Lecture 11 - microbial nutrition

Question 1

What are essential nutrients?

Answer 1

Nutrients that must be supplied from the environment

Question 2

Bacterial macronutrients

Answer 2

Major elements in macromolecules: CHONPS
Metal ions for nucleic acid/protein structure and function: Mg, Ca, Fe, K

Question 3

What is Mg used for in the cell

Answer 3

Nucleic acid structure and stability

Question 4

Why can iron be limiting to bacterial growth?

Answer 4

Bacteria take iron from the environment for electron transfer

Question 5

Micronutrients for bacteria

Answer 5

Trace elements necessary for enzyme function: Co, Cu, Mn, Zn

Question 6

Autotroph

Answer 6

Can assimilate inorganic carbon into organic carbohyrates

Question 7

Heterotroph

Answer 7

Assimilates preformed organic carbon-containing molecules

Question 8

Why do some bacteria require additional growth factors?

Answer 8

Evolved away from production of all necessary molecules.
- pathogenic species have evolved to depend on the host for certain materials

Question 9

Minimal medium

Answer 9

Contains only compounds needed for an organism to grow

Question 10

Prototrophs

Answer 10

Can synthesize complex compounds from simpler organic molecules (ex: wild type E. coli can make all of its amino acids from glucose)

Question 11

Auxotrophs

Answer 11

Must obtain biologically important molecules in a pre-formed state from the environment or from hosts
- bacteria are usually referred to as auxotrophic for a particular substance that they need

Question 12

Do bacterial nutrients generally cross the membrane?

Answer 12

No, normally hydrophilic or charged
- ammonia is an exception

Question 13

How do nutrients get into the cell?

Answer 13

Permeases: substrate-specific carrier proteins

Question 14

How does LacY (lactose permease) transport lactose into the cell?

Answer 14

Secondary active transport using proton gradient

Question 15

Group translocation

Answer 15

Process that uses energy to chemically alter a substrate during transport

Question 16

Example of group translocation in bacteria

Answer 16

Phosphotransferase system (PTS)

Question 17

How does the phosphotransferase system work?

Answer 17

Uses energy from phosphoenolpyruvate (PEP) to phosphorylate specific sugars during transport.
- can be hooked up to different carbohydrate importers

Question 18

Why are sugars phosphorylated on import?

Answer 18

Phosphorylated sugars are different than non-phosphorylated sugars. Keeps the concentration gradient tending towards import of sugars.

Question 19

Catabolite repression between glucose and lactose

Answer 19

E. coli will preferentially use glucose until consumed. Then it will switch to lactose metabolism.

Question 20

Mechanism of catabolite repression between glucose and lactose

Answer 20

Glucose shuts down expression of the lacZ gene
- if lots of glucose is moving through the transporter, it is phosphorylated at such a high rate that parts of the LacY system can’t be phosphorylated
- LacY stops import of lactose
- decreased import of lactose –> repression of lac operon expression

Question 21

What do ABC transporters typically move?

Answer 21

• Import of carbohydrates and AAs
• export of small molecules like hemolysin or cytotoxic materials

Question 22

Where are ABC transporters located?

Answer 22

Inner membrane

Question 23

How do Gram negative bacteria import materials?

Answer 23

• Outer membrane transporters bring material into periplasmic space
• periplasmic binding proteins shuttle material to the ABC transporter
• ABC transporter brings material into cell

Question 24

Siderophores

Answer 24

Secreted molecules that bind ferric ions (Fe 3+) for transport into the cell

Question 25

General structure of siderophores

Answer 25

Flat molecules that fold up into a cage to encapsulate charged iron

Question 26

Mechanism of siderophore uptake into the cell

Answer 26

Active transport by TonB-ExbB-ExbD system
- EbB and D perform a mechanical up/down motion thru ATP hydrolysis that is relayed to TonB
- TonB displaces a plug in an outer membrane transporter that allows siderophore into periplasmic space

Question 27

Iron piracy

Answer 27

Some cells will make transporters for particular siderophores without actually making the siderophore –> can steal packaged iron from other bacteria

Question 28

Hemin

Answer 28

Molecule that sequesters iron
- analogous structure to siderophores
- can be broken down by hemolysin from bacteria

Question 29

Hemin uptake in Gram + bacteria

Answer 29

Iron-bound hemin is passed between Isd molecules through the cell wall to the membrane where it can be transported inside

Question 30

What the issue with energy sourcing for outer membrane transport?

Answer 30

The periplasm does not contain ATP because it would be subject to loss to the environment. There must be another way to get energy