bi374 lab exam2

Countable plate range

30-300 colonies only

CFU/mL formula

colonies, dilution, volume factors

Gram stain order

CV, iodine, alcohol, safranin

Gram-positive result

retains purple, thick wall

Gram-negative result

turns pink, thin wall

Sulfur reduction

SO4 to H2S

Reduction environment

anaerobic only

Reduction locations

sewage, sediment, rumen

Sulfur oxidation needs

oxygen and water

Oxidation effect

releases H+, lowers pH

MacConkey grows

Gram-negatives only

PCA grows

all bacteria

Sauerkraut succession order

coliforms, Leuconostoc, Lactobacillus

Yogurt bacteria pair

S. thermophilus, L. bulgaricus

Lactic acid effect

raises H+, lowers pH

Actinomycete growth style

fungus-like, mycelium forming

Life cycle order

substrate, aerial, spores

Aerial hyphae trait

multigenomic, forms spores

Drying soil purpose

isolates resistant spores

Top genus

Streptomyces, antibiotic source

Mesophile range

10-45°C

Thymine dimer cause

UV light damage

UV repair methods

photoreactivation, excision repair

Spread plating purpose

isolate single colonies

Pour plating best for

microaerophilic organisms

Ammonification

proteins broken into ammonia

Nitrification

ammonia oxidized to nitrate

Denitrification

nitrate reduced to N2

Nitrogen fixation

N2 converted to ammonia

Nitrogenase

fixes atmospheric nitrogen gas

Durham tube

traps nitrogen gas produced

P. aeruginosa

positive control, full denitrification

E. coli

negative control, stops at nitrite

Nitrate reductase

nitrate to nitrite enzyme

N-free media

selects nitrogen fixers only

Sulfur Cycle

Sulfur oxidation

S compounds to sulfate

Starkey broth

uses elemental sulfur source

Thiosulfate broth

uses sodium thiosulfate source

Bromocresol purple

turns yellow when acidic

Sulfuric acid

lowers pH, causes yellowing

Acidithiobacillus

acid-loving sulfur oxidizer

Sulfate reduction

anaerobic, produces H2S

Desulfovibrio

primary sulfate reducing bacteria

Dissimilatory reduction

sulfate as electron acceptor

Wastewater sludge

inoculum source for lab

Food Microbiology

Floral succession

bacterial species change over time

Leuconostoc

early sauerkraut fermenter, heterolactic

Lactobacillus

late sauerkraut fermenter, acid-tolerant

Homolactic

produces only lactic acid

Pasteurization

kills pathogens before fermenting

Yogurt starter

Lactobacillus and Streptococcus cultures

Alcoholic fermentation

sugar to ethanol, CO2

Specific gravity

measures sugar via hydrometer

Saccharomyces cerevisiae

wine fermentation yeast

MacConkey agar

selects Gram-negative bacteria only

Antibiotic-Producing Bacteria

Actinomycetes

mycelium-forming antibiotic producers

Antibiosis

microbial competition via antibiotics

AIA

selective media for Actinomycetes

Air-drying

selects for spore formers

Zone of inhibition

clear ring, antibiotic works

Serial dilution

reduces bacterial concentration stepwise

Streptomyces

major antibiotic-producing genus

Indicator organisms

test antibiotic spectrum

Broad spectrum

kills Gram-positive and negative

3-way streak

purifies isolated colonies

Environmental Stress Response

Mesophile

grows 10-45°C optimally

Thermophile

grows 40-70°C optimally

Thymine dimer

UV-damaged adjacent thymines

Photoreactivation

light-based DNA repair

Penicillin G

targets Gram-positive cell wall

Streptomycin

targets 30S ribosome broadly

Novobiocin

inhibits DNA gyrase enzyme

Vancomycin

targets Gram-positive cell wall

Proton motive force

disrupted by pH extremes

Cardinal temperatures

min, optimum, max growth

Nitrogen Cycle

Ammonification

proteins broken into ammonia

Nitrification

ammonia oxidized to nitrate

Denitrification

nitrate reduced to N2

Nitrogen fixation

N2 converted to ammonia

Nitrogenase

fixes atmospheric nitrogen gas

Durham tube

traps nitrogen gas produced

P. aeruginosa

positive control, full denitrification

E. coli

negative control, stops at nitrite

Nitrate reductase

nitrate to nitrite enzyme

N-free media

selects nitrogen fixers only

Sulfur Cycle

Sulfur oxidation

S compounds to sulfate

Starkey broth

uses elemental sulfur source

Thiosulfate broth

uses sodium thiosulfate source

Bromocresol purple

turns yellow when acidic

Sulfuric acid

lowers pH, causes yellowing

Acidithiobacillus

acid-loving sulfur oxidizer

Sulfate reduction

anaerobic, produces H2S

Desulfovibrio

primary sulfate reducing bacteria

Dissimilatory reduction

sulfate as electron acceptor