Survey of Bacteria in the Farm of Faculty of Agriculture ,Al-Azahr University, Assiut Governorate,Egypt

Said A.M. El-Sayed

Two hundred and fifteen  soil bacteria isolates able to reduce NO-3, 210 produced nitrous oxide (N2O), even  only 47 were respiratory denitrifiers  . Nitrite or NH+4 was the major product of NO-3 reduction by the non-denitrifying organisms, but typically about 5 to 10% and up to 34% of the NO-3  reduced by them was released as N2O during a 2- week incubation period. Bacillus and Enterobacter were the most commonly observed genera of non-denitrifying N2O producers. Fermentative NO-2reduction and N2O production by a Bacillus sp. and a Citrobacter sp. were characterized in pure culture studies. Dinitrogen (N2) was not produced in detectable quantities by these organisms. When added to autoclaved soil, they accumulated more N2O than two denitrifying pseudomonads, since the latter consume and produce N2O. In tryptic soy broth (TSB), which allows active fermentative growth, NH+4 was apparently the major product of NO-3 reduction.  Added NH+4 did not inhibit N2O production or apparent reduction to NH+4, indicating that these processes are not essimilatory  . The effect added glucose on N2O production varied with the organism and media composition. Nitrous oxide production from NO-2 by these organisms was shown to be at least partially a biochemical reaction. The N2O evolved slowly in bath cultures and mostly after apparent growth ceased. This is apparently a novel mechanism of N2O generation which differs significantly from respiratory denitrification .


Key words: Nutrient broth (NB), tryptie soy broth (TSB), nitrite reduction, denitrification, dissimilatory ammonium production.