Fermentations

Microbial Species in Fermentation

Fermentation is a metabolic process carried out by microorganisms to convert substrates into various by-products. Different microbes are involved in the fermentation of wine/beer and milk products.

• Wine/Beer Fermentation: The primary organism is Saccharomyces cerevisiae (a yeast).

• Milk Fermentation: Common organisms include Lactobacillus bulgaricus and Streptococcus thermophilus.

Substrates and By-products:

• Wine/Beer: Substrate is sugar (glucose, fructose) from grapes or grains. By-products are ethanol (alcohol) and carbon dioxide.

• Milk: Substrate is lactose (milk sugar). By-products are lactic acid (mainly), which causes acidification.

Example: In yogurt production, Lactobacillus bulgaricus and Streptococcus thermophilus ferment lactose to produce lactic acid, resulting in a sour taste and thickened texture.

Alcohol Production in Soda Pop

When soda pop is made naturally, little to no alcohol is produced because fermentation is stopped early or conditions are not optimal for alcohol-producing microbes.

• Trap Purpose: The trap prevents contamination and allows carbon dioxide to escape without letting air in, which could spoil the fermentation.

Triple Scale Hydrometer

A triple scale hydrometer measures the density of liquids, often used to estimate alcohol content in fermentation.

• Scale Used: Typically, the Specific Gravity (SG) scale is used.

• Alcohol Calculation: Alcohol content is estimated by measuring the difference in SG before and after fermentation.

Formula:

Note: This is an estimate, not a direct measurement of alcohol.

Cheese and Yogurt Fermentation

Cheese and yogurt are produced by fermenting milk with specific inocula.

• Source of Inoculum: Yogurt is inoculated with live cultures of Lactobacillus bulgaricus and Streptococcus thermophilus. Cheese may use similar or additional bacteria.

• Acidity: Both products are acidic due to lactic acid production.

• Effect of Lactic Acid: Lactic acid lowers pH, causing milk proteins (casein) to coagulate, forming the texture of yogurt and cheese.

• Homofermentation: Refers to fermentation where only one major product (lactic acid) is produced. In yogurt and cheese, homofermentative bacteria convert lactose almost exclusively to lactic acid.

Example: Homofermentative Lactobacillus species produce lactic acid, leading to thickened, acidic yogurt.

Miscellaneous Microbiology Techniques

Gram Staining and Controls

Gram staining differentiates bacteria based on cell wall structure. Controls are used to ensure staining accuracy.

• Gram Control: Used to verify staining procedure.

• Control Organisms: Escherichia coli (Gram-negative, rod-shaped) and Staphylococcus aureus (Gram-positive, cocci).

Example: E. coli appears pink (Gram-negative), S. aureus appears purple (Gram-positive).

Micropipettor Use

Micropipettors are used to measure and transfer precise liquid volumes. The volume setting is interpreted from the display, usually in microliters (µL).

Streaking and Colony Definition

Streaking is a technique to isolate individual microbial colonies on agar plates.

• Purpose: To obtain pure cultures by separating cells.

• Colony: A visible mass of microbial cells derived from a single cell or group of identical cells.

Glyphosate and Microbial Interactions

Glyphosate Experiments

Glyphosate is a herbicide. Experiments were designed to study its effects on environmental microbes and those in the rumen of cows.

• Purpose: To determine if microbes can utilize glyphosate and how it affects microbial communities.

• Rumen Microbes: Aid in digestion for cows. If glyphosate affects these microbes, cows may suffer digestive issues.

• Glyphosate Structure: If microbes can use glyphosate, it may supply phosphorus, nitrogen, or carbon.

Media Design for Glyphosate Utilization

Media were designed to enrich for organisms capable of using glyphosate as a nutrient source.

• Glyphosate Supply: Depending on the media, glyphosate could supply phosphorus, nitrogen, or carbon.

• Growth Without Glyphosate: If other nutrients are present, microbes may grow without using glyphosate.

• Testing Glyphosate Use: Growth in glyphosate media does not confirm glyphosate utilization. Chemical analysis (e.g., sending samples to Chemistry) is needed to measure glyphosate depletion.

Kirby-Bauer Test

The Kirby-Bauer test assesses microbial sensitivity to antibiotics or chemicals.

• Purpose: To test glyphosate-resistant and sensitive organisms for susceptibility.

Surfactant Plate and Turbidity

Surfactant plates were used to distinguish effects of surfactants in RoundUp from glyphosate. Turbidity indicates microbial growth, but some microbes may grow without visible turbidity.

Dilutions and Microbial Calculations

Dilution Terminology and Calculations

Dilution calculations are essential for quantifying microbial populations.

• Dilution: The process of reducing concentration by mixing with a solvent.

• Total Dilution: The overall reduction after multiple steps.

• Dilution Factor: The ratio of final to initial concentration.

• Statistically Valid Plate Counts: Plate counts within a range (typically 30-300 colonies) are considered statistically valid.

CFU and Viable Cells

CFU stands for Colony Forming Unit, representing a viable cell capable of forming a colony.

• Viable Cell: A cell capable of reproduction.

• CFU Calculation: Used to estimate the number of viable cells in a sample.

Formula:

Concentration Calculations

Concentration conversions and solution preparation are common laboratory tasks.

• Percent to mM Conversion: Convert percent concentration to molarity (mM) using molecular weight.

• Solution Preparation: Use the formula to prepare solutions from stock.

Formula:

Example: To make 100 mL of a 10 mM solution from a 100 mM stock: , so .

Summary Table: Microbial Fermentation Organisms and Products

Summary Table: Gram Stain Control Organisms

Additional info: Academic context was added to clarify fermentation processes, microbial species, and laboratory calculations, ensuring completeness and self-contained study notes.