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Microbial Physiology and Growth > Week 5 - Photolithotrophy and Photoorganotrophy > Flashcards

Week 5 - Photolithotrophy and Photoorganotrophy Flashcards

1
Q

Photolithotrophy and photoorganotrophy are

A

modes of bacterial metabolism

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2
Q

All living things need

A
  • a source of raw materials
  • a source of energy
  • a source of reducing power (electrons)
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3
Q

Living things can be classified

A

according to their metabolism, on the basis of where they get these things from
• in the case of “raw materials” classification is usually on the basis of carbon source

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4
Q

Examples of bacterial metabolism

A
  • chemoorganotrophs
  • photoautotrophs
  • photolithotrophs
  • chemolithotrophs
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5
Q

Phototrophs

A

“light eaters”
• obtain energy from sunlight
• photoorganotrophs and photolithotrophs

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6
Q

Photoorganotrophs

A

obtain energy from sunlight

• electrons and carbon from organic sources

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7
Q

Photolithotrophs

aka photoautotrophs, photolithoautotrophs

A

obtain energy from sunlight
• electrons from inorganic sources
• carbon from CO2

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8
Q

Cyanobacteria (and plants) are one sort of

A

photolithotroph

• their inorganic source of electrons is water

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9
Q

Many bacteria can

A

switch between modes of growth

photolithotrophs and photoorganotrophs?

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10
Q

Phototrophy

A
  • photosynthesis
  • chlorophylls and bacteriochlorophylls
  • carotenoids and phycobilins
  • anoxygenic photosynthesis
  • oxygenic photosynthesis
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11
Q

Photosynthesis

A

the conversion of light energy to chemical energy
• phototrophs carry out photosynthesis
• most phototrophs are also autotrophs
• photosynthesis requires light-sensitive pigments called chlorophylls
• photoautotrophy requires ATP production and CO2 reduction

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12
Q

… carry out photosynthesis

A

phototrophs

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13
Q

Most phototrophs are also

A

autotrophs

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14
Q

Phototrophs

A

all use light as energy source

use CO2 = photoautotrphs

use organic carbon = photoheterotrophs

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15
Q

Chlorophylls and bacteriochlorophylls

A

• organisms must produce some form of chlorophyll (or bacteriochlorophyll) to be photosynthetic
• chlorophyll is related to porphyrins
• number of different types of chlorophyll exist
- different chlorophylls have different absorption spectra

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16
Q

Chlorophyll is related to

A

porphyrins

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17
Q

Different chlorophylls have different

A

absorption spectra

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18
Q

Photoautotrophy

A
  • oxidation of H2O produces O2 = oxygenic photosynthesis

* oxygen not produced = anoxygenic photosynthesis

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19
Q

Oxygenic photosynthesis

A

oxidation of H2O produces O2

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20
Q

Anoxygenic photosynthesis

A

oxygen not produced

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21
Q

Cyanobacteria produce

A

chlorophyll a

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22
Q

Prochlorophytes produce

A

chlorophyll a and b

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23
Q

Anoxygenic phototrophs produce

A

bacteriochlorophylls

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24
Q

Chlorophylls arelocated within special membranes

A
  • in eukaryotes called thylakoids

* in prokaryotes, pigments are integrated into cytoplasmic membrane

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25
Q

Pigment of purple bacteria

A

Bchl a and b

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26
Q

Pigment of green sulfur bacteria

A

Bchl c, d, e

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27
Q

Pigment of green nonsulfur bacteria

A

Bchl cs

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28
Q

Pigment of heliobateria

A

Bchl g

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29
Q

Reaction centers

A

participate directly in the conversion of light energy to ATP

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30
Q

Antenna pigments

A

funnel light energy to reaction centers

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31
Q

Chlorosomes

A 
function as massive antenna complexes
• found in green sulfur bacteria and green nonsulfur bacteria
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32
Q

Phototrophic organisms have accessory pigments in addition to chlorophyll, including

A

carotenoids and phycobiliproteins

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33
Q

Carotenoids

A
  • always found in phototrophic organisms
  • typically yellow, red, brown, or green
  • energy absorbed by carotenoids can be transferred to a reaction center
  • prevent photooxidative damage to cells
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34
Q

