Bradyrhizobium japonicum mutant lacking LPS is more sensitive to detergent than wild type

초록

Bradyrhizobium japonicum is a nitrogen fixation bacterium capable of forming nodules in soybeans. In previous studies, lipopolysaccharide(LPS) minus knock-out mutant(JS314) which failed to form nodules was isolated. Our hypothesis is that for successful symbiotic infection into soybean roots, B. japonicum should withstand a number of plant defense compounds such as antibacterial plant peptides and plant detergents. In this study, JS314 was compared with wild type in terms of their sensitivity to detergents, tween 80 and sodium deoxy cholate(SDC). Both strains were incubated in the presence of tween 80 (2%,4%,6% and 8%) and growth was monitored by measuring OD600 at time intervals. Also the number of survived cells following treatment with SDC(0.02%,0.05% and 0.1%) for 1 minute was plate counted. After three day incubation with tween 80, only wild type strain kept growing while JS314 stopped growing. SDC treatment also differentially affected the growth; at each concentrations, JS314 was 20~30% less survived in SDC. It is likely that LPS of B.japonicum is working as a physical barrier resistant to antibacterial compounds during infection in soybean. Further studies are underway to examine other plant antibacterial compounds such as plant peptides.