MBIO 1010 Study Guide - Final Guide: Epsilonproteobacteria, Primary Nutritional Groups, Lysis
31 May 2018
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MBIO 1010 - Summer 2018
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UNIT 4 – MICROBIAL DIVERSITY
Microbial Diversity
- Most prokaryotes cannot be cultured in the lab (yet)
- Some phyla are well studied in the lab (E. coli)
- Some are known only from 16S sequences or metagenomic studies
- Two ways to describe microbial diversity
1. Phylogenetic Diversity
o Microbes are grouped into phyla based on evolutionary relationships
o Most often based on 16S rRNA gene sequence (page 5-6)
2. Functional Diversity
o Groups microbes based on the activities they carry out
o Similar behaviours
Diversity of Bacteria
- Details to follow
1. Cyanobacteria
2. Proteobacteria
3. Firmicutes, Tenericutes
and Actinobacteria
4. Bacteroidetes
5. Chlamydiae and
Planctomycetes
6. Hyperthermophiles
7. Deinococcus-Thermus
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1. Cyanobacteria
o Impressive morphological diversity, generally larger than other bacteria
§ Unicellular, filamentous, or branching filaments
o Some form heterocysts
§ Specialized nitrogen-fixing cells
§ Example of limited differentiation in bacteria
• Bacteria usually do not have special cell types (binary fission)
o Only truly oxygenic photosynthetic microorganisms (see page 32)
§ Harvest energy from light and produce oxygen
o All are autotrophs
§ Fix CO2 to build cell material (Calvin cycle)
§ Doesn’t need existing carbon
§ Can fix carbon from CO2 and can also fix N2
o Like chloroplasts they carry out photosynthesis in specialized membranes called
thylakoids
o Unlike chloroplasts they have cell walls
§ Contain peptidoglycan
§ Gram negative cell wall type
o Widely distributed in terrestrial, freshwater, and marine habitats
o Lowest nutritional requirements of any organisms
§ Primary producers
o Ex. Prochlorococcus
§ One of the most abundant organisms on earth
§ Accounts for ~half of photosynthesis in the World’s oceans
2. Proteobacteria
o Includes many of the most commonly encountered
bacteria
§ Includes easily cultured bacteria (E. coli)
§ Best studied with most representatives
§ Your typical Gram-negative bacteria
o Most metabolically diverse phylum:
§ Chemolithotrophs (inorganic)
§ Chemoorganotrophs (organic)
§ Phototrophs (anoxygenic)
§ Facultative organisms that can switch from
one metabolic lifestyle to another
o Few unifying characteristics
o Many are pathogens of humans
o Divided into six classes
§ First three classes are well studied
§ Next two are smaller classes with broader
range of phenotypes
§ Last class is barely studied (difficult)
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i. Alphaproteobacteria
o Non-pathogenic
§ Ex. Rhizobium leguminosarum
• Forms root nodules on legume plants
• Has a symbiotic relationship with the plants
Ø Plants would not survive without it
• Bacterium fixes nitrogen into a bioavailable form
• Plant provides nutrients and a home for the bacteria
o Pathogenic
§ Ex. Rickettsia rickettsii
• Obligate intracellular pathogen
• Carried by insects and transmitted by insect bites
• Causes “Rocky Mountain spotted fever”
• Phylogenetically, Rickettsia is the closest relative to the eukaryotic
mitochondrion (see page 31)
ii. Betaproteobacteria
o Metabolically diverse, some are pathogens, some are non-pathogens
§ Ex. Neisseria mucosa
• Non-pathogenic commensal (surfaces) of the human body
§ Ex. Neisseria gonorrhoeae
• Pathogenic, causes the STI gonorrhea
• Functionally different compared to N. mucosa
iii. Gammaproteobacteria
o Metabolically and ecologically diverse
o Many grow well in the lab and become important research models
§ Ex. Escherichia coli (E. coli)
• Gram negative, rod shaped, facultative aerobe, motile by means of
peritrichous flagella
• Ferments lactose to a mixture of acids and alcohols (and soil)
• Resident of the large intestine od warm-blooded animals
• Serves as an important indicator of fecal contamination
Ø Indicator of poop, and precursor for any other bacteria that
could be present in given samples
§ Ex. Pseudomonas aeruginosa
• Gram negative, rod shaped, motile by means of polar flagella, but does
not ferment sugars
• Naturally resistant to many antibiotics and disinfectants
Ø Does not acquire resistance, but just always had it
• Opportunistic pathogen
Ø Causes infections in immunocompromised (poor immune
system) patients
Ø Not a big risk to anyone except the poor immune systems
• Very tough to kill
Ø Antibacterial agents are just food to P. ae
• Ex. Respiratory tract infections in cystic fibrosis patients
Ø Too much mucous, number one cause of death for CF
Document Summary
Most prokaryotes cannot be cultured in the lab (yet) Some phyla are well studied in the lab (e. coli) Some are known only from 16s sequences or metagenomic studies. Details to follow: cyanobacteria, proteobacteria, firmicutes, tenericutes and actinobacteria, bacteroidetes, chlamydiae and. Impressive morphological diversity, generally larger than other bacteria. Unicellular, filamentous, or branching filaments: some form heterocysts. Example of limited differentiation in bacteria: bacteria usually do not have special cell types (binary fission, only truly oxygenic photosynthetic microorganisms (see page 32) Harvest energy from light and produce oxygen: all are autotrophs. Fix co2 to build cell material (calvin cycle) Can fix carbon from co2 and can also fix n2: like chloroplasts they carry out photosynthesis in specialized membranes called thylakoids, unlike chloroplasts they have cell walls. Gram negative cell wall type: widely distributed in terrestrial, freshwater, and marine habitats, lowest nutritional requirements of any organisms. One of the most abundant organisms on earth.
