Lec 5
Introduction to SARS CoV-2 and Vibrio Cholera
Discussion of the evolution and transmission speed of pathogens including
SARS CoV-2, responsible for COVID-19
Infection of various nonhuman animal species
Vibrio cholera, the bacterium that causes cholera
Interest in environmental bacteria and their responses to pesticides
Focus on predicting and preventing harmful cyanobacterial blooms and other environmental disturbances.
Overview of Lecture Structure
Each lecture will utilize a phylogenetic tree for orientation.
Focus areas for this session include:
Study of bacteria, archaea, and some eukaryotic microbes.
Species Estimates
Estimated 8,700,000 eukaryotic species worldwide.
Audience engagement: Estimation of microbial species:
Responses ranged from 100,000,000 to 20,000,000,000.
Current estimates suggest around a trillion (i.e., ) microbial species exist, a debated figure.
Importance of Microbes
Microbes have significant impacts on health and the environment:
Can act as pathogens (harmful bacteria and viruses).
Contribute positively (i.e., gut microbiome aiding digestion, immune training).
Evolution of microbes:
Spanning billions of years, filling every ecological niche on Earth.
Essential roles in global nutrient cycles (carbon, nitrogen, phosphorus).
Rapid evolution observed during pandemics.
Learning Objectives
Historical perspective on the germ theory of disease.
Definition and implications of symbiosis in microbe interactions.
Evidence of microbial evolution over ancient and recent timescales.
Development of methods for studying microbes:
From microscopy to modern DNA sequencing.
Levels of biological organization:
Coupling of metabolism and genetic information.
Historical Perspective on Germ Theory of Disease
Louis Pasteur's work in the 1870s:
Showed invisible microbes responsible for fermentation (beer, wine, cheese) and infections.
Investigated the concept of spontaneous generation.
Conducted experiments using flasks to demonstrate:
Open flasks became contaminated.
Sealed flasks remained sterile.
Robert Koch's contributions in the 1890s:
Showed how specific microbes cause disease.
Proposed "Koch's Postulates" to demonstrate causality in infectious diseases:
Isolate the microbe from a diseased organism.
Cultivate the microbe separately and show it causes disease when introduced to a healthy organism.
Re-isolate the same microbe from the newly diseased organism.
Addressed challenges of isolating pathogens in the 1890s.
Definition of Symbiosis
Symbiosis refers to organisms living together, encompassing both beneficial and harmful relationships.
Example: Vibrio fischeri, a beneficial bacterium for bobtail squid, enhancing camouflage.
Note: It's closely related to the pathogen Vibrio cholerae.
Significance of understanding fine lines between pathogens and beneficial symbionts across various hosts (plants, animals, humans).
Human Microbiome
Humans composed of around 2% bacteria by mass, primarily in the gut.
Estimated ratio of bacterial to human cells is around 1:1,
Recent estimates suggest a ratio of about 100 bacterial genes for every single human gene.
Importance of the microbiome includes:
Digestive functions, immune system training, protection against pathogens.
Evidence of Microbial Evolution
Microbial fossil evidence includes stromatolites dating back approximately 3.5 billion years.
Current stromatolites can still be observed in natural habitats (e.g., The Bahamas).
Geochemical evidence is indicated through:
Banded iron formations as indirect evidence of ancient life related to cyanobacteria.
Contemporary Evolution
Laboratory observations of bacterial evolution, such as:
Richard Lenski's E. coli experiment since 1988 involving over 65,000 generations.
Continuous adaptation observed over generations, yielding insights into fitness and evolution.
Microbial Definition
A microbe is defined as an organism that cannot be seen without magnification, including both prokaryotic and eukaryotic organisms.
Advantages of Being Microscopic
Microscopic cells can grow faster due to higher surface area-to-volume ratios.
Allows for better nutrient absorption and efficient replication processes.
Tools for Studying Microbes
Microscopes:
Early simple magnifying glasses and advancements leading to compound microscopes.
Robert Hooke's contributions to microscopy and the discovery of cells.
Antonie van Leeuwenhoek’s observations of bacteria.
DNA Sequencing:
Technological advancements have led to cheaper and faster genome sequencing.
Measures decrease in sequencing costs vs. computer processing capabilities (Moore's Law).
Enables extensive genetic study of both prokaryotic and eukaryotic organisms.
Levels of Biological Organization
Fundamental units include:
Cells: The unit of metabolism and replication.
Populations: Groups of cells evolving together.
Communities: Different species interacting within ecosystems.
Importance of understanding metabolic coupling and genetic information.
Cell Structure
Cells are bounded by plasma membranes, essential for maintaining separate internal environments.
Fundamental processes include:
Metabolism: Generation and harvesting of energy to synthesize new biomass.
Information: Genetic data required for metabolic functions and reproduction.
DNA Replication and Mutation Rates
DNA replication involves complementary base pairing and enzyme functions (DNA polymerase).
Mutation rates are low but significant at population levels, leading to genetic variation.
Bacterial reproduction:
Division of biomass and the replication of information
Bacteria genome has 2 million base pairs and 2000 genes
Formed by a single molecule of DNA
Bacteria has nucleoid and circular bacterial chromosone
Plasmids? Occur in bacteria and are small DNA molecules.
They replicate at the same time as the chromosone — daughter cells don’t always recieve equal numbers
Some plasmids encode conjugation that results in horizontal transfer from donor to recipient via pilus
Plasmids can encode functions beneift to the host, but in many cases they are parasites
DNA replication - double stranded with complementary base pars
DNA will unwind, and synthesis of complimentary strands
Key enzyme — DNA polymerase that match G-C and A-T base pairs, facilitating the formation of new DNA strands during replication.
Occasionally mutations occur
Chromosone replication and cell division are linked
single cell — replicates its DNA and divides bio mass exponentially — mutation and random errors — allows for variation — natural selection — evolution
Photoautotroph - photosynthesis
Heterotroph - Aerboic respiration
Conclusion
Understanding microbial evolution informs broader ecological interactions, exemplified by trophic linkages between phototrophs and heterotrophs (e.g., cyanobacteria and aerobic organisms).
Next class topics will include further exploration into metabolism and origins of life concepts.