Prokaryotes Biology

What are Prokaryotes? Single-celled organisms Very tiny Cannot be seen without a microscope Our microscopes are not powerful enough Lack a nucleus and most other organelles Most numerous organisms on Earth Extremely important organisms.

Classification and Evolution Prokaryotes are split into 2 Domains Domain Bacteria Domain Archaea Everything else on Earth is in Domain Eukarya Prokaryotes were the first living things to evolve, around 3.8 billion years ago Only living things on earth until 2 billion years ago Until 1970s, Archaea were considered to be bacteria (called Archaebacteria) As more was learned about them, they were given their own domain because they are VERY different from bacteria

Domain Bacteria Made up of bacteria Only 1 kingdom-Bacteria Most abundant living things on Earth. Live in almost every environment Air Ocean Soil Intestines Estimated number of bacteria on earth: 5x1030 You have 10 times more bacterial cells than human cells!

Classification of Bacteria Thousands of bacterial species exist. Many are classified by shape. Others are classified based on the color that they stain (Gram staining)

Bacterial shapes Baccili: Cocci: Spirilla Rod shaped Sphere-shaped Spiral-shaped

Structure of Bacterial Cells Bacterial cells are surrounded by a plasma membrane Most also have cell walls Surrounding the membranes and cell wall (if present) is a capsule, which further protects the cells Inside of the bacterial cell is cytoplasm, similar to eukaryotic cells Floating in the cytoplasm are ribosomes and plasmids (small sections of DNA) There is no nucleus Instead, there is a Nucleoid (area with DNA) and may be plasmids (circular DNA) to be exchanged with other bacteria Bacterial cells also may contain whip-like structures called flagella Also have hair-like protrusions called pili that allow them to attach to objects

Structure of Bacterial Cells

How do bacteria get energy? Some are photosynthetic Others decompose organic matter Some can use chemicals from the environment to do a process similar to photosynthesis (called chemosynthesis) Mutualism Getting resources from other species, while providing some service to that species (+/+) Parasitism Stealing resources from host organisms (+/-)

Bacteria and People You may think that bacteria’s purpose is to make us sick For some bacteria, this is true For many others, it is not Benefits of Bacteria Create medicine, such as vaccines Help us digest foods and get vitamins Decompose wastes Fix Nitrogen into usable forms for plants Make foods such as cottage cheese, yogurt, cheese, and many more.

Dark side of Bacteria Some bacteria can lead to disease Clostridium tetani Tetanus aka Lockjaw Affects muscles (including the heart). Leads to muscle spasms, and can be fatal. Escherichia coli (E. Coli) Many strains exist in human intestines in a commensalism relationship. However, some can cause food poisoning. Transmitted by fecal-oral route. WASH YOUR HANDS AFTER USING THE BATHROOM!!! Salmonella bongori & Salmonella enterica Salmonella Cause Typhoid fever (very fatal) and Food Poisoning

Dark side of Bacteria Continued Staphylococcus (many species) Sinus infections, ear infections, skin infections, food poisoning Streptococcus (Many species) Pneumonia, necrotizing fasciitis (flesh-eating bacteria), pink eye, strep throat Mycobacterium tuberculosis (Tuberculosis) Second deadliest infectious disease (After HIV/AIDS). Yersinia pestis “The Bubonic Plague” or “The Black Death Killed over 1/3 of the European Population between 1347 and 1353

A child and a portrait of a soldier affected with tetanus

If you have a weak stomach, please look away now…

Spread of the Black Death

Artist drawing of a typical street during the spread of the black death.

At least the Plague is over… Right?

Controlling Bacteria Bacteria in food and water can be killed by cooking at a high temperature Bacteria on surfaces can be killed with cleaning products such as bleach or Lysol Antibiotics can be used to kill bacteria that are harming humans Effective against bacterial infections such as strep throat, sinus infections, ear infections, pneumonia, etc. However, there is a problem

Antibiotic Resistance in Bacteria Some bacterial species are evolving resistance to antibiotics. https://www.youtube.com/watch?v=znnp-Ivj2ek The antibiotic kills those that are not resistant, but leaves the one that are resistant Example: Clostridium difficile A common bacteria that causes diarrheal disease in hospitals. Hospitals, due to their obsessive cleaning procedures, have selected for resistant strains. Patients are being infected at a high rate, while staying in hospitals.

Even more alarming… Remember how we just learned that Tuberculosis is the 2nd most deadly infectious disease… Well… Tuberculosis is spreading due to becoming resistant to the antibiotics typically used to treat it. One strain is totally resistant to ALL drugs currently used Another is resistant to 3 of the 6 drugs used to treat it.

Genetic Diversity in Bacteria Bacteria reproduce asexually (without sex) Called binary fission One bacteria replicates its DNA and then splits Makes clones-identical copies Benefit: Quick, little energy used, don’t need a mate Disadvantage: No genetic diversity Susceptible to extinction Conjugation is a way bacteria can increase genetic diversity Exchanging all or part of a plasmid with another bacteria No longer identical

Antibiotic Resistance and Evolution by Natural Selection Organisms must adapt to changing environments or they will die off Called natural selection As organisms adapt, the frequency of alleles (traits) in the population change Evolution Bacteria, because they reproduce asexually, are able to quickly adapt The antibiotic kills the weak ones and eliminates them as competition for strong ones. They will rapidly reproduce

Domain Archaea Only 1 Kingdom Prokaryotes Called Archaea (Surprised?) Prokaryotes First discovered in extreme environments Originally classified as bacteria As more was learned about them, they were found to be VERY different from bacteria Their cell wall is more similar to Eukaryotes than bacteria They were given their own Domain and Kingdom Very little is known about these organisms

Archaea: Tiny but Tough Many archaea are extremophiles Organisms that have evolved to live in extreme conditions. Example: Hydrothermal vents in the ocean (picture) are very acidic and hot. Would kill most organisms, yet archaea thrive. 4 types of extremophiles Halophiles-Survive in very salty water (Dead sea) Hyperthermophiles- Survive at high heats Some archaea can survive up to 122° C (252° F) Acidophiles-Live in highly acidic environments (like near volcanoes) Alkaliphiles-Live in very basic environments

Where else do they live? Archaea do not only live in extreme environments They are found nearly everywhere on Earth. Including in humans (many are found in the human belly button!) Around 4 % of human microbiome The microorganisms that live on or in us They are also important decomposers, and part of Nitrogen cycle Many archaea also form symbiotic relationships None are known parasites Most form mutualistic relationships Archaea in cattle gut help break down grass and straw, and get nutrients in return