Effects of Various Inhibitors on Nitrate Uptake Mediated by Bacillus sp. GS2

Abstract

Nitrate is one of the major components causing salt stress in Korean farm lands. In order to remove the excess amount of nitrate from the cultivating soils, soil bacteria having nitrate uptake activity were isolated. One of them showed a high capability of nitrate uptake. In the PCR analysis, 1373 bp of 16S rRNA gene were sequenced and compared to those of various microorganisms. The strain has identified as Bacillus sp. GS2. Growth of GS2 was not much facilitated by nitrate; however, high capacity of nitrate uptake was measured by removing 40 mM nitrate within 12 h. Nitrate transporter and nitrate reductase are useful enzymes to remove excess soil nitrate. GS2 showed high activity of nitrate reductase and the amount of nitrite formation was directly proportional to the amount of nitrate uptake. In order to characterize the bacterial nitrate uptake, the effect of chlorate was measured on the nitrate uptake activity of GS2 since chlorate was reported to inhibit nitrate transporter. While bacterial growth was not much inhibited by chlorate, the nitrate uptake was inhibited by 80% at the concentration of 50 mM chlorate. The effects of vanadate and phenylglyoxal (PGO) were measured on nitrate uptake. Both vanadate and chlorate showed similar patterns of inhibition on nitrate uptake and 50% inhibitions were obtained at 10-30 mM. PGO, an inhibitor of microbial nitrate transporter, completely inhibited the nitrate uptake at 1 mM. These results suggest that the nitrate reduction by GS2 is mediated by both membrane nitrate transporter and nitrate reductase in cytosol rather than by periplasmic enzyme.