McCarty G W, Bremner J M
Environmental Chemistry Laboratory, U.S. Department of Agriculture-Agricultural Research Service, Beltsville, MD 20705.
Proc Natl Acad Sci U S A. 1993 Oct 15;90(20):9403-7. doi: 10.1073/pnas.90.20.9403.
Although it has been demonstrated that Mn2+ and Mg2+ can influence the activity of glutamine synthetase in various organisms, there is little information concerning the effects of these cations on the activity of this enzyme in soil microorganisms or on ability of these microorganisms to assimilate NO3- and NH4+. We studied the effects of different concentrations of Mn2+ and Mg2+ on assimilatory NO3- reduction and NH4+ assimilation in cultures of two microorganisms commonly found in soil [Pseudomonas fluorescens (ATCC 13525) and Azotobacter chroococcum (ATCC 9043)] and in an enrichment culture of soil microorganisms. We found that Mn2+ strongly inhibited NH4+ assimilation by soil microorganisms and blocked the inhibitory effect of NH4+ on assimilatory NO3- reductase (ANR) activity, thereby uncoupling ANR activity from nitrogen assimilation 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 these cations on nitrogen assimilation by soil microorganisms will depend on the ratio of their concentrations in soil.
尽管已经证明锰离子（Mn2+）和镁离子（Mg2+）能够影响多种生物体中谷氨酰胺合成酶的活性，但关于这些阳离子对土壤微生物中该酶活性的影响，以及对这些微生物同化硝酸根离子（NO3-）和铵根离子（NH4+）能力的影响，相关信息却很少。我们研究了不同浓度的Mn2+和Mg2+对两种常见于土壤中的微生物[荧光假单胞菌（ATCC 13525）和褐球固氮菌（ATCC 9043）]以及土壤微生物富集培养物中同化性硝酸根还原和铵根同化的影响。我们发现Mn2+强烈抑制土壤微生物对NH4+的同化，并阻断了NH4+对同化性硝酸根还原酶（ANR）活性的抑制作用，从而使ANR活性与氮同化解偶联，并导致ANR活性形成的NH4+释放到环境中。Mg2+抵消了Mn2+对微生物氮代谢的影响，这表明这些阳离子对土壤微生物氮同化的总体影响将取决于它们在土壤中的浓度比例。
