Arsenite Oxidation in the Chemolithoautotroph NT-26

Question 1

Describe Rhizobidium NT-26

Answer 1

Isolated from a gold mine in Australia (Santini et al 2000)
Fastest arsenite oxidiser known so far
Able to grow on 5 mM arsenite without any other energy source (doubling time 7.6 h)
Gram-negative
2 flagella

Question 2

Describe Arsenite metabolism.

Answer 2

The AroA, AroB and Cyt C complex oxidises arsenite from A3- to A5-. This releases Xe-, which then acts upon both ATP synthase complex and BC1 complex, leading to the generation of ATP, H20, H+ gradient and NADPH.

Question 3

Describe gene organisation

Answer 3

aroS –> aroR –> aroB –> aroA –> cytC –> moeA

Question 4

What is aroS?

Answer 4

Histidine Kinase - His273 is required for

autophosphorylation

Question 5

What is aroR?

Answer 5

Response Regulator

Question 6

What have mutational studies of aroS and aroR shown?

Answer 6

Expression of both aroR and aroS is necessary
for arsenite oxidation. Expression of both aroS and aroR is constitutive. aroS/aroR genes are on a separate transcriptional unit to aroB – an arsenite inducible gene.

Question 7

What is DctB?

Answer 7

HK involved in C4-tricarboxylate transport and

metabolism. Ligand binding domain distal to aroS.