chapter 22: prokaryotes - BIOL 2130

prokaryotes

the first known inhabitants of the planet and appeared 3.8 bil years ago

• archaea and bacteria

• single-celled organisms

• no defined nucleus

• lack some other organelles

• inhabit extreme environments

• live on or in virtually every living thing on earth

prokaryote origin

earth approx 4.5 bil years ago had strong solar radiation, anoxic atmosphere, and strong volcanic activity = lots of mutation

• first prokaryotes for anaerobic (no one knows how they arrived since no fossils)

• cyanobacteria appear by 2.5 bil years ago and began oxygenation of the atmosphere: photosynthesis and release O2

• phototrophs appear approx 3.5 bil years ago: harness light for energy

• oxygenation = formation of the ozone layer: protects life from harmful UV radiation

microbial mats

multilayered sheet of prokaryotes, mostly bacterial and some archaeans, and exists everywhere different types of materials meet

• fossil evidence of occurrence back 3.5 bil years ago

• obtained energy from hydrothermal vents until photosynthesis

• few cm thick

• stromatolites: remains of microbial mats that trapped precipitated minerals out of the water

extremophiles

prokaryotes of mostly archaea, and some bacteria, that adapt to survive in harsh environments and cannot survive in moderate environments

• protective cell wall

• exploring extraterrestrial environments

• ex: acidophiles — pH 3 or below

• ex: halophils — salt conc of at least 0.2 M

robert koch

discovered techniques for culturing bacteria (tuberculosis) and created postulates to identify bacteria that can cause disease

1) organism can be identified as a cause of disease when it is present in all infected samples

2) organism able to cause infection after cultured many times

3) only applied to organisms isolated and successfully cultured in a lab

• 99% of bacteria and archaea cannot be grown in a lab setting bc unknown environmental needs

viable but not culturable (VBNC)

cultural organisms become unculturable under stressful conditions as a mechanism for self-preservation

• dormant state (inactive), triggers for this is not well understood

• resuscitation (restoring) occurs when environmental conditions improve: important for pathogen survival and risks with persistence in the environment

biofilms

structured communities of prokaryotes attached to surfaces, self producing extracellular matrix

• prokaryotes prefer to live in communities to interact with each other

• robust populations

• ex: dental plaque on teeth

prokaryotic cell

• unicellular

• lack membrane-bound organelles: nucleus, mitochondria, etc., DNA free in cytoplasm

• nucleoid: one circular strand of DNA

• protective cell wall

• some with capsules to aid in attaching to other cells and avoid desiccation (drying out)

• some with flagella for movement

• asexual reproduction

binary fission

prokaryotes typical method of asexual reproduction

• duplicating chromosome (single circular DNA)

• separating the copies

• enlarged prokaryote splits at middle → 2 identical progeny

• does NOT allow for genetic diversity

prokaryotic diversity

1) transformation: prokaryote takes in DNA shed by another prokaryote in its env, new DNA sequence into its own

• nonpathogenic to pathogenic!

• closely balanced to prevent harm

2) transduction: bacteriophages may move short pieces of DNA from one bacteria to another

• recombinant organism

3) conjugation: DNA transfer via a pilus (tube) for direct contact with each other

pathogen borne disease

illness caused by pathogens such as bacteria, viruses, fungi, or parasites

• affected human populations and ancestors for mils of years

• understood scientifically the last few hundred years

• earlier beliefs: diseases were caused by spiritual ailments

history

bacterial infections record back to 3000 BC in both fossilized remains and written records

• 430 BC plague of athens: thought to be typhoid fever caused by Salmonella enterica

  • killed ¼ of athenian troops in peloponnesian war

  • identified by info from DNA in teeth of dead soldiers

plagues attacked the lymph nodes, showed over and over in european history

• 541 BC plague of justinian: decreased european population by 50%

• 1346 black death: Yersinia pestis decreased world population form 430 mil to 350 mil, struck london again in 1600s

• spread of disease exacerbated by world travel

• 1000-3000 cases each year now, treated w antibiotics

foodborne disease

prokaryotic infection/pathogens and contaminate food in the form of a biofilm

• contamination from food processing equipment or from food itself

• 76 mil ppl get sick a year, likely more who don’t get help

• ex: salmonella spread from not taking care of eggs after popped out

biofilms and disease

biofilms are difficult to destroy because of their antibiotic resistance, and can cause an array of human disease

• ex: otitis media (ear), legionnaire’s disease (water), infections in those with cystic fibrosis (mucus and respiratory)

• can grow on medical devices making it even harder to treat

• 65% of hospital infections are due to biofilms

antibiotics

chemical produced either by an organism or synthetically that prevents the growth of another organism

• less than 1% of prokaryotes are pathogenic: either beneficial or harmless!

• exploit competition to protect human and animals from pathogenic bacteria!

nitrogen cycle

how nitrogen is fixed into an accessible form

• nitrogen: essential for nucleic acids and proteins for the building blocks of life

• largest in the atmosphere as N2, inaccessible to most organisms

• bacteria → denitrifying bacteria, nitrogen gas, nitrates (green plants, animals, fish waste), ammonia

1) abiotic fixation: industrial production for fertilizers

2) biological nitrogen fixation: prokaryotes convert to ammonia or other usable forms

• ex: cyanobacteria in aquatic env

• ex: rhizobia in soil env

• ex: symbiotic fixation — legumes, cheap fertilizer, ammonia, crucial agriculture protein

  • legumes: rhizobia bacteria in root nodules convert N2 to ammonia for the legume plant

• THE MOST IMPORTANT NATURAL CYCLE: accounts for 65% of nitrogen used in agriculture (crop growth and food production)

carbon cycle

movement of carbon in atmosphere, oceans, biosphere, geosphere

• when decomposers break down decaying organic matter and release carbon dioxide through cellular respiration

• photosynthesis: take in CO2 from atmosphere into sugars

• synthesis of fossil fuels: dead organisms compressed and transformed into coal, oil, and natural gas using heat and pressure

biotechnology

use of biological systems, living organisms, or their byproducts in the production of commercial goods

• humans used this well before it had a name

• fermented/cultured foods existed for 7000 years (ex: cheese, yogurt)

• ex: bacteria and yeast break down sugars

human microbiome

microorganisms (bacteria, archaea, viruses, fungi) living on and inside the human body

• are essential to the functioning of many of our body systems, believed to be a 1:1 ratio of your cells

• ex: digestive system, immune system, etc.

microbial bioremediation

the use of prokaryotes in pollution cleanup by breaking down/transforming toxic substances

• agricultural pollution: degrade excess fertilizers/pesticides

• toxic metals: certain prokaryotes can absorb up

• oil spills: petroleum consuming bacteria existing pre-spills, break down hydrocarbons