Mic 105 Midterm 2

Front 1

What type of organisms have chlorophyll-based phototrophy besides plants?

Back 1

Only in bacteria (and chloroplasts)

Front 2

What are the two types of chlorophyll-based phototrophy?

Back 2

oxygenic
anoxygenic

Front 3

Oxygenic chlorophyll-based phototrophy

Back 3

only in cyanobacteria (and chlorophyll/plants)

O2 is produced as byproduct
primarily photoautotrophs

Front 4

Anoxygenic chlorophyll-based phototrophy

Back 4

currently known in 4 bacterial lineages
O2 not produced or required
most do it anaerobically

photoautotrophs and photoheterotrophs

Front 5

What are the common features of photosynthetic apparatus?

Back 5

1. Photosynthetic pigments- absorb different wavelengths of light. Give bacteria their characteristic color.

2. Photosystem(s): I or II (cyanobacteria have both)

3. Reaction center (RC) - has a special form of Chlorophyll bound to specific photosynthesis proteins in the photosynthetic membrane, connected to ETC.

4. Accessory pigments

5. Produces reduced NAD(P)H for biosynthesis and CO2 fixation (mechanisms differ)

Front 6

What do accessory pigments do?

Back 6

increase efficiency of proton absoption

Front 7

Chlorophylls

Back 7

tetrapyrrole ring with bound Mg2+

in cyanobacteria and plants

Front 8

Bacteriochlorophylls:

Back 8

differ in side groups and wavelengths absorbed

-in purple and green phototrophs

Front 9

Phycobiliproteins

Back 9

only in cyanobacteria, chloroplasts, and some algae

red or blue pigments (open chain tetrapyrroles) attached to proteins

Embedded in the membrane
Allow growth at low light intensities

Front 10

Carotenoids

Back 10

long chain hydrocarbons with extensive conjugated double bonds

Embedded in the membrane. transfer light energy to the photosynthetic reaction center

protective effect - intercept toxic forms of oxygen that are formed in various photochemical and biochemical reactions

Front 11

Cyanobacteria habitat

Back 11

found in most environments: soil and water and anywhere there is light

Found in permanently frozen Antarctic lakes, hot springs up to about 70C, oceans, deserts, salt marshes, rocks, Predominate most microbial mats

Front 12

Cyanobacteria physiology

Back 12

oxygenic photoautotrophs (most obligate); some can grow slowly as organoheterotrophs in the dark

Many fix N2

Two separate light reactions are involved, photosystems I and II splits H2O to provide electrons for Co2 fixation

O2 is produced as a by-product

Some can carry out anoxygenic PS with H2S as electron donor (using only PSI)

Use Calvin cycle to fix CO2

Front 13

Cyanobacteria pigments

Back 13

Chlorophyll a, carotenoids, phycobilins

Phycobilins are complexed to phycobiliproteins in large aggregates called phycobilisomes that are attached to photosynthetic membranes (thylakoids)

Production controlled by light intensity- more made in low light

Front 14

Purple phototrophs are anoxygenic phototrophs that obtain carbon either...

Back 14

from CO2 + H2S/H2 (photoautotrophic - preferred growth strategy of purple sulfur bacteria)

or organic compounds (photoheterotrophic - preferred growth strategy of purple nonsulfur bacteria)

Photosystem II

Use the Calvin cycle to fix CO2

Most fix Nitrogen

Front 15

Cyclic photophosphorylation in anoxygenic phototrophs which results in ________________

Back 15

proton pumping and generates PMF

Front 16

NAD(P)H is generated by ________________ in cyclic photophosphorylation

Back 16

reverse electron transport which uses the same electron carriers as electron transport, but runs in reverse driven by the energy of PMF

Front 17

Purple sulfur bacteria habitat

Back 17

Gamma proteobacteria

anaerobic environments with H2S and light. marine environments, freshwater muds, sulfur springs

Front 18

Purple sulfur bacteria morphology

Back 18

large unicellular - up to 6 uM in diameter. many motile by polar flagella

Front 19

Purple non-sulfur bacteria morphology and habitat

Back 19

widespread in soils and water

alpha and beta proteobacteria

unicellular rods, oval, spirilla, cells smaller than PS, some divide by budding. some have a dimorphic lifestyle and have stalks, many are motile by polar flagella

Front 20

Purple sulfur bacteria physiology

Back 20

most are obligate photoautotrophs using H2S converting it to S0 and depositing it inside cells as granules. most also use S0 as e- source

some can grow as organoheterotrophs or chemolithotrophs under aerobic or microaerophilic conditions in the dark

Front 21

Purple nonsulfur bacteria physiology

Back 21

metabolically very versatile. preferred mode of growth; anaerobic heterotrophs. most also grow as photoautotrophs using H2 or H2S; sensitive to high H2S

When using H2S, they deposit sulfur granules outside or convert it to sulfate.

some ferment w/o O2 in the dark. most grow as aerobic organoheterotrophs

Front 22

Green sulfur bacteria physiology

Back 22

Chlorobi

anoxygenic photoautotrophs, use H2S or H2 as the electron donor

some grow as photoheterotrophs using simple organic carbon sources

strict anaerobes

Front 23

Green nonsulfur bacteria physiology

Back 23

Chloroflexi

Preferred physiology: photoheterotrophs using sugars, organic acids or amino acids as C-sources

photoautotrophs with H2 or H2S (sensitive to high H2S)

can grow as aerobic organoheterotrophs

Front 24

Green sulfur bacteria habitat

Back 24

Freshwater and marine sediments

grow at ~25% of the light required by PS, PNS, or GNA bacteria

high tolerance to H2S, low pH, can live deepest in sediments where sulfate reduction and fermentation occur and light is very low

Front 25

Green non sulfur bacteria habitat

Back 25

Alkaline hot springs; many thermophilic; freshwater and marine environments

Front 26

Green sulfur bacteria morphoology

Back 26

small nonmotile unicellular rods

Front 27

Green nonsulfur bacteria morphology

Back 27

typically multicellular filaments, motile by gliding

Front 28

Green sulfur bacteria metabolism

Back 28

Fix CO2 by reductive (reverse) TCA cycle

can reduce NAD(P)+ directly; do not need to use reverse electron transport

PSI only

Front 29

Green nonsulfur bacteria metabolism

Back 29

Use 3-hydroxyproprionate pathway to fix CO2

can reduce NADP directly do not need to use reverse electron transport

PSII

Front 30

Heliobacteria

Back 30

low GC gram positive endosporeformers, closely related to Clostridium

Front 31

Heliobacteria physiology

Back 31

Anoxygenic photoheterotrophs:

cannot fix CO2
heterotrophic growth in the dark by fermenting pyruvate and other organic acids
strict anaerobes

Front 32

Heliobacteria morphology

Back 32

rod shaped, endospores formed

Front 33

Heliobacteria habitat

Back 33

found in anaerobic alkaline soils, rice paddies, can fix nitrogen

Front 34

NADPH Generation in Green Bacteria and Heliobacteria

Back 34

Electrons from H2 or H2S reduce ferredoxins in the electron transport pathway, and these are sufficiently electronegative to reduce NADP/NAD directly without additional energy from the PMF. Therefore, reverse electron transport not required.

Front 35

Anoxygenic phototrophy: summary

Back 35

Phototrophic under anaerobic conditions; Do not produce O2 Have either PSI or PSII, not both Purple bacteria and green nonsulfur (chloroflexi) have PSII Green sulfur bacteria (chlorobi) and heliobacteria have PSI
e- from H2, H2S, Fe2+, NO2-, organic compounds (contrast: H2O for oxygenic phototrophy