Bacteria & Viruses

1. Bacteria & Viruses

2. By the end of this class you should understand: • How life may have arisen from nonliving materials • Modern classifications of bacteria and familiar species we encounter every day • The life cycle of parasitic protists • How viruses work and whether they are alive • How to protect yourself from bacteria and viruses

3. Early Life on Earth • Life first appeared around 3.8 billion years ago, soon after liquid water formed • Not recognizable as modern life • Fulfilled the basics of life • Reproduced • Took in energy • Probably didn’t maintain homeostasis very well yet

4. Nonliving Synthesis • Life is formed from large assemblies of macromolecules • How could these have been assembled without life? • There are a number of hypotheses on how these molecules could have been assembled • Clay deposits that preferentially collect charged particles and then dried up • Hydrothermal vents at the ocean floor naturally produce carbon molecules

5. Protocells • One way or another, these molecules eventually formed into protocells • Protocells have been studied as a likely mechanism for a precursor to life • Essentially, fatty acids collect into a simple membrane, and inside, enzymes made of RNA called ribozymes convert other molecules into RNA • Cell grows as more RNA is absorbed and splits naturally

6. Evidence for Protocells • A lot of evidence exists that this mechanism is possible, but that’s not the same thing as evidence that it actually happened • The key evidence is protein synthesis • Common to all life • Uses RNA-based process (ribosomes and tRNA)

7. Prokaryotes Revisited • Modern bacteria are nothing like early bacteria • Through natural selection, only the hardiest and fastest-reproducing bacteria were represented in the next generation • Bacteria can ideally reproduce in 20 minutes • One bacterium in a soup of nutrients can make a colony of 100 million bacteria in 12 hours

8. Three Modern Domains of Life • Archaea • Bacteria that resemble early life • Live in unusual environments • Eubacteria • What we think of as bacteria • All pathogens are eubacteria • Eukarya • All eukaryotes including humans

9. Archaea • Oldest and least changed bacteria • Many live in hostile environments • Extremely acidic • Deep ocean vents • Boiling hot springs (extreme thermophiles) • Salt marshes (extreme halophiles) • Oil wells • Others live in more “normal” environments

10. Eubacteria • Most bacteria that we are familiar with • Many are harmless or even helpful • Bacteria that live on our skin and in our gut are called normal flora and they crowd out more dangerous bacteria • Some are dangerous to our health • Usually eat our tissues for nutrients • Some release dangerous toxins instead

11. Classifications of Eubacteria • Gram staining • Gram positive: turn purple in a Gram stain • Has a cell membrane and a crunchy cell wall • Gram negative: stay pink in a Gram stain • Has two cell membranes with a wall between

12. Another Classification • Aerobic • Aerobic bacteria can survive in air • Many bacteria on the skin • Mitochondria are related to early aerobic bacteria • Anaerobic bacteria • Die when exposed to air • Lack catalase and peroxidase enzymes • Many bacteria in your gut and that spoil food

13. How do anaerobes get around? • Solution: spores! • Some bacteria create spores in harsh conditions • These spores can survive almost anything • Turn back into bacteria when the conditions have improved

14. Bacteria shapes • Coccus – sphere • Bacillus – rod • Spirillum – spiral • Many other weirder shapes also exist • Often in the bacteria name

15. Staphylococcus • Gram positive • Common on human skin, usually harmless • Some are harmful • Infections • Food poisoning • Responsible for “Staph infection”

16. Streptococcus • Gram positive • Many also found on human skin • Dangerous strains responsible for “strep throat” • Even more dangerous types cause Scarlet fever • Most dangerous is “flesh-eating” bacteria • Pictures not provided for the faint of stomach

17. Escherichia coli • “E. coli” • Gram negative • Common in human digestive tract • Helpful for metabolism • Some virulent strains exist • “E. coli” outbreaks are really “Rare and dangerous strain of mutated E. coli outbreak” • Often not the bacteria that is harmful but the toxins it produces

18. Salmonella • Gram negative • Commonly found in humans and farm animals • Can cause food poisoning in undercooked poultry products • Other species cause typhoid fever • Infect human cells using a capsule • Potentially lethal

19. Antibiotics • Antibiotics are chemicals that selectively kill bacteria and not eukaryotic cells • Ineffective against human, yeast, and protozoa • Effective against certain types of bacteria only • Penicillin was the first antibiotic that killed all Gram-positive bacteria • Ampicillin and Streptomycin kill all bacteria

20. Antibiotic resistance • Bacteria constantly mutate and develop new genes • Bacteria also pass genes to each other on plasmids, small rings of DNA • As a result, bacteria may develop a resistance to an antibiotic, so taking antibiotics regularly is generally inadvisable • Additionally, antibiotics kill the normal flora of your intestines and possibly your skin

21. Better the devil you know... • MRSA (methicillin-resistant Staph aureus) is very dangerous • Can have many resistance plasmids • Becoming increasingly common in hospitals • Best defense is a healthy immune system and normal flora

22. This is a real problem…

23. Protists • Protists are eukaryotic single-celled organisms • Amoebas, paramecium, etc. • Many probably resemble early eukaryotes • I will not be covering most of the protists since there are approximately a hojillion of them, but I will cover Plasmodium, the protist that causes malaria • Because I’m friendly like that! • Most protists are NOT infectious

24. Malaria Life Cycle

25. Virus • A virus is a nonliving infectious particle that uses genetic information to reproduce • All viruses reproduce by injecting their genetic molecules into a host cell • The genetic molecules (DNA or RNA) force the cell to make more viruses • Viruses have no metabolism of their own and do not maintain homeostasis or reproduce independently

26. Parts of a Virus • All viruses have: • Protein coat • Spikes that target host cell • Genetic material • Some viruses have a membrane called an envelope

27. What about these weirdos? • This is a bacteriophage • Virus that infects bacteria • Useful in scientific research • Keeps its DNA in the capsule, injects it through the tube into the bacteria • Bacteria have enzymes that try to chop up DNA that doesn’t belong, so it’s an ongoing arms race!

28. What does the genetic info do? • Sample: HIV in human cell • Essentially the DNA or RNA causes the cell to make more viral proteins • The viruses are exocytosed or bud off with envelope until the cell dies

29. Host specificity • The virus spikes can only latch onto certain receptors • This keeps viruses from freely moving between different species of animals • Crossover occurs due to mutation, e.g. “bird flu” • Viruses can only infect certain cells in the host • HIV only infects Helper T cells • Rhinovirus infects epithelial cells • Some viruses (e.g. herpes) infect nerve cells • These are generally incurable

30. Antibiotics NOT for Viruses • Do NOT take antibiotics for viruses • Not only will it do nothing, it exposes you to potential bacterial infections to go with your viral infection! • Vaccines are available for some viruses • A vaccine is a piece of a bacterium or virus that your immune system “learns” to kill • Pre-training your immune system so you don’t get the same disease again • Many viruses and some bacteria mutate too quickly to have effective vaccines made!

31. Protip: • VACCINES DO NOT CAUSE AUTISM • There was a time when vaccines were packaged with an antiseptic called thimerosal, which is a mercury-containing compound • They are no longer packaged as such • The original study linking vaccines and autism was discredited, and many scientists have repeated the experiment but found no statistically significant difference • Autism is a developmental disorder and more prevalent in males, it cannot be caused by an injection at six months of age

32. See you in lab!