion extract enhanced the growth of LB400. Approximately, 30% increase in the growth rate of LB400 was observed due to the addition of onion extract in M9 compared to M9 without onion extract, at both 24 and 48 h after the inoculation. Hybridization analyses using varying amounts of total RNA also revealed a linear correlation between the amount of targeted RNA (1, 5 and 10 ug of total RNA) and signal intensity of the hybridized genes. These results indicate that onion extract has the potential to support and enhance the growth of B. xenovorans strain LB400, as well as positively regulate the expression of PCBs degrading genes. Further, LB400 maybe a virulent pathogen of onion.