Gw. Mccarty et Jm. Bremner, EFFECTS OF MN2- AND NH4+ BY SOIL-MICROORGANISMS( AND MG2+ ON ASSIMILATION OF NO3), Proceedings of the National Academy of Sciences of the United Statesof America, 90(20), 1993, pp. 9403-9407
Although it has been demonstrated that Mn2+ and Mg2+ can influence the
activity of glutamine synthetase in various organisms, there is littl
e information concerning the effects of these cations on the activity
of this enzyme in soil microorganisms or on ability of these microorga
nisms to assimilate NO3- and NH4+. We studied the effects of different
concentrations of Mn2+ and Mg2+ on assimilatory NO3- reduction and NH
4+ assimilation in cultures of two microorganisms commonly found in so
il [Pseudomonas fluorescens (ATCC 13525) and Azotobacter chroococcum (
ATCC 9043)] and in an enrichment culture of soil microorganisms. We fo
und that Mn2+ strongly inhibited NH4+ assimilation by soil microorgani
sms and blocked the inhibitory effect of NH4+ on assimilatory NO3- red
uctase (ANR) activity, thereby uncoupling ANR activity from nitrogen a
ssimilation and causing the NH4+ formed by ANR activity to be released
to the environment. Mg2+ counteracted the effect of Mn2+ on microbial
metabolism of nitrogen, which suggests that the overall effect of the
se cations on nitrogen assimilation by soil microorganisms will depend
on the ratio of their concentrations in soil.