Energy absorbed by carotenoids can be transferred to

A

a reaction center

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35
Q

Carotenoids prevent

A

photooxidative damage to cells

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36
Q

Phototrophs:

purple and green bacteria

A

anoxygenic
• reducing power from H2S (e-) –> S0 (e-) –> SO4 2-
• energy from ADP + light = ATP (to carbon source)
• carbon from CO2 + electrons from H2S + energy from ATP == (CH2O)n
(n subscript)

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37
Q

Phototrophs:

cyanobacteria, algae, green plants

A

oxygenic
• reducing power from H2O (e-) –> 1/2 O2
• energy from ADP + light = ATP (to carbon source)
• carbon from CO2 + electrons from H2O + energy from ATP == (CH2O)n
(n subscript)

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38
Q

Phycobiliproteins

A

main antenna pigments of cyanobacteria and red algae
• form into aggregates within the cell called phycobilisomes
• allow cells to capture more light energy than chlorophyll alone

39
Q

Anoxygenic photosynthesis specific

A
  • found in 4 phyla of bacteria
  • photosynthesis apparatus embedded in membranes
  • electron transport reactions occur in the reaction center of anoxygenic phototrophs
40
Q

Anoxygenic photosynthesis

reducing power

A

reducing power for CO2 fixation comes from reductants present in the environment
(H2S, Fe2+, or NO^2-)
• requires reverse electron transport for NADH production in purple phototrophs
• electrons are transported in the membrane through a series of proteins and cytochromes

41
Q

Anoxygenic photosynthesis

• for a purple bacterium to grow autotrophically, the formation of ATP is not enough

A
  • reducing power (NADH) is also necessary
  • reduced substances such as H2S are oxidized and the electrons eventually end up in the quinone pool of the photosynthetic membrane
42
Q

How photosynthesis works

A
  • photons are absorbed by pigments (chromophores)
  • the energy from the photons is used to pump protons (H+) across a membrane (also used to drive redox reactions)
  • energy stores in proton gradients is used to drive ATP synthesis
43
Q

Nature has invented photosynthesis twice

A

a) photosynthesis based on chlorophyll (in eubacteria)

b) photosynthesis based on bacteriorhodopsin (best characterized in archaea, but now known in some eubacteria)

44
Q

Oxygenic photosynthesis specifics

A
  • oxygenic phototrophs use light to generate ATP and NADPH
  • the 2 light reactions are called photosystem I and photosystem II
  • Z scheme of photosynthesis (photosystem II transfers energy to photosystem I)
  • ATP can also be produced in CYCLIC PHOTOPHOSPHORYLATION
45
Q

Oxygenic phototrophs use light to generate

A

ATP and NADPH

46
Q

Z scheme of photosynthesis

A

photosystem II transfers energy to photosystem I

in oxygenic photosynthesis

47
Q

Chlorophyll photosynthesis

A 
in bacteria
• proteobacteria
• gram positive bacteria
• cyanobacteria
• chloroplast
48
Q

Bacteriorhodopsin photosynthesis

A

in archaea

• extreme halophiles

49
Q

Photosynthetic bacteria and where they get their electrons from:
photolithotrophs

A
  • cyanobacteria: electrons from water, H2O
  • purple sulfur bacteria: electrons from sulfides eg H2S
  • green sulfur bacteria: electrons from sulfides
50
Q

Photosynthetic bacteria and where they get their electrons from:
photoorganotrophs

A 
all get electrons from organic molecules
• purple non-sulfur bacteria
• green non-sulfur bacteria
• heliobacteria
• Halobacterium (archaebacterium, bacteriorhodopsin)
51
Q

Winogradsky column - redox gradient

A

aerobic
microaerophilic (water-soil junction)
anaerobic
H2S

52
Q

Winogradsky column - microbial zones

A
  • water (aerobic) = algae, cyanobacterium, aerobic heterotrophs
  • junction (microaerophilic) = H2S oxidizers, facultative anaerobes
  • red-brown (anaerobic-ish) = purple non-sulfur photoheterotrophs
  • red-violet (anaerobic) = purple sulfur bacteria
  • green-gray (anaerobic) = green sulfur bacteria
  • bottom sediment (H2S) sulfate reducters, fermentnative heterotrophs
53
Q

Photoorganotrophs obtain their electrons and some energy

A

by oxidizing organic compounds
• if you have access to organic compounds as a foodstuff, why bother with photosynthesis?
- depends of availability of oxygenic

photoorganotrophs are either

a) obligate anaerboes (eg Heliobacteria)
b) chemoorganotrophs when oxygen is present - they switch to photosynthesis under anaerobic conditions (eg Halobacteria, purple-nonsulfur bacteria, green non-sulfur bacteria)

