Nitrate reduction test

3 possibilities Nitrate – nitrate reductase – nitrite Nitrate – nitrate reductase – nitrite – Nitrite reductase – nitrogen gas Neither enzymes were produced by the bacterium – bacterium cannot use nitrate.

Some bacteria make only nitrate reductase Some bacteria make both nitrate reductase, nitrite reductase Some bacteria neither of the enzymes

Nitrite indicators are added to each tube. Medium becomes red – nitrite in the medium Bacterium produced nitrate reductase only. Add a pinch of zinc to those tubes that did not become red

Medium becomes red after adding zinc Zinc converted nitrate in the medium to nitrite – chemical reduction, not bacterial reduction. Bacteria did not use the nitrate. Therefore zinc was able to use it – convert it. Bacterium produced neither of the enzymes

No red color after adding zinc - bacterial reduction Bacteria made both nitrate reductase and nitrate reductase Nitrate – nitrite – nitrogen gas

Urea hydrolysis Urea – urease – ammonium ions Change the pH indicator to fuchsia

Litmus milk Lactose – milk sugar Casein – milk protein Litmus – pH indicator Acidic – pink Basic – blue Neutral - lavender

Streptococcus lactis Lactose – acids Acids then coagulate the milk protein Milk becomes a solid E. coli Not a strong acid producer as S. lactis Enough to change litmus to pink, but not enough to coagulate the protein

Pseudomonas aeruginosa Positive for peptonization ( protein hydrolysis). Casein – amino acids Milk becomes a brownish solution