This document discusses how bacteria sense and respond to surfaces. It describes different types of surface signals bacteria can detect, including osmolarity, chemicals, and mechanical signals. It also explains how bacteria use various structures and pathways to transduce these surface signals, such as extracellular appendages like flagella, transporters, sensor kinases, response regulators, and two-component signaling systems. While research has provided insights into these surface sensing mechanisms, key questions remain about how bacteria precisely detect mechanical forces and how signaling pathways interact and integrate multiple surface signals.

2. 1. Introduction
2. Surface sensing
3. Different types of signals
4. Sensors
5. Enveloped sensors
6. Signal transduction
7. Conclusion:

3. Unicellularity
of bacteria
• Multicellular communities in the presence of biotic
or abiotic surfaces
• Biofilms
• Swarming motility
• Both biofilm and swarming e.g E- coli, P. aeruginosa
Resistance to
adverse
conditions
• Resistance to antibiotics and metal
treatments
• High cell density protects Salmonella,
Bacillus, Serratia [Butler, 2010] and E. coli
[Perrin, unpublished data] against biocides
• Result is increased virulence [ James 2008 ]
Bioremedia-
tion
• Knowledge of the molecular basis of the behavior of
switch
• identification of the switch signals

4. Biofilm formation:
Free-floating bacterium collides with a surface
Biofilm development is the anchorage of the cell to a support (cellular or
abiotic)
Cascade of
physiological
reactions
Different species
and different
experimental
conditions
repression of motility
functions, production of
more adherence factors,
and production of
exopolysaccharides
[Beloin 2008 ]
Numerous highly
diverse
stimuli affect biofilm
formation
contact-dependent
signalling [Belango 2009]

5. Osmolarity
• differences in water
activity = allowing
bacteria to recognize a
solid-liquid interface
• sessile
bacteria=higher
concentration of
intracellular
potassium, compared
to the free-floating
cells.
• ion-sensitive field
effect transistor
(ISFET) [Possonet
2008 ]
• Curli-proficient
[Leugene 2003]
Chemicals
• metabolites (glucose,
indole, polyamines
etc)
• inorganic molecules
(iron, phosphate),
• quorum signals
• antimicrobials (host-
derived molecules
such as bile salt,
epinephrin and
norepinephrin,
antibiotics, metals,
detergents, H2O2
etc)[Karatan 2009]
Mechanical signals
respond to surface
contact
surface stiffness=
genetic
program=specific
pattern of adhesion and
cytoskeletal
Organization [Discher
2005]
Increase in substrate
stiffness=
Staph.epidermis and E-
coli [ Litcher 2008]

6. Signals Contd……
 P. aeruginosa responds to increasing surface stiffness (produced by raising the
concentrations of agar in solid media) by an increase in the production of type IV
pili.
 Surface attachment appears, then, to regulate not only the production but
also the polar localization of the pilus component. [Cowles 2010]
 Urinary tract-associated E. coli often produce adhesive type 1 pili exhibiting
the adhesin FimH at the tip.
 FimH binds to glycoproteins carrying high-mannose-type oligosaccharide
chains and, more generally, to mannose.
 A histidine tagged version of FimH has been created to enable transgenic E.
coli to attach to immobilized nickel.
 The transcriptional response to attachment was then compared in modified E.
coli cells (beads coated with nickel) and in parental cells (agarose beads coated
with mannose) suggesting that a mechanical signal is transmitted from the
outside to the intracellular structures, following fimbrial adhesion [Bhomkar
2010]

7. Extracellular appendages:
 Flagella = role in adherence to host cells, clumping, and biofilm formation
in many ways [Anderson 2010]
 act as adhesins
 cessation of flagellar motility and repression of flagellar gene transcription.
 a molecular clutch [Blair 2008]
 mutations in the flagellar motor : bacteria is immobilized on a surface =flagellar
motor stops, the ion flow through the motor ceases and the membrane
potential is transiently increased= signal for biofilm formation
Bacterial Flagellum
Basal body Hook Filament

