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(From Horton Hears a Who, Dr. Seuss)

On the fifteenth of May, in the jungle of Nool,
In the heat of the day, in the cool of the pool,
He was splashing…enjoying the jungle’s great joys…
When Horton the elephant heard a small noise.

So Horton stopped splashing. He looked towards the sound.
“That’s funny,” thought Horton. “There’s no one around.”
Then he heard it again! Just a very faint yelp
As if some tiny person were calling for help.
“I’ll help you,” said Horton. “But who are you? Where?”
He looked and he looked. He could see nothing there
But a small speck of dust blowing past though the air.

“I say!” murmured Horton. “I’ve never heard tell
Of a small speck of dust that is able to yell.
So you know what I think?…Why, I think that there must
Be someone on top of that small speck of dust!
Some sort of a creature of very small size,
too small to be seen by an elephant’s eyes…

In this well-known children's story, Horton the Elephant discovers that a tiny speck of dust contains an entire world of creatures much too small for him to see. Well, it turns out that EVERY speck of dust, every drop of water, every grain of soil, and every part of every plant and animal around us contain their own worlds of microbial inhabitants.

A very tiny fraction of these creatures can do us harm, causing misery, disease and death, and these few creatures have given the microbial world a bad reputation. But the vast majority of microbes benefit us in essential ways that we fail to recognize. They created, and sustain, the world we live in. The famous paleontologist and evolutionary biologist Stephen J Gould once wrote, "On any possible, reasonable, or fair criterion, bacteria are - and always have been - the dominant forms of life on Earth.".

Welcome to Microbiology 451, Microbial Diversity. In this course, we will explore, a little bit, the enormous range of biological diversity in the microbial world.

In the first section of this course, we'll establish a point of view from which to examine microbial diversity - call this the "phylogenetic perspective". This will be primarily a problem-solving section of the course, in which we'll learn how to construct and interpret evolutionary trees from DNA sequences. We'll finish up with a look at the universal "Tree of Life" constructed using this process.

In the second section of this course, we'll climb around in this "tree of life", looking at some examples of microbes on the major branches of the tree - sort of a stroll through the microbial zoo. We'll extract some conceptual lessons from each group, but this section of the course will be mostly about establishing a base of knowledge about the microbial world.

In the third (and last) section of the course, we'll learn about how microbiologists are beginning to explore the universe of microbial diversity "in the wild". We'll do this directly from published research papers, starting with how new organisms are identified (usually without being cultivated), and progressing in steps to broad surveys of entire microbial communities, and attempts to get a handle on how specific kinds of organisms contribute to the ecosystem. This is the conceptual and synthetic portion of the course.

In the end, I hope you will have gained an appreciation for the "big picture" of the microbial world, an understanding of the power of the phylogenetic perspective, and a realization that the exploration of this world is just beginning, how this is being done, and the questions that drive this exploration.

We live immersed in an infinite sea of the infinitesimal. Let's have a look.