54
Q

Photoorganotrophs are either

A

a) obligate anaerboes (eg Heliobacteria)
b) chemoorganotrophs when oxygen is present - they switch to photosynthesis under anaerobic conditions (eg Halobacteria, purple-nonsulfur bacteria, green non-sulfur bacteria)

55
Q

Photoorganotrophs

in he absence of oxygen

A

only very limited energy can be obtained by breaking down organic molecules (see chemoorganotrophy and fermenation)
• therefore under anaerobic conditions a huge advantage to be able to obtain extra energy from light

56
Q

Halobacterium salinarum

A
  • photoorganotroph that is chemoorganotroph when oxygen is present, switch to photosynthesis under anaerobic conditions
  • make water red
57
Q

When oxygen is present, Halobacterium grow as

A

a chemoorganotroph

58
Q

Under anaerobic conditions, Halobacterium

A

synthesizes large quantities of bacteriorhodopsin, a plasma membrane protein with a retinal chromophore
• when it absorbs a photon, the retinal changes conformation - this drives changes in protein structure, leading to pumping of protons across the membrane

59
Q

Purple non-sulfur bacteria

A

gram-negative eubacteria
• eg Rhodospirillium rubrum
• lives in muddy sediments in lakes and ponds
• adjusts its metabolism according to the availability of light, oxygen, organic compounds and sulfide
• it can be a photoorganotroph, an aerobic chemoorganotroph, or an anaerobic chemoorganotroph, or a lithotroph that uses the Calvin cycle to fix CO2

60
Q

Under aerobic conditions, Rhodospirillum is

A

colorless and grows as a chemoorganotroph
• under anaerobic conditions, cells become purple (mainly due to carotenoids). at the same time, it synthesizes chromatophore membranes containing photosynthetic proteins which bind bacteriochlorophyll

61
Q

Bacteriochlorophylls absorb light energy strongly in the near

A

infra-red
• the key protein complex is a reaction center which uses light-energy to drive movement of electrons
• electron flow is coupled to proton translocation across the chromatophore membrane
• see reaction center cytochrome bc complex
electron flow is cyclic - normally no net generation of oxidant or reductant

62
Q

The reactin center of purple non-sulfur bacteria is a

A

Type 2 reaction center

• it shows some resemblance to Photosystem II of cyanobacteria and plants

63
Q

Green non-sulfur bacteria

A
  • Chloroflexus and relatives
  • Chloroflexus forms thick mats, often in warm springs
  • a motile, filamentous, gliding bacterium
  • grows as a chemoorganotroph in the dark, switches to photoorganotrophy under anaerobic conditions in the light
  • like Rhodospirillum, Chloroflexus has a Type 2 reaction center but it doesn’t make chromatophores
  • the reaction center is in the plasma membrane, and is associated with chlorosomes
64
Q

Forms thick mats, often in warm springs

A

Chloroflexus

green non-sulfur bacteria

65
Q

Like Rhodospirillum, Chloroflexus has a

A

Type 2 reaction center
BUT
doesn’t make chromatophores
• reaction center is in the plasma membrane and is associated with chlorosomes

66
Q

Heliobacteria

A

obligate anaerobes found in sediments in paddy fields
• gram-positive cell structure - not closely related to any phototrophs
• photosynthesis based on a Type 1 reaction center
(shows resemblance to Photosystem I of cyanoabcteria and plants)

67
Q

Photolithotrophs

A
  • purple sulfur bacteria (electrons from sulfides, eg H2S)
  • green sulfur bacteria (electrons from sulfides)
  • cyanobacteria (electrons from water, H2O)
68
Q

Purple sulfur bacteria get electrons from

A

sulfides

eg H2S

69
Q

Green Sulfur bacteria get electrons from

A

sulfides

70
Q

Cyanobacteria get electrons from

A

water H2O

71
Q

Purple sulfur bacteria

A

eg Chromatium vinosum
• strict anaerobes
• found in sulfur springs, in anaerobic lake sediments
• photosynthetic apparatus very similar to purple non-sulfur bacteria
but pathways of electron flow are different
• instead of cyclic electron flow, electrons are extracted to form sulfides (oxidized to sulfur, and then to sulphate)
and are used to reduce NAD+ to NADH which is used to fix CO2 via the Calvin cycle
• often deposit sulfur granules inside the cell

