Eubacteria and archaea
In a single spoonful of garden soil live more bacteria than there are people on the whole planet. They are the oldest, most numerous and most metabolically versatile organisms on Earth: there are bacteria that breathe sulfur, that make oxygen, that live at 110 °C or that survive in saturated brines. To understand microbial life, we have to start with its cell.
The prokaryotic cell
Under the microscope, a stained cheek cell shows a dark, well-defined nucleus, whereas the bacteria in yoghurt look uniform, with no visible internal compartments: where do they keep their genetic material if they have no nucleus?
State three structural differences between a bacterial prokaryotic cell and a eukaryotic cell, and explain the functional consequence of each one.
State three structural differences between a bacterial prokaryotic cell and a eukaryotic cell, and explain the functional consequence of each one.
Bacterial shapes and groupings
Look at the bacteria in the diagram (A to F). Classify them according to their shape (coccus, bacillus, spirillum, or vibrio) and, where applicable, according to their…
Look at the bacteria in the diagram (A to F). Classify them according to their shape (coccus, bacillus, spirillum, or vibrio) and, where applicable, according to their arrangement (diplococci, streptococci, staphylococci), giving a well-known example where possible.
Cell wall, capsule, flagella, pili and endospores
If you immerse a red blood cell in distilled water, it swells rapidly until it bursts by osmosis, but a freshwater bacterium never bursts: what mechanical structure withstands that enormous internal osmotic pressure?
Explain what the bacterial cell wall is (peptidoglycan) and what the Gram stain consists of: which two major groups it distinguishes (Gram-positive and Gram-negative)…
Explain what the bacterial cell wall is (peptidoglycan) and what the Gram stain consists of: which two major groups it distinguishes (Gram-positive and Gram-negative) and why it is so useful for choosing a treatment.
a) Name three external structures that a bacterium can have. b) Explain the main function of each of them.
- a) Name three external structures that a bacterium can have.
- b) Explain the main function of each of them.
What is an endospore? Explain how it forms, what extraordinary resistance it has (heat, desiccation, disinfectants) and why it complicates sterilisation in medicine and…
What is an endospore? Explain how it forms, what extraordinary resistance it has (heat, desiccation, disinfectants) and why it complicates sterilisation in medicine and in canned food (examples: tetanus, botulism).
Bacterial metabolism and ecological role
Bacterial metabolism is very diverse. Describe photoautotrophic, chemoautotrophic, and heterotrophic types: where each obtains energy and carbon from, and give an…
Bacterial metabolism is very diverse. Describe photoautotrophic, chemoautotrophic, and heterotrophic types: where each obtains energy and carbon from, and give an example of a bacterium or environment for each type.
Distinguish between a strict aerobic bacterium, a strict anaerobic one and a facultative anaerobic one, and associate each type with an environment (the soil surface,…
Distinguish between a strict aerobic bacterium, a strict anaerobic one and a facultative anaerobic one, and associate each type with an environment (the soil surface, the bottom of a deep wound, the digestive tract).
Explain the essential role of bacteria in the nitrogen and carbon cycles (fixation, nitrification, denitrification, and decomposition) and reason what would happen to…
Explain the essential role of bacteria in the nitrogen and carbon cycles (fixation, nitrification, denitrification, and decomposition) and reason what would happen to ecosystems if they disappeared.
Two domains: eubacteria and archaea
In the late 1970s, Carl Woese compared ribosomal RNA sequences and discovered that microbes from volcanic hydrothermal vents differed more from Escherichia coli than the latter does from a plant: how can two organisms with identical appearance under the microscope belong to such different lineages?
Many archaebacteria are extremophiles (thermophiles, halophiles, acidophiles). Describe which environments they colonise, what biochemical adaptations allow them to live…
Many archaebacteria are extremophiles (thermophiles, halophiles, acidophiles). Describe which environments they colonise, what biochemical adaptations allow them to live there, and why studying them is relevant to hypotheses about the origin of life.
State two molecular differences between eubacteria and archaebacteria (for example in the cell wall or membrane lipids) and explain why they are classified into…
State two molecular differences between eubacteria and archaebacteria (for example in the cell wall or membrane lipids) and explain why they are classified into different domains.
Cyanobacteria were called "blue algae" for centuries. Explain why that name was incorrect (prokaryotic organisation), which photosynthesis they perform (oxygenic) and…
Cyanobacteria were called "blue algae" for centuries. Explain why that name was incorrect (prokaryotic organisation), which photosynthesis they perform (oxygenic) and what historical role they played in the Earth's atmosphere.
Horizontal gene transfer
Bacteria usually reproduce by binary fission, but they can acquire DNA without reproducing. Transformation takes up free DNA; transduction carries it by means of bacteriophages; conjugation involves transfer by contact between cells, often of plasmids.