I. INTRODUCTION

A. INTRODUCTION TO MICROBIOLOGY

Fundamental Statements for this Learning Object:

1. Microorganisms are typically too small to be seen with the naked eye.
2.  Bacteria, fungi, viruses, protozoa, and algae are the major groups of microorganisms.
3. The vast majority of microorganisms are not harmful but rather beneficial.
4. Microbiota refers to all of the microorganisms that live in a particular environment.
5. A microbiome is the entire collection of genes found in all of the microbes associated with a particular host.
6. The microbiome of the human body - especially in the intestinal tract - aid in the digestion of many foods, the regulation of multiple host metabolic pathways, and the regulation the body's immune defenses.
7. Symbiosis is the living together of two dissimilar organisms. Mutualism is a symbiotic interaction between different species that is mutually beneficial whereas commensalism is a symbiotic interaction between different species where one organism lives on or within another organism,and derives benefit without necessarily harming or benefiting the host.

LEARNING OBJECTIVES FOR THIS SECTION

Basic Groups of Microbes

Microorganisms are the dominant life forms on earth, are found in almost every conceivable environment, and are essential to sustaining life on this planet. There are 5 basic groups of microorganisms:

a. Bacteria

Bacteria are typically unicellular, microscopic, prokaryotic organisms that reproduce by binary fission (see Fig. 1 and Fig.2).

b. Fungi: yeasts and molds

Yeasts are typically unicellular, microscopic, eukaryotic fungi that reproduce asexually by budding (see Fig. 3 and Fig. 4).

Molds are typically filamentous, eukaryotic fungi that reproduce by producing asexual reproductive spores (see Fig. 5 and Fig. 6)

c. Viruses

Viruses are typically submicroscopic, acellular infectious particles that can only replicate inside a living host cell. The vast majority of viruses possess either DNA or RNA but not both (see Fig. 7 and Fig. 8).

d. Protozoa

Protozoa are typically unicellular, microscopic, eukaryotic organisms that lack a cell wall (see Fig. 9 and Fig. 10).

e. Algae

Algae are typically eukaryotic microorganisms that carry out photosynthesis (see Fig 11 and Fig. 12).

 

 

To view a nice interactive illustration comparing size of cells and microbes, see the Cell Size and Scale Resource at the University of Utah. (Genetic Science Learning Center. (2010, September 2) Cell Size and Scale. Retrieved October 19, 2017, from http://learn.genetics.utah.edu/content/cells/scale/ )

YouTube movie illustrating Size Comparison of Microorganisms created by Gracia Alvaro Montoya, MetaBallsStudios (MBS), United Kingdom, Nov., 2017

To get us started on our introduction of microorganisms we will go through the following Think-Pair-Share Questions.

In this course we will be looking at various fundamental concepts of microbiology, with particular emphasis on their relationships to human health. The overall goal is to better understand the total picture of infectious diseases in terms of host-infectious agent interaction. We will look at various groups of microbes and learn what they might do to establish infection and harm the body, we will look at the body to see the ways in which it defends itself against these microbes, and we will learn what can be done to help the body in its defense efforts.

Most people tend to think of microorganisms as harmful because of their roles in causing infectious diseases in humans and other animals, and agricultural loss as a result of infectious diseases of plants and the spoilage of food. The fact is, however, the vast maority of microorganisms are not harmful but rather beneficial. Without them there would be no life on earth. Therefore, we will start this course by looking at a few of the many benefits from microbial activity on this planet.

1. Food production

Many food products employ microorganisms in their production. These include the microbial fermentation processes used to produce yogurt, buttermilk, cheeses, alcoholic beverages, leavened breads, sauerkraut, pickles, and kimchi.

2. Energy production and cleaning up the environment

Methane, or natural gas, is a product of methanogenic microorganisms. Many aquatic microbes capture light energy and store it in molecules used as food then used by other organisms. Animal wastes, domestic refuse, biomass, and grain can be converted to biofuels such as ethanol and methane by microorganisms. In addition, through a process called bioremediation (def), some pollutants such pesticides, solvents, and oil spills can be cleaned up with the aid of microbes.

3. Sustaining agriculture

Through their roles in recycling nitrogen, carbon, and sulfur, microorganism are able to convert these essential elements into forms that can be used by plants in their growth. They are also essential in enabling ruminant animals such as cows and sheep to digest cellulose from the grasses they eat.

4. Production of useful natural gene products or products from bioengineering.

Examples include specific enzymes, antibiotics, vaccines, and medications such as human insulin, interferons, and growth hormones.

 

The human microbiota and microbiome: Where we be without microorganisms?

