Adaptive and Environmental Changes Flashcards
Responses by facultative Anaerobes to Anaerobiosis
-shift from aerobic to anaerobic atmosphere results in repression of genes required for aerobic growth and induction of genes required for anaerobic growth
Key Changes during shift from aerobic to anaerobic respiration
- final e’ acceptor is not oxygen (nitrate, fumarate, DMSO)
- alpha keto glutarate dehydrogenase synthesis is repressed
- replacement of fumarase A and succinate dehydrogenase by fumarase B and fumarate reductase
- acetyl-CoA is made by pyruvate lyase instead of pyruvate dehydrogenase
TCA under anaerobic conditions
- TCA becomes non-cyclic and reductive because alpha keto glutarate dehydrogenase is absent
- electron transport chain is altered and electrons flow to acceptors other than oxygen
4 systems in E.coli to bring about changes to anaerobic respiration
- The ARC (aerobic respiratory control)
- FNR (fumarate nitrate reductase)
- Nar (regulates expression of genes needed when nitrate and nitrite are electron acceptors)
- Formate regulon (fh1) (formate hydrogen lyase complex that converts formate to H2 and CO2)
The Arc System
- ArcA as the response regulator
- ArcB as the sensor
- induction of pyruvate formate lyase expression
The Arc System regulates the repression of… (5)
- cytochrome o and d oxidases
- TCA cycle enzymes
- Glyoxylate cycle enzymes
- several dehydrogenases for aerobic growth
- fatty acid oxidation
ArcB histidine kinase
- contains 3 phosphotransfer signaling domains
- suggested that ArcB senses the redox state of the cell or metabolites generated by anaerobic respiration
Fumurate Nitrate Reductase Regulation
- represses cyt o, cyt d and nar operon
- senses O via O sensitive (4Fe-4S) center
- exposure to O causes the disassembly of 2 (4Fe-4S) centers to from 2 (2Fe-2S) centers-cannot bind DNA and affect Tc
pH Stress and acid tolerance-Acid Tolerance Response
- exposure of bacteria to non lethal acidic pH results results in induction of genes that protect the cell from lethal pH conditions
- acid shock proteins
Mechanisms of ATR
- Production of glutamate decarboxylase-export gamma-amino butyric acid, import more glutamate
- Production of arginine deiminase-coverts arginine to ammonia, citrulline. citrulline converted to ammonia and Co2, ammonia can alkalize the environment
- production of urease-converts urea to ammonia and Co2
Heat shock response
- when bacteria shift to higher temp. they respond by increasing the synthesis of heat shock proteins
- classified into families according to molecular weight
- similar across phylogenetic lines
Sigma Factor 32 (RpoH)
- increase in Hsp synthesis due to increased stability and TL of sigma factor 32
- temp upshift melts secondary structures in 5’ region of rpoH mRNA-increased TL of rpoH
- temp upshift also increases stability of sigma32 protein
- at 30 degrees sigma 32 is bound by chaperones and easily degraded by proteases
- at 42 degrees bound by RNA pol and protected from proteases
Response to envelope stress
-arises from accumulation of misfolded proteins in the periplasm
2 response pathways:
-extracytoplasmic function (ECF) sigma factor
-CpxRA 2 component system
Regulation of ECF sigma factor
When stress is absent
- RseA bound by RseB from periplasm
- C-terminus of RseA binds sigma factor E sequestering it from RNA pol
- RseA is anti sigma factor
Under stress
- RseB binds misfolded proteins in periplasm
- RseA is degraded by proteases
- sigma factor E is released, initiates Tc
Regulation by CpxRA
- responds to envelope stress by autophos followed by phosphotransfer to CpxR
- CpxR-P activates expression of enzymes needed to refold misfolded proteins
- activates periplasmic protease DegP using sigma factor E
