Key Terms
Prokaryotes
Unicellular organisms with no nucleus and no membrane-bound organelles. Two domains: Bacteria and Archaea.
Human body
Bacteria were once estimated to outnumber human cells 10:1; revised estimates suggest closer to 1:1. Found in: mouth, na
Carbon fixation
Conversion of CO2 into organic carbon products; animals and plants rely on prokaryotes for this. Nitrogen fixation: conv
Mutualism
Bacteroides thetaiotaomicron digests complex polysaccharides humans cannot; converts them to absorbable monosaccharides.
Amensalism
Staphylococcus epidermidis and Propionibacterium acnes produce bacteriocins and bacteriocin-like compounds that kill oth
Commensalism
S. epidermidis feeds on dead skin cells; humans are unaffected.
Neutralism
Metabolically active Bacillus anthracis bacteria coexisting with ungerminated B. anthracis endospores; neither affects t
Parasitism
Pathogenic bacteria that invade the human body and produce toxins. Tetanus, diphtheria, pertussis, tuberculosis, and lep
Microbiome
All prokaryotic and eukaryotic microorganisms and their genetic material associated with a given organism or environment
Microbiota
The microorganisms living in a specific region of the body (e.g., oral microbiota, gut microbiota). Resident microbiota:
Inner cheek
Least diverse (high oxygen exposure); dominated by Streptococcus. Tongue crypts and spaces between teeth: more diverse;
Before birth
Rapid increase in vaginal Lactobacillus spp.; this is the first colonization source during natural birth. After birth: a
Bacteroides
~30% of gut microbiome; one gram of feces contains up to 100 billion Bacteroides cells; prevent pathogens from colonizin
Gram-positive
Thick peptidoglycan wall retains crystal violet (primary stain); appear purple after staining. Gram-negative: thin pepti
Bdellovibrio
Parasites of other gram-negative bacteria; invade host; position in periplasm (between plasma membrane and cell wall); f