Lab 7 - Soil Testing for Antibiotic Production Day 2 – Vocabulary

Vocabulary flashcards covering media types, colony picking, and nitrate reduction concepts from the Day 2 notes.

GYE (growth medium)

Medium that promotes luxuriant growth of Lactobacilli.

SAB (Sabouraud Dextrose Agar)

Medium that supports growth of filamentous bacteria and fungi (e.g., Streptomyces) and fungi.

TSA (Tryptic Soy Agar)

General-purpose agar that supports growth of many bacteria.

Fuzzy colonies

Colony morphology indicating fuzzy, possibly spore-forming growth; avoid opening plates to prevent spore release.

Soft agar

Semi-solid agar used to create lawns or for testing interactions with colonies.

Nitrate Reduction Test

Assay to determine if an organism reduces nitrate (NO3) to nitrite (NO2) or further to other nitrogen forms.

Nitrate reductase

Enzyme that reduces nitrate to nitrite in the first step of nitrate reduction.

NO3 to NO2

Initial reduction step: nitrate is reduced to nitrite.

Nitrite (NO2-)

Product of nitrate reduction; reacts with reagents A and B to form a red color.

Assimilatory nitrate reduction

Nitrate is reduced to ammonium for incorporation into organic molecules.

Dissimilatory nitrate reduction (nitrate respiration)

Nitrate serves as an electron acceptor and is reduced to nitrogen gases (N2, N2O) for energy.

Nitrate broth

Beef extract and potassium nitrate medium used to test nitrate reduction; includes an inverted Durham tube to trap gas.

Beef extract

Nutrient source in nitrate broth.

Potassium nitrate (KNO3)

Nitrate source in nitrate broth.

Inverted Durham tube

Small gas-trapping tube inside the nitrate broth used to detect gas production.

Nitrate Reagent A (Sulfanilic Acid)

Reagent A reacts with nitrite to produce a red color when nitrite is present.

Nitrate Reagent B (Alpha-naphthylamine)

Reagent B reacts with nitrite to produce a red color when nitrite is present.

Nitrous acid (HNO2)

Acid formed when nitrite reacts in the broth; participates in the color-forming reaction with reagents A and B.

Zinc addition

Zinc reduces any remaining nitrate to nitrite; if red appears after zinc, the test is not a positive nitrate reduction.

Denitrification

Biochemical process where nitrate is reduced to nitrogen gases (N2 or N2O).

Why use S. aureus in this test

S. aureus serves as an indicator lawn to detect antimicrobial activity from soil isolates. It is a common infection, so useful if the isolates exhibit antibacterial properties against it.