lecture 1

Microbiology

Microbiology

The study of microorganisms, including bacteria, viruses, fungi, and protozoa.

Carl Woese

Scientist known for establishing the three-domain system for classifying cellular life.

Prokaryotic cells

Cells that lack a true membrane-delimited nucleus.

Domain Bacteria

One of the three domains of life, characterized by single-celled organisms with cell walls containing peptidoglycan.

Domain Archaea

Another domain of life distinguished by unique rRNA gene sequences and the absence of peptidoglycan in cell walls.

Domain Eukarya

The domain that includes eukaryotic organisms such as protists, fungi, plants, and animals.

Viruses

Acellular infectious agents that require a host cell to replicate.

Ribosomal RNA (rRNA)

RNA molecules essential for protein synthesis and used in classification schemes to categorize microorganisms.

Last Universal Common Ancestor (LUCA)

The hypothetical organism from which all life on Earth is descended.

Horizontal gene transfer

The transfer of genetic material between organisms in the same generation, contributing to genetic diversity in bacteria and archaea.

Microbiology

The study of microorganisms.

Antony van Leeuwenhoek

The first person to observe and describe microorganisms accurately.

Spontaneous generation

The idea that living organisms can develop from nonliving or decomposing matter.

Louis Pasteur

Conducted 'Swan-neck flask' experiments to disprove spontaneous generation and showed that microorganisms did not grow in boiled solutions left exposed to air.

John Tyndall

Demonstrated that dust carries microorganisms and provided evidence for the existence of exceptionally heat-resistant forms of bacteria.

Ferdinand Cohn

Showed that heat-resistant bacteria could produce endospores.

Robert Koch

Established the relationship between Bacillus anthracis and anthrax, developing Koch's postulates to link a microorganism to a specific disease.

Koch’s Postulates

A set of criteria used to establish a causative relationship between a microorganism and a disease.

Agar

A gel-like substance derived from seaweed, used as a growth medium for microorganisms.

Petri dishes

Flat, round dishes with a cover used to culture microorganisms.

Charles Chamberland

A scientist who developed porcelain bacterial filters used in studying infectious agents.

Attenuation

The process by which pathogens lose their ability to cause disease after prolonged incubation.

Edward Jenner

A scientist who pioneered the use of vaccination to protect individuals from smallpox.

Antitoxins

Substances developed by scientists like Emil von Behring and Shibasaburo Kitasato to counteract toxins produced by pathogens.

Louis Pasteur

Scientist known for demonstrating the role of microbes in fermentation and developing pasteurization.

Sergei Winogradsky and Martinus Beijerinck

Scientists who studied soil microorganisms and their metabolic processes.

Molecular Biology

The study of genetic information and its regulation in

The Importance of Microorganisms

• Most populous and diverse group of organisms

• Found everywhere on the planet

• Play a major role in recycling essential elements

• Source of nutrients and some carry out photosynthesis

• Benefit society by their production of food, beverages, antibiotics, and vitamins

• Some cause disease in plants and animals

Members of the Microbial World

• Organisms and acellular entities too small to be clearly seen by the unaided eye – some < 1 mm, some macroscopic

• These organisms are relatively simple in their construction and lack highly differentiated cells and distinct tissues

Type of Microbial Cells

• Prokaryotic cells lack a true membrane-delimited nucleus – this is not absolute!

• Eukaryotic cells have a membrane-enclosed nucleus, are more complex morphologically, and are usually larger than prokaryotic cells

Classification Schemes

• Three domain system, based on a comparison of ribosomal RNA genes, divides microorganisms into – Bacteria (true bacteria),– Archaea– Eukarya (eukaryotes)

Domain Bacteria

• Usually single-celled

• Majority have cell wall with peptidoglycan

• Most lack a membrane-bound nucleus

• Ubiquitous and some live in extreme environments

• Cyanobacteria produce significant amounts of oxygen

Domain Archaea

• Distinguished from Bacteria by unique rRNA gene sequences

• Lack peptidoglycan in cell walls

• Have unique membrane lipids

• Some have unusual metabolic characteristics

• Many live in extreme environments

Domain Eukarya - Eukaryotic

1. Protists – generally larger than Bacteria and Archaea

   • algae – photosynthetic

   • protozoa – may be motile, “hunters, grazers”

   • slime molds – two life cycle stages

   • water molds – devastating disease in plants

2. Fungi

   • yeast - unicellular

   • mold - multicellular

Acellular Infectious Agents

1. Viruses

   • smallest of all microbes

   • requires host cell to replicate

   • cause range of diseases, some cancers

2. Viroids and virusoids

   • infectious agents composed of RNA

3. Prions – infectious proteins

Microbial Evolution

• Definition of life

  • cells and organization

  • response to environmental changes

  • growth and development

  • biological evolution

  • energy use and metabolism

  • regulation and homeostasis

  • reproduction

Origins of Life

1. Microbial fossils

   • Swartkoppie chert – granular silica

   • 3.5 billion years old

2. Fossil record sparse

3. Indirect evidence and scientific method are used to study origins of life

Earliest Molecules - RNA

1. Original molecule must have fulfilled protein and hereditary function

2. Ribozymes

   • RNA molecules that form peptide bonds

   • perform cellular work and replication

3. Earliest cells may have been RNA surrounded by liposomes

4. Cellular pool of RNA in modern day cells exists in and is associated with the ribosome (rRNA, tRNA, mRNA)

   • RNA catalytic in protein synthesis

   • RNA may be precursor to double stranded DNA

5. Adenosine 5’ triphosphate (ATP) is the energy currency and is a ribonucleotide

6. RNA can regulate gene expression

Earliest Metabolism

1. Early energy sources under harsh conditions

   • inorganics, e.g., FeS

2. Photosynthesis

   • cyanobacteria evolved 2.5 billion years ago

   • stromatolites

   • mineralized layers of microorganisms

Evolution of 3 Domains of Life

Universal phylogenetic tree

• based on comparisons of small subunit rRNA (SSU rRNA)

• aligned rRNA sequences from diverse organisms are compared and differences counted to derive a value of evolutionary distance

• relatedness, but not time of divergence, is determined this way

Last Universal Common Ancestor (LUCA)

• The root or origin of modern life is on bacterial branch but nature still controversial

• Archaea and Eukarya evolved independently of Bacteria

• Archaea and Eukarya diverged from common ancestry

Endosymbiotic Hypothesis

1. Origin of mitochondria, chloroplasts, and hydrogenosomes from endosymbiont

2. Mitochondria and chloroplasts

   • SSU rRNA genes show bacterial lineage

   • genome sequences closely related to Rickettsia and Prochloron, respectively

3. Hydrogenosomes

   • anaerobic endosymbiont

Evolution of Cellular Microbes

• Mutation of genetic material led to selected traits

• New genes and genotypes evolved

• Bacteria and Archaea increase genetic pool by horizontal gene transfer within the same generation

Microbial Species

1. Eukaryotic microbes fit definition of reproducing isolated populations

2. Bacteria and Archaea do not reproduce sexually and are referred to as strains

   • a strain consists of descendents of a single, pure microbial culture

   • may be biovars, serovars, morphovars, pathovars

3. binomial nomenclature– genus and species epithet

Limitations of Koch’s Postulates

• Some organisms cannot be grown in pure culture

• Using humans in completing the postulates is unethical

• Molecular and genetic evidence may replace and overcome these limits