Nitrate and nitrite reduction by microorganisms embedded in a filter paper incubated aerobically.

Pseudomonas aeruginosa, grown to steric saturation between the cellulose fibers of a filter paper, reduced nitrate or nitrite or both when the cell-filled paper was washed, transferred to phosphate buffer, nitrate, or nitrite or both, and glucose agar plates, and incubated under aerobiosis as resting cells. The biological nature of the reduction was ascertained by the use of nitrate and nitrite reductaseless mutants. The mesh of cellulose fibers was necessary to create a sufficient barrier to oxygen diffusion, since denitrification was not obtained within large and thick colonies of P. aeruginosa. When a soil suspension was used to inoculate the filter paper, ammonium and nitrite accumulated. Concomitant to nitrate reduction, the total nonvolatile inorganic nitrogen decreased and then increased as if part of it was immobilized to be subsequently mineralized.