Halomonas sp. GFAJ-1

Question 1

What were the issues with the media?

Answer 1

The -P/+As still had enough P from contamination to grow
The -P/-As media had no vitamins or carbon source

Question 2

How did they figure out how many cells could grow from the 3 microM PO4 contamination?

Answer 2

(3x10^-6 mol/L PO4)(31 g/L) = 9.3x10^-5 g of P/L

Each dry cell is 1% P so 1% of (9.3x10^-5 g of P/L) = 9.3x10^-3 g dry weight/L

Each dry cell weighs 3x10^-13 g/cell so (9.3x10^-3 g dry weight/L) / (3x10^-13 g dry weight/cell) = 3.1x10^10 cells/L = 3.1x10^7 cells/mL

This is what they got experimentally proving their growth was due to PO4 contamination

Question 3

Why is arsenate (AsO4^3-) toxic?

Answer 3

If incorporated into biomolecules they no longer function properly. Example, arsenate esters in DNA hydrolyze almost instantly causing DNA breaks

Question 4

What are the 2 ways phosphate is taken up?

Answer 4

Low affinity, low selectivity H+ symporter (Pit)
High affinity, high selectivity ABC transport system (Pst)

Question 5

The genome predicts GAFJ-1 to have which transport systems?

Answer 5

It has 2 Phosphate Specific Transport (Pst)-like ABC transporter systems which have high affinity and high selectivity for phosphate.

Each has their own periplasmic binding protein (PBP-1 and PBP-2)

Question 6

The largest family of energy driven transport systems is what?

Answer 6

ATP-Binding Cassette superfamily of transporters (ABC transporters)

Question 7

What are the 3 components of an ABC transporter?

Answer 7

Periplasmic binding protein - provides specificity and affinity
Transporter - transmembrane channel
ATP-binding protein - provides energy

Question 8

Which PBP is more selective for phosphate?

Answer 8

PBP-2 is selective for phosphate over arsenate by over 4500 fold