BIO 204 Lecture 8 — Bacterial Diversity & Food Microbiology

What three processes cause new bacterial species to diverge, emerge, and evolve over time?

Changes in the DNA genome, natural selection, and degenerative evolution.

How do different environments increase bacterial diversity?

They enforce different selective pressures on the microbes living there.

What factors increase bacterial diversity over time?

Changes in DNA, natural selection, degenerative evolution, and environmental selective pressures.

Why can different environments lead to different bacterial traits?

They enforce different selective pressures.

Can closely related bacterial species have very different characteristics?

Yes, even closely related species and strains can be profoundly different.

How similar can two bacterial species be genetically while having different effects on humans?

They can share greater than 97% genome sequence identity.

What example shows that closely related bacteria can have very different human effects?

Harmless Bacillus thuringiensis versus Bacillus anthracis, which causes anthrax.

Do most bacterial species have a positive or negative impact on humans?

Most bacterial species have a positive impact.

What are two positive impacts bacteria can have?

Shaping ecosystems and contributing to the human body microbiome.

How can bacteria negatively affect humans?

Pathogens can cause disease and excrete harmful toxins or compounds.

Bacteria contributing to our microbiome is an example of what type of impact?

A positive impact.

A bacterium causing disease or releasing toxins is an example of what type of impact?

A negative impact.

What is bacterial taxonomy based on?

Sequence homology and trait similarity.

Which taxonomic levels does BIO 204 Lecture 8 focus most heavily on?

Genus and species.

How much diversity can exist at the genus and species levels?

A great amount; closely related species can have profoundly different traits.

How are formal names of phyla, classes, orders, and genera written?

They are capitalized.

How are genus and species names written?

They are italicized.

How are informal bacterial names and adjectival forms written?

They are written in lowercase.

What is the standardized format for a bacterial name?

Genus species.

What formatting is expected for a formal bacterial genus and species name?

The genus is capitalized, and both genus and species are italicized.

What is an example of proper bacterial naming?

Streptococcus pyogenes or Bacillus anthracis.

What are fermented foods?

Food products modified biochemically by microbial growth.

What are the three main benefits of fermentation in food production?

Improved digestibility, added nutrients/flavors, and food preservation.

How does fermentation improve digestibility?

Complex macromolecules are broken down into smaller, easily digested segments.

How does fermentation add nutrients and flavors?

Microbial metabolism generates vitamins and flavor molecules as byproducts.

How does fermentation help preserve food?

Acid buildup prevents the growth of competing microbes.

Why are acids produced during fermentation useful for food preservation?

They restrict microbial growth.

What are we establishing when we make fermented foods?

Controlled microbial ecosystems for our own nutrition.

What starting material is used to make fermented dairy products?

Liquid milk.

What does microbial fermentation of liquid milk produce?

Solid products such as cheese, yogurt, and cottage cheese.

What causes milk proteins to coagulate into curd and separate from whey?

Acid production.

What determines the final fermented dairy product?

The species of bacteria or mold and the degree of fermentation.

What happens during first-stage dairy fermentation?

Glucose is fermented into lactic acid.

What bacteria often perform first-stage dairy fermentation?

Lactobacillus bacteria.

What happens during second-stage dairy fermentation?

Lactic acid is fermented into propionic acid.

What bacteria often perform second-stage dairy fermentation?

Propionibacterium bacteria.

What food is associated with fermentation of lactic acid to propionic acid?

Swiss cheese.

Glucose → lactic acid is associated with what type of dairy fermentation?

First-stage fermentation.

Lactic acid → propionic acid is associated with what type of dairy fermentation?

Second-stage fermentation (used in Swiss cheese).

What type of microbe is used mostly for bread-making fermentation?

Yeast, a eukaryotic microbe.

What is baker's yeast?

Saccharomyces cerevisiae.

What is a sourdough starter?

A homemade culture of wild yeasts and bacterial species.

What are the main starting materials for yeast-based bread fermentation?

Starch and glucose in flour.

What does yeast do during bread-making?

It breaks starch into simple sugars, which ferment to produce CO2.

What is the main fermentation product emphasized for bread-making?

Carbon dioxide (CO2).

Why is flour important in bread-making?

It provides structural proteins and sugars needed for fermentation.

What is the purpose of yeast in bread-making?

To break down starch into simple sugars and produce CO2 via fermentation.

Saccharomyces cerevisiae fermenting flour sugars to produce CO2 describes what process?

Bread-making fermentation.

What type of microbes perform ethanolic/alcoholic fermentation in beer and wine?

Yeast.

What yeast is commonly used for beer fermentation?

Strains of Saccharomyces cerevisiae.

What is beer produced by alcoholic fermentation of?

Grain.

What happens to grain during beer production before fermentation?

Grains are germinated and mashed, breaking starch into maltose.

What does yeast produce from glucose during beer fermentation?

Ethanol and CO2.

What is wine produced by alcoholic fermentation of?

Fruit, most often grapes.

What sugars are present in high concentrations in fruit?

Simple sugars such as glucose and fructose.

What does yeast produce during wine fermentation?

Ethanol and CO2.

What is the major difference between beer and wine fermentation?

Beer requires breaking down grain starch; fruit for wine already contains simple sugars.

Why is wine fermentation quicker than grain fermentation?

Simple sugars in fruit are immediately available for fermentation.

Grain + yeast → ethanol and CO2 describes the production of what?

Beer.

Fruit sugars + yeast → ethanol and CO2 describes the production of what?

Wine.

What is food spoilage?

Spoilage resulting from normal microbial growth on food.

What happens when excess microbes grow in food?

Nutrients decrease and toxins increase.

What observable changes can indicate food spoilage?

Changes in form, texture, color, smell, and taste.

What is perishable food?

Food capable of spoiling due to microbial growth.

What is food contamination?

Contamination by pathogens that usually causes gastrointestinal illness.

How much pathogenic microbe is required for food contamination to cause illness?

Only a small amount.

What is the major difference between food spoilage and food contamination?

Spoilage alters food via normal growth; contamination involves pathogens causing illness.

Can any type of food become contaminated?

Yes.

What physical processes can prevent food spoilage and contamination?

Dehydration/freeze-drying, refrigeration/freezing, pasteurization, canning, and ionizing radiation.

What chemical processes can prevent food spoilage and contamination?

Acids, organic compounds, and inorganic compounds.