Let's start by continuing with our discussion of history which..... will lead us into the next topic....evolutionary history and classification of microorganisms

Let's go a little bit into the modern era. In 1922 A.J. Kluyver replaced Beijerinck at the University of Delft and ushered in the modern era of comparative biochemistry. Kluyver and his student C.B. van Niel proposed that all respiratory reactions (aerobic and anaerobic) could be summarized using the simple formula:

They also summarized all photosynthetic reactions with:

We will come back to these reactions in a few weeks.

And now for some history of medical microbiology.
Disease-causing microorganisms have played a major role in the outcomes of history - leading to the downfall of empires and the defeat of large armies. This was especially true prior to World War II - because in earlier wars soldiers usually lived in close quarters under unsanitary conditions where disease could spread rapidily. Many historians think that diseases and infections have killed far more soldiers than actual battles over the ages. We will discuss the historical implications of diseases when we talk about specific diseases later in the course (for now be sure and read pgs. 28-30).

Some Famous Names in Medical Microbiology:

R. Koch (1843-1910)

Koch was a country doctor who was given a microscope by his wife. He was looking at the blood of an ox that had died of anthrax and noticed that, besides blood cells, there were a lot of little stick-like things in the fluid (he never saw these sticks in blood from healthy animals). He later grew these sticks in some fluid from the eye of an ox and then injected them into a mouse and the mouse died of anthrax. When he looked at the blood of the dead mouse he again saw the sticks and he was able to culture the sticks from the mouse's blood. This was the first clear experimental evidence showing that a bacterium can cause a disease. This early experiment and many later ones led to what we now call Koch's postulates. Koch's postulates are a set of rules to prove that a specific organism causes a specific disease...........

Koch's Postulates:

1) A specific microorganism is always present in organisms (hosts) with a specific disease.

2) The organism must be cultured away from the host.

3) Inoculation of a new host must lead to the same disease

4) The microbes must be re-cultured from the inoculated host.

See overhead.....

Koch also determined that the organism that causes anthrax (now called Bacillus anthracis) had a life cycle that included a very resistant spore (endospore) that could survive for years in soil.

Koch went on to study other diseases and many of his students and colleagues made important discoveries in microbiology. Table 2.1 shows some of the diseases that were figured out by Koch and others in the late 1800s.

Koch's lab was also the birth place of pure culture microbiology, especially after Fannie Hesse discovered that agar could be used as a solidifying agent for bacteriological media in 1882.

Another of Koch's co-workers, Paul Ehrlich, is credited as being the discoverer of chemotherapy. Ehrlich noticed that bacteria picked up certain stains more readily than did mammalian tissue. This led him to believe that microbes might also be more susceptible to certain toxins than humans. His first success was with an arsenic-containing compound (Salvarsan) that killed Trypanosomes and the bacterium that causes syphilis (Treponema pallidum). These early chemo-therapeutic agents sometimes had nasty side effects. It wasn't until the mid-1900s that very specific antibiotics were developed (more about that later).

Lec. 3 (cont.)

Our next goal is to gain a broad understanding of the diversity and classification of microorganisms. We will learn the major groups of Bacteria, Archaea and Eukaryotic microbes so that as the course goes on we can place all of the microbes that we talk about into these groups.

Let's start by thinking about the relationship between evolution and classification. It is the goal of systematic biologists to develop classification schemes that reflect true (evolutionary) relatedness among organisms. Such phylogenetic systems not only make organizing all of life a lot easier but they also can have profound practical implications. For example, if you discovered a new bacterium, wouldn't you want to know if it were closely related to a deadly pathogen?

One big problem with microbial systematics is that many microbes (especially bacteria) look alike. We will discuss the biophysical reasons for this next week but for now just believe me that one rod-shaped bacterium looks pretty much like another under the microscope! With this in mind, let's take a brief journey through the history of microbial systematics.

A little after the time of Leeuwenhoek (see lec. 2), a botanist named Linnaeus was attempting to classify all living things. In his 1759 treatise he divided the world into Animal, Vegetable and Mineral and named all organisms that he knew of using the binomial (Genus species) system that we still use today. Obviously not much was known about microbes at that time so Linnaeus gave up in frustration and put all microscopic life into one genus, Chaos!

In the next 100 years enough progress had been made in microbiology so that E. Haeckel at least gave microbes some credit....show 1866 tree (Plants, Animals and Protists=bacteria, fungi, protozoa).

As long as we're taking 100 year leaps, let's go to 1969 when Whittaker and others introduced the 5 kingdom system for classifying all life (Plants, Animals, Fungi, Protists and Bacteria). This system was based mostly on the 3 main modes of nutrition: photosynthesis, absorption, and ingestion...... draw foot tree. This tree of life has been widely accepted but it is no longer believed to be phylogenetically correct. The most offensive aspect of this tree is that it implies that all prokaryotes are all closely related to one another (simply because they are small and have simple morphologies) and it also implies that microbes are primitive and haven't been evolving along with everybody else......

Fortunately, there has been a great deal of progress in the last 20 years in classifying microorganisms. Microbiologists have long known that the morphology of a bacterium is not a good character to use in classifying them. The most progress has been made using methods that compare the sequences of bases in DNA or the sequence of monomers in macromolecules coded for by DNA. Many such molecules have been tested in this regard and a few are now used to classify microbes. Perhaps the most useful sequences have been those of rRNA. This molecule occurs in all forms of life and different parts of it's sequence are thought to have changed at different rates over evolutionary time.

For classifying bacteria we usually compare the sequence of the 16S region of the ribosome of an unknown critter with a data base of sequences from known organisms. Most of the classification scheme given in your book is based on 16S sequences (or 18S in Eukaryotes). There are also well established diagnostic tests for identifying many bacteria. These tests have largely confirmed much of the phylogenetic scheme we will discuss in this class. You will also get to use some of these commonly used diagnostic tests in the laboratory part of this course.

Before we get down to specific groups of microbes let's see what sort of tree that sequencing gives for all of life on earth....

Show tree

3 domains of life:

Bacteria = Eubacteria (see lectures 5 and 6)

Archaea (sometimes called "Archaebacteria")

Eucarya = Eukaryotes (including the fungi, protozoa etc.)

Please read the interview with Carl Woese (pp. 384-387).

Link to more information on the tree of life.

Point out some of the major groups of organisms.............