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Note: we are switching the order of topics for Lectures 15 & 16. Bacterial Physiology (Micr430). Lecture 15 Bacterial Physiological Adaptation (Text Chapter: 18.1; 18.5; 18.7). GLOBAL CONTROL NETWORK.

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bacterial physiology micr430
Note: we are switching the order of

topics for Lectures 15 & 16

Bacterial Physiology (Micr430)

Lecture 15

Bacterial Physiological Adaptation

(Text Chapter: 18.1; 18.5; 18.7)

global control network
  • A cell must coordinate many different regulatory circuits that control many aspects of cellular physiology in response to changes in the environment - global control
  • Global regulatory networks include sets of operons and regulons scattered around chromosome
two component systems
Two-component systems
  • Bacteria sense and respond to changes in outside world primarily through a network of two-component signal transduction mechanisms
  • It consists of a sensor/kinase component (usually located on inner membrane) and a regulatory protein component (response regulators) located in the cytoplasm

Regulatory system

Fig. 18.1

two component systems1
Two-component systems
  • Histidine kinases (HKs) have two domains, an input domain (N-terminal) and a transmitter domain (C-termina)
  • HK receives a signal at its input domain and autophosphorylates at a histidine residue in its transmitter domain
  • HK then transfers the phosphoryl group to an aspartate residue in the receiving domain of the partner response regulator
two component systems2
Two-component systems
  • Response regulators (RRs) also have two domains, a receiver domain (N-terminal) and an output domain (C-terminal)
  • After obtaining a phosphoryl group from HK, RR is activated and transmits the signal to its target via its output domain
  • Most of known phosphorylated RRs bind to DNA and stimulate or repress transcription of specific genes
two component systems3
Two-component systems
  • The signaling pathway also includes a phosphatase that dephosphorylates the RRs, returning it to the nonstimulated state
  • The phosphatase may be the histidine kinase itself, the response regulator, or a separate protein
  • Additional proteins or enzymes may be needed for “two”-component systems that functions as carriers of phosphate – phosphotransferases
  • This phenomenon is phosphorelay
response to inorganic phosphate supply the pho regulon
Response to Inorganic Phosphate Supply: The Pho Regulon
  • Regulon is a set of noncontiguous operons or genes controlled by a common regulator
  • Bacteria have evolved a signaling system to induce the formation of phosphate assimilation pathways when the supply of phosphate becomes limiting
response to inorganic phosphate supply the pho regulon1
Response to Inorganic Phosphate Supply: The Pho Regulon
  • Under low phosphate conditions, E. coli stimulates transcription of at least 38 genes (most of them in operons) involved in phosphate assimilation
  • PhoR is HK; PhoB is RR
  • Pho regulon is controlled by PhoR via PhoB
  • Phosphorylated PhoB activates transcription of genes in the Pho regulon
pho signal transduction
Pho signal transduction
  • Components involved are:
    • PstS, a periplasmic Pi binding protein
    • PstA, PstB and PstC, integral membrane proteins required for Pi uptake
    • PhoU
    • PhoR, detects Pi, either directly or indirectly
    • PhoB
response to osmotic pressure and temperature
Response to Osmotic Pressure and Temperature
  • When E. coli is growing in higher osmolarity or at high temperature, the synthesis of the bacterium’s slightly smaller porin channel, OmpC, increases relative to the larger OmpF channel
  • Smaller OmpC channel is advantageous to the cell when faced with higher osmolarity pressure
response to osmotic pressure and temperature1
Response to Osmotic Pressure and Temperature
  • EnvZ is an inner membrane histidine kinase that is proposed to be an osmotic sensor
  • EnvZ is a transmembrane protein, with N-terminal end exposed to periplasm and C-terminal end exposed to cytoplasm
  • OmpR is the response regulator
Model for regulation

of porin synthesis

Fig. 18.12