1. Environmental conditions?
Nutrients…
Oxygen…
Temperature… …. ? ? ? ? ? ? ? ? ?

2. Two-component regulatory systems Include:
1- a histidine kinase (HK), or sensory kinase. Receives a signal and phosphorylates a histidine residue
HK + ATP KH-P + ADP
2- a response regulator (RR). The RR is phosphorylated on an aspartate residue by HK-P
RR + HK-P RR-P (active) + HK
3- a phosphatase, that can be the HK, the RR or another protein
RR-P + H2O RR + Pi

5. MODEL OF HK ACTIVATION

7. OSMOREGULATION

8. Response to changes in osmolarity

9. PHOSPHATE AVAILABILITY

10. The PHO regulon

11. SENSING OXYGEN AVAILABILITY
The Arc system (aerobic respiration control)
Arc is responsible for:
1 – Repression, under anaerobiosis conditions, of genes encoding:
TCA enzymes
Glioxylate cycle enzymes
Several dehydrogenases necessary for growth under aerobiosis (piruvate dehydrogenase)
Enzymes involved in fatty acid oxidation
Citochrome o oxidase
2 – Induction, under anaerobiosis, of genes encoding:
Pyruvate formate lyase
3 – Induction, under low O2 concentrations, of gene encoding:
Citochrome d oxidase, cobalamine and pyruvate formate lyase

12. The Arc system (aerobic respiration control)

13. Responses to changes in oxygen availabitiy
The Fnr, SoxR, and ArcB
are involved in oxygen sensing
and regulation of metabolism
Shift aerobic/anaerobic

14. A schematic representation of signal transduction by the Arc two-component system.
Kwon O et al. J. Biol. Chem. 2003;278:
©2003 by American Society for Biochemistry and Molecular Biology

15. The FNR protein

16. The NarQ/NarP and NarX/NarL TCS are also involved in
anerobic/anaerobic transitions

18. Oxidative stress response in E. coli

19. The heat shock response

20. HSP are chaperones or proteases