There are generally two explanations for the observation; 1. The nitrate should not be reduced, the strain is considered as nitrate-negative. 2. The nitrative can be reduced into nitrite that have been completely reduced into the nitric oxide or nitrous oxide or in the form of nitrogen which on reacting with nitrogen produces a nitrate-positive
Abstract. The intestine is inhabited by a large microbial community consisting primarily of anaerobes and, to a lesser extent, facultative anaerobes, such as Escherichia coli, which we have shown requires aerobic respiration to compete successfully in the mouse intestine (S. A. Jones et al., Infect. Immun. 75:4891-4899, 2007). Nitrate and nitrite reduction are of paramount importance for nitrogen assimilation and anaerobic metabolism, and understanding the specific roles of each participating reductase is necessary to describe the biochemical balance that dictates cellular responses to their environments. The soluble, cytoplasmic siroheme NADH-nitrite reductase (Nir) in Escherichia coli is necessary for nitrate
Most of the E. coli wild-type strains contain both nitrate and nitrite reductase [24] as E. coli MC 1061. This represented a problem for these test purposes, since the latter enzyme could interfere with the determination of nitrate and nitrite by lowering the actual nitrite concentration in the biological samples tested.
If neither a red color or gas is observed, then, confirmation is necessary that nitrate (NO 3) remains in the broth. A SMALL addition of zinc dust will convert the nitrate to nitrite and form a red color. This test reaction is considered negative for nitrate reduction. Nitrate reductase (+) = red after reagent A & B added
Incubate at 35-37°C for 18-24 hours. (sometimes incubation of 4 days is required) Phase 1: Directly add 0.1 m of reagent to the nitrate culture. If red color is seen within 30 seconds, the test is positive. Proceed to phase 2 if phase 1 is negative. Phase 2 (zinc reduction method): Add 20 grams of zinc dust to the test tube.
In E. coli O 2 represses all anaerobic respiratory pathways and fermentation, whereas nitrate is the preferred acceptor under anaerobic conditions and represses other anaerobic pathways 5, 9, 11, 44. The hierarchy is effected by transcriptional regulation of the corresponding terminal reductases by O 2 and nitrate. ALAztr.
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    • e coli nitrate reduction test