Abstract
The aim of this study was to investigate nitrificat ion activity of urea and the assimilation of nitrat e in a well aerated soil using perfusion technique with additio n of glucose as an energy and carbon source. In thi s study, urea was rapidly nitrified by the bacteria i n the saturated soil but its course of transformati on to NO 3 was not linear. There was an initial increase in th e concentration of nitrite during the nitrification experiment which indicated that the conversion of n itrite to nitrate was appreciably slower than the r ate of conversion of urea to nitrite. The rate of conversi on of NH 4 + to NO 2 - was faster than the rate of conversion of NO 2 - to NO 3 - in the first 12 days and as a result the nitrate c oncentration reached 2.72 µg/ml on the 12 th day. After day 12, the concentration of NH 4 + in solution declined significantly and the rate of conversion of NO 2 - to NO 3 - became faster than the rate of conversion of NH 4 + to NO 2 - . The concentration of NO 2-N in the solution reached zero on the 23 rd day. The nitrification curve has the character of a sigmoid curve whose midpoint, which representing the most rapid rate of nitrification, fell at the point of half conversio n of urea to nitrite. The curve asymptotically approaches a n itrate value that represents 98% conversion of urea into nitrate. The rest of the urea (NH 4) has presumably been synthesized into bacterial ce lls. The initial pH of the soil was 7.7 due to the presence of NH 4 which decreased gradually due to the production of NO 3 reaching 6.9 by day 23. A nitrate reduction was observed und er aerobic conditions. Denitrification did not proc eed according to the known fact that O 2 prevents the denitrifying organisms from producing the enzyme responsible for the process. The alternative pathway for nitrate reduction could be by assimilatory reduction where nitrate was converted to ammonium and then to cells. The removal of nitrate and production of ammonium caused a rise in the pH. The initial pH of the solution was 6.9 which increased with time reaching 7.3 by the 7 th day. The expected nitrate reduction was 50% accord ing to the assumption, but the 59% nitrate reduction observed in the experiment su ggests that more than 25% of glucose C was metabolized and less than 75% was oxidized, otherwise.
Highlights
The overall transformations of nitrogen in which microorganisms are involved range from nitrogen gas to protein and other complex organic nitrogenous compounds with a tremendously large array of substrates between these extremes (Figure 1)
There was an initial increase in the concentration of nitrite during the nitrification experiment which indicated that the conversion of nitrite to nitrate was appreciably slower than the rate of conversion of urea to nitrite
The nitrification curve has the character of a sigmoid curve whose midpoint, which representing the most rapid rate of nitrification, fell at the point of half conversion of urea to nitrite
Summary
The overall transformations of nitrogen in which microorganisms are involved range from nitrogen gas to protein and other complex organic nitrogenous compounds with a tremendously large array of substrates between these extremes (Figure 1). Protein P r o tei nas es → Peptides P ep tid ase s→ Amino Acid (1). Amino acids are either utilized as nutrients or degraded by microorganisms in a process called deamination. Deamination is the process of removing amino group with the production of ammonia and organic acids. The production of ammonia is referred to as ammonification (Fuka et al, 2009; Jetten, 2008; Hofmockel et al, 2010). An example of specific deamination-ammonification is as follows: CH3CHNH2COOH
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