Lecture 16

Question 1

archaeal history

Answer 1

• activity of methanogens was first recognized by allesandro volta (1770) and first isolate in 1933
• recognized as a unique domain of life in late 1970s by woese
• they are as or more distantly related from bacteria as eukarya
• methanogens and extremophiles characterized the domain for many years

Question 2

what can archaea be classified as

Answer 2

• aerobic, facultatively anaerobic, or strictly anaerobic
• psychrophiles, mesophiles, thermophiles, and hyperthermophiles
• chemolithoautotrophs to chemoorganoheterotrophs -> no photosynthetic members
• inhabit marine, freshwater, sediments, and soil environments
• some are obligate symbionts but no known pathogens

Question 3

different major groups of archaea

Answer 3

3 superphyla
- asgardarchaeota
- DPANN
- TACK
1 large independent phylum
- euryarchaeota

• 6 of 27 phyla have cultivated members
• many not discovered via 16S rRNA -> shotgun metagenomic sequencing was used

Question 4

asgardarchaeota (lokiarchaeota)

Answer 4

• ancestors of eukaryotes
• loki’s castle deep sea hydrothermal vent field in the N atlantic was the source of lokiarchaeota
• monophyletic with the eukarya
• contains numerous eukaryotic signature proteins (actin/tubulin)
• likely to be the descendant of the archaeon that became the first eukaryote
• other phyla detected in estuary, groundwater and hot spring sediments

Question 5

Nanoarchaeota (DPANN)

Answer 5

• nanoarchaeota live in geothermal systems as obligate symbionts
• tiny cells with tiny genomes
• limited genetic and metabolic capabilities
• believed to have fermentative metabolism because no electron transport chains in genomes
• rely on other organisms (usually archeae) for essential biomolecules

Question 6

phylum nitrosphaeria -AOA (TACK phylum)

Answer 6

• aerobic ammonia oxidizing archaea = chemolithoheterotrophs and chemolithoautotrophs
• abundant in marine environments and terrestrial environments with low ammonium concentration
• thaumarchaeol lipids = tetraether lipid with cyclopentane rings forms lipid monolayer, especially present in thermophilic members

Question 7

euryarchaeota superphylum

Answer 7

• greatest number and diversity of cultivated and uncultivated lineages
• several phylum contain methanogens
• halophiles
• acidophiles
• thermophiles
• anaerobic methane and short chain hydrocarbon oxidation
• nitrite, sulfur, and iron reducing organisms

Question 8

phototrophs

Answer 8

• distributed across 7 phyla
• mainly anoxygenic (except cyanobacteria)
• diverse metabolisms and high degree of metabolic flexibility
• motility enables microbes in liquid environments to optimize position relative to light
  -> phototaxis

Question 9

different types of phototrophic microbes

Answer 9

• green sulfur
• green nonsulfur
• purple sulfur
• aerobic anoxygenic phototrophs
• cyanobacteria

Question 10

green sulfur bacteria

Answer 10

• phylum bacteroidota
• obligate anaerobes -> live in anoxic, sulfide rich zones in lakes
• fix CO2 via reductive TCA cycle (photolithoautotrophs) - sulfur is e- donor
• motility = non motile, or gliding, gas vesicles
• use chromosomes for photosynthesis

Question 11

chlorosomes

Answer 11

• found in green sulfur bacteria and green non sulfur bacteria
• contains bacteriochlorophyll and carotenoid pigments that harvest light
• surrounded by lipid monolayer
• linked to the reaction centers in the plasma membrane by FMO proteins
• light energy is transferred to the reaction centers in the membrane where the ETC and ATP synthase are located

Question 12

green non sulfur bacteria

Answer 12

• members of the phylum chloroflexi
• filamentous, gliding motility
• use chlorosomes
• not all green, not all non sulfur
• anaerobic or facultative
• autotrophs fix CO2 via 3-hydroxypropionate bi-cycle
  -> often photoheterotrophic
  -common in neutral to alkaline hot springs
• green to orange red mats

Question 13

purple non sulfur bacteria

Answer 13

• phylum proteobacteria, rhodobacterales orders
• found in lakes or ponds with organic matter and low sulfide
• photosynthetic apparatus in intracytoplasmic membranes (chromatophores)
• motile by flagella

Question 14

cyanobacteria

Answer 14

• only microbial phylum capable of oxygenic phototrophy
• diverse morphology, 1-10um unicellular or filamentous
  -> trichomes have individual plasma membrane and peptidoglycan but share periplasmic space and outer membrane
• cell division occurs in many ways
• differentiation - akinetes, heterocysts, hormogonia
• many are obligate photolithoautotrophs some can grow slowly in the dark as chemoheterotrophs
• CO2 fixation using the calvin cycle

Question 15

phycobilisomes

Answer 15

• located in thylakoid membrane associated with reaction centers
• stacks of phycocyanin and phycoerythrin pigments absorb light at different wavelengths and transfer them to reaction center via allophycocyanin
• chromatic acclimation = quantity of each pigment is modified depending on light wavelength availability
• radial protein complexes with 6 stacks

Question 16

budding, multiple fission

Answer 16

baeocyte -> division of cytoplasm to form basal cell and larger apical cell-> apical cell undergoes multiple rounds of division

• produces small cells that disperse easily

Question 17

gliding motility

Answer 17

• usually occurs in microbial mats by filamentous species
• mechanism not well understood, does not involve flagella
  -> rotating proteins in periplasmic space create moving ridges in cell wall
  -> share periplasmic space and outer membrane (individual cells with own inner membrane)

Question 18

cell differentiation

Answer 18

subgroup lV and V
- heterocysts = nitrogen fixation
-> thickening of cell wall, loss of phycobiliproteins and PSl, synthesis of nitrogenase

• akinetes
  -> thick walls, dormant
  -> dessication resistant

-hormogonia
-> small filaments
-> disperse easily
-> fragmentation

Question 19

prochlorophytes

Answer 19

• possess chlorophyll a,b, but no phycobilins
  -> only bacteria with chlorophyll b - ancestors of chloroplast
• prochloron = symbionts of sea squirts
• prochlothrix = free living, form filaments
• prochlorococcus = 1um cells with chlorophyll a and b
  -> most abundant photosynthetic organism on earth
  -> responsible for an enormous amount of CO2 fixation (1/3)
  -> high light and low light depth in ocean
  -> ratio of chlb:a = high in LL: high in HL

Question 20

chromatic adaptation

Answer 20

• relative amount of light harvesting pigments can be tuned to optimize photosynthesis in the environment
• sensory rhodopsins, phytochromes and other receptors sense the intensity and color of light
• gas vacuoles, gliding motility are used to position themselves optimally -> phototaxis