Actinomycetes In The Soil To Participate In The Study Of The Possibility Of Denitrification

For a long time, bacteria have been regarded as the only responsible organisms for denitrification. Recently a few reports indicated that actinomycetes in pure culture could reduce ¹⁵NO₃^– to ¹⁵N₂O. These actinomycetes belong to 11 genera and most of them are Streptomyces.Twenty three single colonies of actinomycetes were isolated from a soils ample collected from Changshu Agroecological Experimental Station, Institute of Soil Science, Chinese Academy of Sciences. Among 10 strains distinguished from each other by morphological properties, 9 were further identified as Streptomyces sps. All strains showed capability of reducing nitrate into N₂O under anaerobic pure culture conditions. Three strains were selected and denitrification rates were measured. Nitrous oxide production rate of these strains ranged from N 1.2 to187.7μg g–1min–1. The strains were shown not only to grow well but also to be able to reduce nitrate to N₂O in sterile soil, indicating that these strains were able to use soil organic carbon as electron donor for nitrate reduction. Acetylene showed inhibitory effect on N₂O production of most strains isolated. Stressed under continuous strict anaerobic condition, strains of Streptomyces sps still showed considerable denitrification capacities.A number of single colonies of actinomycetes were isolated from soils samples collected in Suzhou and were checked by the gfp–reporter method developed in collaboration with Cornell University. It was confirmed that the 5# strains could produce NO.Denitrifying enzyme can be released out of the cells and adsorbed to soil particles. The existing methods of measuring soil denitrifying activity do not distinguish sources of denitrification from extracellular and intracellular enzymes. However, many studies showed that denitrifying bacteria and denitrifying activity is not always correlated. It is therefore worthwhile distinguish the contribution of extracellular and intracellular denitrifying enzymes to soil denitrification activities. Agrobacterium tumefaciens C58 was cultured in NB medium, centrifuged and washed. The cell concentration was determined. The measured denitrifying activity of pure cells was converted to the denitrifying activity per cell. In addition, Agrobacterium tumefaciens C58 (AT) was inoculated into soils, NB medium added and grow for a period of time. The cell number in the soil at the end of incubation was determined. In the mean time, the soil containing the in situ grown cells were determined for their denitrifying activity. The activity was converted into specific activity according to the number of cells in soil measured. Comparing the results obtained from the two methods stated above, it was shown that extracellular enzyme contributed significant portion of denitrifying activity as measured by conventional method.