8.  Swarming: coordinated translocation of a cell population across a solid or
semi-solid surface driven by type IV pili or flagella Proteus mirabilis and in
Vibrio parahemolyticus[Jarell 2008]
No data available on the use of the flagellum as a mechanosensor and one
pending question is how widespread this role might be?????
Sensing mechanism allowing the cell to distinguish a
“semi-solid surface” (swarming) from a solid surface (biofilm) is still obscure
[Wang 2012]

9. Transporters:
 efficient co-sensors e.g Fumarate sensing: signalling pathway involving
DcuS/DcuR, controlling the response to extracellular fumarate. [Kleefeld
2009]
 Outer membrane protein OmpA in E. coli, and its ortholog OprF in P.
aeruginosa, are both involved in biofilm formation, as well as having a variety
of other functions
 OmpA induces envelope stress Cpx signalling pathway [Ma Q 2009]
NlpE/Cpx pathway.
Via Cpx, Bae, Rcs, Psp and σE pathways
Chemical
stresses
Physico-
chemical
stresses
mechanical
stresses
response to various stresses applied the envelope
either by use protein phosphorylation in response to environmental
stimuli or sigma E regulated release or binding of a transcriptional
factor.

10. Scr pathway. In V. parahaemolyticus, the scrABC operon controls the switch between
swarming and biofilm formation via the inverse regulation of lateral flagella genes (laf) and
capsular polysaccharide genes (cps)
Focal adhesion. A focal adhesion is an anchoring junction of the cell to a substrate. In
eukaryotic cells, it links the internal actin-myosin network to the extracellular matrix
through transmembrane linkers, such as integrins.[Maureillo 2010]
Cytoplasmic sensors
H-NS. H-NS is a nucleoid-associated protein acting as a global regulator of gene expression,
and it is essential for bacterial virulence and environmental adaptation [Higgins 1988]
Frz pathway. The soil bacteria M. xanthus uses [Bao 2009]
Conclusion
• sensing obviously occurs at multiple levels, extracellular appendages, the envelope, and/or
cytoplasmic sensors
• surface-sensors are all proteins but the mechanisms of mechanical force sensing via
proteins are still obscure.
• molecular basis by which the flagellum communicates with the transcriptional machinery
is still poorly understood
• physical (temperature) or chemical (pH) parameters, protein deformation probably plays a
major role in response to mechanical forces.

11. Modularization of signalling pathways:
 On the basis of genome analysis, one-component systems appear to be more widely
distributed, and more abundant, in bacteria.
experiments investigating E. coli biofilm formation identified the transfer of phosphate
groups by two-component signal transduction systems as the main mechanism employed
to process environmental information [Nifa 2007]

12. Sensor kinase:
Korchid 2006

13. Response Regulator:
 Two domains constitute the RR, a highly conserved receiver domain (REC) and a
variable output or effector domain.
 Phosphorylation mediates dimerization of the receiver domains and activates
transcriptional function, or enzymatic activity in the case of diguanylate cyclase
catalytic domains [Gao 2010]
Auxiliary-regulators:
 Recently concept of co-sensors or auxiliary regulators modulating phosphotransfer
along the basic two-component signalling pathway has emerged.
 Auxiliary regulators are widespread, both in Gram-positive and Gram-negative
bacteria, and can be found either in the cytoplasm (for example E. coli PII protein as
the modulator of the NtrBC pathway in the nitrogen response) or in the inner
membrane (for example IgaA and MzrA) [Gerken 2010]

14.  Numerous regulatory devices ensuring signal transduction in
response to surface-sensing have been identified in bacteria but the
nature of the signal detected is still difficult to approach
experimentally.
 The role of extracellular appendages, such as flagella, in
surfacesensing and, more generally, mechanisms of
mechanotransduction need to be investigated.
 An exciting hypothesis is that large proteic assemblies, able to both
sense and regulate the response to a surface, may exist in bacteria.
Moreover, although huge progress has been made in the
characterization of individual regulatory pathways, we are just
beginning to address the complexity of the interactions between
the different elements.
 Evaluating the in vivo extent of the numerous possibilities of
crosstalk is a major challenge.