Microbial Life: Origin and Discovery – Chapter 1 Study Notes

Microbial Life: Origin and Discovery

Introduction to Microbiology

Microbiology is the study of microscopic organisms, known as microbes, which include bacteria, archaea, fungi, protozoa, algae, and viruses. Microbes are fundamental to life on Earth and have played a significant role in shaping human history, the development of medical science, and the natural environment.

• Microbes are found everywhere and are incredibly abundant and diverse.

• A vast realm of biodiversity resides in Earth's oceans and soils.

• The human body contains as many microbes as human cells, forming complex communities.

What Is a Microbe?

Definition and Characteristics

A microbe is a microscopic organism that cannot be seen with the unaided eye. Most microbes consist of a single cell, but some are multicellular. They vary greatly in size and structure.

• Size range: Microbes range from 0.2 μm to 5 mm.

• Viruses are ten times smaller than the smallest cells and are considered acellular entities.

• Each microbe contains a genome used to reproduce its own kind.

Types of Microbes

Microbes include both prokaryotic and eukaryotic organisms, as well as acellular viruses.

• Prokaryotes: Cells lacking a nucleus, such as bacteria and archaea.

• Eukaryotes: Cells with a nucleus, including algae, fungi, and protozoa.

• Viruses: Acellular entities that require host cells for replication.

All living organisms are classified into three domains: Bacteria, Archaea, and Eukarya, which evolved from a common ancestral cell.

Microbial Diversity and Abundance

Microbes in the Environment

Microbes are the most abundant life forms on Earth and have dominated the planet for billions of years. Their diversity is vast, and much of it remains a mystery.

• Photosynthetic Prochlorococcus bacteria are tiny cells that produce the oxygen gas we breathe.

• Microbes play essential roles in nutrient cycling, decomposition, and supporting ecosystems.

Classification of Microbes

Domains of Life

Microbes are present in all three domains of life:

• Bacteria: Prokaryotic, single-celled organisms found in diverse environments.

• Archaea: Prokaryotic, often extremophilic organisms distinct from bacteria.

• Eukarya: Includes algae, fungi, protozoa, plants, and animals.

These domains reflect evolutionary relationships and fundamental differences in cellular structure and genetics.

Key Terms and Concepts

• Microbe: A microscopic organism, including bacteria, archaea, fungi, protozoa, algae, and viruses.

• Prokaryote: An organism whose cells lack a nucleus (e.g., bacteria, archaea).

• Eukaryote: An organism whose cells contain a nucleus (e.g., algae, fungi, protozoa).

• Virus: An acellular infectious agent that requires a host cell for replication.

• Genome: The complete set of genetic material in an organism.

Table: Comparison of Microbial Types

Type	Cell Structure	Examples	Domain
Bacteria	Prokaryotic (no nucleus)	Escherichia coli, Staphylococcus aureus	Bacteria
Archaea	Prokaryotic (no nucleus)	Halobacterium, Methanogens	Archaea
Eukaryotes	Eukaryotic (nucleus present)	Yeast, Amoeba, Algae	Eukarya
Viruses	Acellular	Influenza virus, HIV	None (not classified as living)

Important Equations

• Size Range of Microbes:

$0.2\ \mu m \leq \text{Microbe Size} \leq 5\ mm$

Summary

Microbes are microscopic organisms that include bacteria, archaea, eukaryotes, and viruses. They are essential to life on Earth, contributing to biodiversity, ecosystem function, and human health. Understanding their classification, diversity, and roles is fundamental to the study of microbiology.