Effect of nitrate and glucose addition on denitrification and nitric oxide reductase (cnorB) gene abundance and mRNA levels in Pseudomonas mandelii inoculated into anoxic soil

Abstract

The effect of glucose addition (0 and 500 μg C g(-1) soil) and nitrate (NO(3)) addition (0, 10, 50 and 500 μg NO(3)-N g(-1) soil) on nitric oxide reductase (cnorB) gene abundance and mRNA levels, and cumulative denitrification were quantified over 48 h in anoxic soils inoculated with Pseudomonas mandelii. Addition of glucose-C significantly increased cnorB(p) (P. mandelii and related species) mRNA levels and abundance compared with soil with no glucose added, averaged over time and NO(3) addition treatments. Without glucose addition, cnorB(p) mRNA levels were higher when 500 μg NO(3)-N g(-1) soil was added compared with other NO(3) additions. In treatments with glucose added, addition of 50 μg NO(3)-N g(-1) soil resulted in higher cnorB(p) mRNA levels than soil without NO(3) but was not different from the 10 and 500 μg NO(3)-N g(-1) treatments. cnorB(p) abundance in soils without glucose addition was significantly higher in soils with 500 μg NO(3)-N g(-1) soil compared to lower N-treated soils. Conversely, addition of 500 μg NO(3)-N g(-1) soil resulted in lower cnorB(p) abundance compared with soil without N-addition. Over 48 h, cumulative denitrification in soils with 500 μg glucose-C g(-1) soil, and 50 or 500 μg NO(3)-N g(-1) was higher than all other treatments. There was a positive correlation between cnorB(p) abundance and cumulative denitrification, but only in soils without glucose addition. Glucose-treated soils generally had higher cnorB(p) abundance and mRNA levels than soils without glucose added, however response of cnorB(p) abundance and mRNA levels to NO(3) supply depended on carbon availability.