Transcript Micro Lect-20 - ASAB-NUST

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LECTURE 20:
Microbial Growth In Natural
Environments; Biofilm and Quorum
Sensing
Microbiology and Virology; 3 Credit hours
Atta-ur-Rahman School of Applied Biosciences (ASAB)
National University of Sciences and Technology (NUST)
Biofilm Formation
Planktonic
Loosely Bound
EPS secreting
Biofilm Definition
• Biofilms are communities of microorganisms
in a matrix that joins them together onto
living or inert substrates
• Biofilms are surface attached communities of
bacteria, encased in an extracellular matrix of
secreted
– proteins,
– carbohydrates,
– and/or DNA,
Biofilm Formation
Biofilm Formation
Biofilm Formation
Biofilm Formation
Biofilm Formation Steps
• Biofilms can form on virtually any surface, once it
has been conditioned by proteins and other
molecules present in the environment
• Microbes reversibly attach to the conditioned
surface and eventually begin releasing
polysaccharides, proteins, and DNA
• As the biofilm thickens and matures, the
microbes reproduce and secrete additional
polymers
• The end result is a complex, dynamic community
of microorganisms.
Biofilm Formation
Microbial Interaction in Biofilm
• The microbes interact in a variety of ways.
• For instance, the waste products of one
microbe may be the energy source for another
microbe.
• Finally, the presence of DNA in the
extracellular slime can be taken up by
members of the biofilm community.
• Thus genes can be transferred from one cell
(or species) to another.
Antimicrobial compound and Biofilm
• In the biofilm, microbes are protected from numerous
harmful agents such as UV light, antibiotics, and other
antimicrobial agents.
• This is due in part to the extracellular matrix in which they
are embedded.
• The resistance of biofilm cells to antimicrobial agents has
serious consequences.
• When biofilms form on a medical device such as a hip
implant, they are difficult to kill and can cause serious
illness.
• Often the only way to treat patients in this situation is by
removing the implant.
• Another problem with biofilms is that cells are regularly
sloughed off.
Continous shedding of bacteria from
Biofilm
Quorum Sensing
Cell-Cell Communication Within
Microbial Populations
• Previously microbiologists used to think of
bacterial populations as collections of
individual cells growing and behaving
independently.
• But about 30 years ago, it was discovered that
the marine luminescent bacterium Vibrio
fischeri controls its ability to glow by
producing a small, diffusible substance called
auto-inducer (acyl homoserine lactone).
Euprymna scolopes (Hawaiian bobtail
squid)
Euprymna scolopes and Vibrio fischeri
• The bacteria are housed within epithelial cavities, of this light
organ, encouraged to produce light through bacteria regulated
quorum sensing and oxygen provided by the squid.
• The squid uses this light organ in counter illumination, a technique
that camouflages the squid within the environment.
• Since the squid is active at night, the light from the moon and stars
can penetrate the shallow water and illuminate the squid’s
presence to its prey or predators.
• Through sensors on the squid’s back, the squid is able to match the
amount of ambient light by manipulating the amount of light given
off by the light organ with its ink sac.
• Thus, the squid does not have a shadow. Every morning, the squid
expels about 90% of the bacteria from the light organ, allowing a
fresh culture for the remaining bacteria to flourish in as the squid
buries itself in the sand for the day.
G (-ve) Bacteria and SQ
• Pseudomonas aeruginosa use AHLs to regulate
the expression of virulence factors
• The plant pathogens Agrobacterium
tumefaciens will not infect a host plant and
Erwinia carotorvora will not produce
antibiotics without AHL signaling
G (+ve) Bacteria and SQ
• Gram positive bacteria usually exchange short peptides
called oligopeptides instead of autoinducer like
molecules.
• Enterococcus faecalis, whose oligopeptide signal is
used to determine the best time to conjugate (transfer
genes).
• Oligopeptide communication by Staphylococcus aureus
and Bacillus subtilis is used to trigger the uptake of
DNA from the environment.
• The soil microbe Streptomyces griseus produces a
gamma-butyrolactone known as A-factor.
• This small molecule regulates both morphological
differentiation and the production of the antibiotic
streptomycin.
Learn to be an
independent learner !!