Bacterial Nutrition - Lecture 3

Question 1

What key elements do bacteria need

Answer 1

96% - CHNOPS (Carbon, Phosphorus, Nitrogen)
4% - Na, K, Cl, Mg, Fe, and trace elements

Question 2

Acquisition of carbon in autotrophs

Answer 2

• Fixation of inorganic carbon (CO2)
• Cyanobacteria, green and purple sulphur bacteria

Question 3

Acquisition of carbon in heterotrophs

Answer 3

• Assimilation of organic carbon
• Simple sugars (most bacteria)
• Complex sugars (actinomycetes and gliding bacteria)

Question 4

Acquisition of nitrogen in assimilation

Answer 4

• NH4, NO3, Organic N (e.g. amino acids)
• Most bacteria

Question 5

Acquisition of nitrogen in nitrogen fixing

Answer 5

• N2
• Some cyanobacteria and actinomycetes

Question 6

Acquisition of phosphorus

Answer 6

Assimilation of PO4

Question 7

Other resources and conditions required for growth

Answer 7

H, O, S, Na, K, Cl, Mg, Fe
Trace elements Cu, Mn, Zn
Appropriate temp, pH, salinity
Electron donor
Energy source

Question 8

How are bacteria categorised by growth requirements?

Answer 8

Source of energy
- Phototroph (light)
- Chemotroph (Chemical reactions)

Source of electrons
Organotroph (Organic matter)
Lithotroph (Inorganic compounds)

Source of carbon
Autotroph (inorganic C)
Heterotroph (organic C

Question 9

What categories do photolithoautotrophs come under

Answer 9

Phototroph (source of light energy)
Lithotroph (inorganic compounds)
Autotroph (Inorganic C)

Question 10

What is a guild?

Answer 10

Group of species which exploit same class of environmental resources in similar way

Question 11

Bacterial guild A - Aerobic Decomposers

Answer 11

Chemoorganheterotrophs

3 DOC + O2 -> 2CO2 + H2O

Utilise DOC for energy, carbon and electrons

Largest group of aerobic bacteria

Core genus: Pseudomonas

Other examples: Legionella, Vibrio, Azomonas

Disease causing

Bacteria mostly associated with eukaryotes

Mineralisers: Organic to inorganic C

Question 12

Bacterial guild B - Gliding bacteria

Answer 12

Chemoorganoheterotrophs

3POC + O2 -> DOC and CO2 + CO2 + H2O

Utilise POC for energy, carbon, electrons

Decompose POC to DOC

Mineralisers - DOC - CO2

Cellulose, chitin, pectin, keratin. Some degrade agar

Core genus: Cytophaga

Other genera: Sporocytophaga, Flexibacter, Myxococcus

No flagella

Question 13

Bacterial guild E - Sulphate reducing bacteria

Answer 13

Chemoorganoheterotrophs

3DOC + SO42- -> CO2 + DOC + H2S

High DOC conc in anaerobic environments

SO4 is most abundant electron acceptor

Anaerobic respiration

Dissimilatory sulphate reduction

2nd largest bacterial guild

Desulfovibrio, Desulfuromonas, Desulfotomaculum

H2S end product

Question 14

Bacterial guild F - Green and Purple bacteria

Answer 14

Photolithoautotrophs

2CO2 + H2S + Light -> H2O + SO42- + DOC

Anoxygenic photosynthesis

Bacteriochlorophyll - Bchl a and b (purple), Bchl c, d, and e (green)

Sulphide is electron source

Infra-red used to fix CO2

Sulphur granules: in cell (purple), outside cell (green)

Purple: Chromatium, Thiospirillum

Green: Prosthecochloris, Pelodictyon

Up to 10 micrometers long

Question 15

Bacterial guild D - Colourless sulphur bacteria

Answer 15

Chemolithoautotrophs - aerobic

O2 + CO2 + 2H2S -> SO4+ + H2O

Electron donor abundant in anaerobic environment

Thiobacillus, Thiospira, Thiomicrospira

Acid tolerant - extreme environments

Oxidises iron, leach metals

Question 16

Outline sulphur cycle

Answer 16

SO4 -> (Guild E) -> H2S
H2S -> (Guild D, Guild F) -> SO4

Question 17

Guild C: Nitrifying bacteria

Answer 17

Nitrification
NH4+ + (O) -> NO2- + H2O - Nitrosomonas, Nitrosococcus
NO2- + (O) -> NO3- Nitrobacter, Nitrococcus

Denitrification
NO3 -> NO2 -> N2
- Dissimilatory nitrogenous oxide reduction
- Microaerophilic
- Bacillius licheniformis, Pseudomonas stutzeri, Thiobacillus denitrificans
- End product is gaseous N (N2, N2O)

Nitrogen fixation
- Diazotrophs
- Cyanobacteria e.g. Methylococcaceae
- N2 reduced to NH4 by nitrogenase
- Very O2 sensitive - anaerobic process
- Anaerobic fixation - Clostridium
- Aerobic fixation requires specific adaptations

Question 18

Nitrogen cycle

Answer 18

NH4 -> NO2 by Nitrosomomas
NO2 -> NO3 by Nitrobacter
NO3 -> N2
N2 -> NH4
NO2 -> N2
NO3 -> NH4 via organic N

Question 19

Guild G: Methanogenic bacteria

Answer 19

• Within Archaea, bacteria carry out methanogenesis
• CO2 + 4H2 -> CH4 + 2H2O
  CH3COOH -> CH4 + CO2 in acetate, methanol, methylamines
  Chemolithoautotrophs
  Obligate anaerobes
  Methanobacterium, Methanoplanus, Methanospirillum, Methanococcus

Question 20

How do methanotrophs utilize methane?

Answer 20

Methanotrophy - Use of CH4 as sole C source

CH4 – Methanol – Formaldehyde – Formate – CO2
Formate – accumulated in biomass

Aerobic/Microaerobic – O2 is the electron acceptor
CO2 is the electron acceptor for methanogens