Transcript Wk2- QuorStreps

Biofilms
• Dense aggregates of
surface-adherant
microorganisms
embedded in an
exopolysaccharide
matrix.
• 65% of human
bacterial infections
involve biofilms!
Streptoccus spp.
• S. mutans – ubiquitous in oral microflora.
• Ecologic niche:
– Biofilms can lead to dental caries
– Acid tolerant response
– Natural genetic competence
– Bacteriocin activity
DENTAL CARIES – demineralization of
the tooth by bacteria.
http://www.db.od.mah.se/car/data/cariesser.html
Quorum sensing
• Cell-cell communication.
• Production, detection, and response to
autoinducers (extracellular signaling
molecules).
• Bacteria can monitor population density
and coordinate gene expression.
Quorum sensing
• Involved in regulation of biofilms,
virulence, antimicrobial production,
bioluminescence, etc.
• Gram positive and gram negative bacteria.
• Inter- and intra-specific communication!
Henke and Bassler, 2004. Three parallel quorum-sensing systems regulate gene expression in Vibrio harveyi.
Journal of Bacteriology 186: 6902-6914.
Biofilms
• Facilitate horizontal gene transfer?
– S. mutans biofilm transformation frequences
10-600 x that of planktonic cells.
– Subpopulations in biofilms constantly
competent for DNA uptake compared to 15-30
min. transient state in planktonic cells.
Dental biofilms
• Oral environment stressors:
– Nutrient shortage and excess
– Low pH
– High osmolarity
– Oxidation
– Host ingestion of antimicrobial agents.
Genetic transformation for antimicrobial
resistance or virulence factors may provide
important selective advantages to bacteria in
these environments.
Acid Tolerance Response
ATR experiments:
– Exposure to pH 5.0-6.0 allows the bacteria to adapt
and survive at 3.0-3.5.
– Filtrates from acid-adapted cells induced an ATR in
cells not exposed to low pH.
– Bacteria grown at high density adapted faster than
cells grown at low density.
– S. mutans biofilms more resistant to low pH and even
grew at the low pH after a glucose pulse in contrast to
planktonic cells.
Biofilm survival advantage
• High population density.
• High concentration of signal molecules.
• Heterogenous adaptation possible.
• Bacteria sensing stress can signal more
distant bacteria to adapt!
Mucosal pathogens
• Bacterial concentrations are often lower on
mucosal surfaces than in dental plaque
due to bathing effects of secretions and
desquamation.
• Quorum sensing still important:
– S. pneumoniae quorum sensing mutant was
less virulent than parent strain in mouse
model.
Bacteriocins
• Antimicrobial peptides generated by bacteria
that target other bacteria.
• Quorum sensing pathways involved:
– S. pyogenes has parts of quorum sensing
apparatus but not CSP to enhance DNA uptake.
– A specialized niche to regulate bacteriocin
activities in a cell density dependent manner to
outcompete other bacteria on mucosal surfaces,
but not involving DNA uptake? Other signals?
http://cgi.darwinawards.com/cgi/frames.pl?/book/3chapter05.html
-Squid-bacteria symbiosis involving quorum
sensing, trickery, and a daily love-hate relationship!
Symbiosis Strategy
The players:
• Euprymna scolopes – a Hawaiian squid
• Vibrio fischeri – bioluminescent bacteria
Timing is everything…
• At birth – squid light organ has no bacteria.
• Within hours – symbiotic colonization.
• Each morning – >90% of bacteria expelled from
squid light organ.
• Each night – bacteria multiply in squid light organ
and bioluminesce for squid camouflage.