Transcript Lab Nitrate reduction test

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