72
Q

Green sulfur bacteria

A

eg Chlorobium
• filamentous, gliding bacteria
• strict anaerobes
• found in anaerboic zones of lakes, plus sulfur springs
• photosynthesis based on a Type 1 reaction center but have chlorosomes (like Chloroflexus)
• electrons extracted from sulfides, used to reduce NAD+ to NADH
• carbon obtained from CO2 (but not fixed via the Calvin cycle)

73
Q

Cyanobacteria (blue-green algae)

A
  • electrons from water
  • used eventually to reduce NADP to NADPH
  • ATP and NADPH used (eg) in the Calvin cycle, which fixes CO2
  • extracting electrons from water, and passing them to NADP requires some difficult chemistry, and a very high energy input
  • cyanobacteria do this by using 2 kinds of reaction centers acting in series (Z scheme)
74
Q

Photosystem II

A

a Type 2 reaction center

• resemblance to the reaction centers of purple bacteria and Chloroflexus - but with an extra unit that oxidizes water

75
Q

Photosystem I

A

a Type 1 reaction center

• resemblance to the reaction centers of green sulfur bacteria and heliobacteria

76
Q

Synechocystis 6803

A

thylakoid membranes

phycobilisomes

77
Q

Cyanobacteria are related to chloroplasts of

A

green plants and algae

• green plants retain Photosystem II and Photosystem I but have lost phycobilisomes

78
Q

Cyanobacteria probably evolved 3-3.5 billion years ago and

A

were responsible for generating the oxygen-rich atmosphere

79
Q

How did cyanobacteria evolve in the first place?

A

purple and green bacteria have a simpler photosynthetic apparatus, and are assumed to have evolved first
• but cyanobacteria combine a Type II reaction center and a Type I reaction center

80
Q

Cyanobacteria are very

A

widespread - lakes, rivers, oceans

wide range of different lifestyles and morphologies
• some form mats, some float

range from small single cells to complex filaments

81
Q

Prochlorococcus marinus and

Anabaena cylindrica are both

A

cyanobacteria
• Prochlorococcus (1.67 MB, 1696 genes) has small, simple cells
• Anabaena (6.37 MB, 6132 genes) filamentous, multiple cell types

82
Q

Metabolic versatility in cyanobacteria

A

eg Oscillatoria limnetica
• a filamentous cyanobacterium found in a warm, sulfide-rich spring in New Zealand
• during the night: sulfide builds up in the spring
• in the morning: Oscillatoria grows like a green sulfur bacterium, using sulfide as a source of electrons, and only Photosystem I
• later in the day: all the sulfide gets used up, and Oscillatoria grows like a normal cyanobacterium, using Photosystem II to extract electrons from water

83
Q

Strucutral complexity in cyanobacteria

A

eg Anabaena variabilis
• heterocyst
• vegetative cells

84
Q

Heterosystes are one solution to the problem of

A

fixing nitrogen while doing oxygenic photosynthesis
• nitrogen is fixed by nitrogenase
electrons + ATP + H+ + N2 –> NH3 + H2
• the problem is NITROGENASE IS INACTIVATED BY OXYGEN

85
Q

So nitrogen fixation and oxygen evolution must

A

be separated, either in time or space

86
Q

Heterocysts

A

fix nitrogen
• they keep the environment inside the cell anaerobic by having no photosystem II, by having a high content of respiratory oxidases, and by having a thick, oxygen-impermeable cell wall

87
Q

Heterocysts and vegetative cells

A

depend on each other
• vegetative cells make sugars
• heterocysts make nitrogen compounds (amino aids)
• the different chemicals are exchanged between the cells
• so Anabaena is a true multicellular organism

88
Q

Vegetative cells make

A

sugars

89
Q

Heterocysts make

A

nitrogen compounds (amino acids)

90
Q

Filamentous cyanobacteria are

A

multicellular organisms
• morphological development
Anabaena in nitrogen-rich environment = no heterocyst
Anabaena in nitrogen-poor environment = heterocyst forms

91
Q

cyanobacteria

A

electrons from water, H2O

92
Q

purple sulfur bacteria

A

electrons from sulfides eg H2S

93
Q

green sulfur bacteria

A

electrons from sulfides

Microbial Physiology and Growth (5 decks)

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