While the typical human body contains an estimated 30 trillion human cells, the vast majority of these being red blood cells, it also contains approximately 39 trillion bacteria and other microbes. The term microbiota (def) is used to desribe the microorganisms that typically inhabit a particular environment, such as the body, the soil, a body of water. Sometimes these microorganisms are also referred to as the microbiome. The number and kinds of microorganisms in and on the body of course varies with age, height, and weight of the individual as well as other factors.  It is estimated the mass of the human microbiota is 2.5 pounds! For example:

• The colon contains an estimated 100,000,000,000 bacteria per milliliter (ml).
• The lower small intestines (illium) contains an estimated 100,000,000 bacteria per ml.
• The upper small intestines (duodenum and jejunum) contains an estimated 1000 - 10,000 bacteria per ml.
• Dental plaque contains an estimated 10,000,000,000 bacteria per ml.
• Saliva contains an estimated 1,000,000,000 bacteria per ml.
• The skin contains an estimated 10,000,000,000 bacteria per square miter of skin with an average adult having 1.8 square miters of skin.

There is a relationship between the the host and its microbiota. Symbiosis (def) is when two dissimilar species or organisms live together. In some cases, the symbiosis is mutualistic (def) where the relationship between the two organisms is mutally beneficial. In other cases it is commensalistic (def) where one organism lives on or within another and derives benefit without necessarily harming or benefiting the host.

It is estimated the the mass of the human microbiota is 2.5 pounds. The complex mutually beneficial symbiotic relationship (def) between humans and their natural microbes is critical to good health. It is now recognized that the millions of genes associated with the microbiota (def) of the human body -especially in the intestinal tract - aid in the digestion of many foods, the regulation of multiple host metabolic pathways, and the regulation the body's immune defenses. These collective microbes and their genes are referred to as the human microbiome (def). There are currently an estimated 5, 000,000 - 10,000,000 genes from over 1000 species that constitute the human microbiome compared to the approximately 20,000 - 23,000 genes that make up the human genome. There are approximately 300 non-human genes in the human body for every human gene.

a. Regulation of Host Metabolism

The mutually beneficial interaction between the human host and its resident microbiota is essential to human health. Microbial genes produce metabolites essential to the host while human genes contribute to development of the microbiota. The microbiome aids in the following:

1. The digestion of many foods, especially plant polysaccharides that would normally be indigestible by humans.

2. The regulation of many host metabolic pathways. The metabolism of many substrates in the human body is carried out by a combination of genes from both the microbiome and the human genome. Within the intestinal tract there is constant chemical communication not only between microbial species but also between microbial cells and human cells. Multiple factors, including diet, antibiotic use, disease, life style, and a person's environment can alter the composition of the microbiota within the gastrointestinal tract and, as a result, influence host biochemistry and the body's susceptibility to disease.

3. Metabolic disorders such as diabetes, nonalcoholic fatty liver disease, hypertension, obesity, gastric ulcers, colon cancer, and possibly some mood and behavior changes through hormone signaling have been linked to alterations in the microbiota.

b. Regulation of Immunity

There is ever growing evidence that symbiotic bacteria (def) of the gastrointestinal tract, as well as parasitic gastrointestinal helminths, may have coevolved with the human body over the past 200,000 year in such a way that genes from the human microbiota may play a significant role in regulating the human immune responses by providing a series of checks and balances that prevent the immune system from being too aggressive and causing an autoimmune attack upon the body's own cells, while still remaining aggressive enough to recognize and remove harmful pathogens. The microbiota affects the development of the immune system while the immune system influences the composition of the microbiota.

As exposure to and colonization with these once common human organisms has drastically changed over time as a result of less exposure to mud, animal and human feces,and helminth ova, coupled with ever increasing antibiotic use that destroys normal flora, improved sanitation, changes in the human diet, increased rate of cesarean sections,decreased rate of breast feeding, and improved methods of processing and preserving of food, the rates of allergies, allergic asthma, and autoimmune diseases (inflammatory bowel disease, Crone's disease, irritable bowel syndrome, type-1 and type-2 diabetes, and multiple sclerosis for example) have dramatically increased in developed countries while remaining relatively low in undeveloped and more agrarian parts of the world.

 

 

Assignment for the next Lecture Period: Flipped-class assignment Read and study the following section under I. Introduction: B. Cellular Organization: Prokaryotic and Eukaryotic Cells in your E-text and answer the 3 learning objectives for this section. We will be doing a classroom group activity on this section so it is critical that you come prepared. I will be assuming that you have done this preparatory assignment.