Microbial Ecology Exam 2
Quorum sensing can be divided into at least 4 steps
(1) production of small biochemical signal molecules by the bacterial cell (2) release of the signal molecules, either actively or passively, into the surrounding environment (3) recognition of the signal molecules by specific receptors once they exceed a threshold concentration, leading to (4) changes in gene regulation
3 well described systems for QS
-AI-1 system Acyl-homoserine lactones (AHLs) -Peptide -based Autoinducer peptides (AIPs) -AI-2 system Autoinducer-2 (AI-2)
AI-2 controlled processes:
-Induces mini cell formation -Induces expression of stationary phase genes -Inhibition of initiation of DNA replication
OCCURRENCE
-Within a single bacterial species as well as between diverse species -Some insects use quorum sensing to determine where to nest.
Microbial environments are?
-complex, constantly changing -expose a microorganism to overlapping gradients of nutrients and environmental factors -contain both micro and macroorganisms
Microbes have evolved many responses to starvation and environmental stress:
-morphological changes (endospore formation) -enter stationary phase of growth curve -use cellular components as nutrients -numerous genes and proteins that help -viable but not culturable state
How are bacteria beneficial passengers?
-they close up the ecological space in our bodies to keep out invading pathogens -some species can break down our food in ways we cant -they can synthesize certain vitamins that we cant
Bacteria showing quorum sensing requires two things -
1) Signalling molecules called autoinducers or pheromones 2)A receptor that can specifically detect the signalling molecule.
peptide- based system is how many parts and composed of what?
3 part system composed of gene cluster, an enzyme and two-component response system
•Born without TLR5, mice got 20% fatter than normal. The mice also had high levels of triglyceride, cholesterol, and blood pressure, even diabetes, why?
Because they ate more! The new community of microbes were making them hungry! If their diet was restricted to that of normal mice, they stopped eating as much and their health got better. But when they put this (bad) set of microbes into normal mice, the normal mice ate more and became unhealthy
It iscompact mass of differentiated microbial cells, enclosed in a matrix of polysaccharides. Biofilm resident bacteria are antibiotic resistant. Quorum sensing is responsible for development of thick layered biofilm.
Biofilm formation
It occurs in various marine bacteria such as Vibrio harveyi and Vibrio fischeri. Takes place at high cell density.
Bioluminescence
It is ability to take up exogenous DNA QS Increase competence in Bacillus subtilis
Competence
What protects microbes from harmful agents?
EPS and change in attached organisms physiology
AI-2 System have what kind of diester
Furanosyl borate
AI-2 System gram:
Gram negative and gram positive bacteria
Quorum
It means the number of members of a group required to be present to transact business or carry out an activity legally
how are biofilms formed
Microbes reversibly attach to conditioned surface and release polysaccharides, proteins, and DNA to form the extracellular polymeric substance (EPS)
is an autoinducer molecule produced by many Gram-negative organisms.
N-acylhomoserine lactone (AHL)
Virulence gene expression
QS up-regulates virulence gene expression
luxR binds to DNA and recruits:
RNA polymerase
QS upregulates spore-forming genes in Bacillus subtilis
Sporulation
Mice were engineered so that they didn't produce a protein normally found on the surface of gut cells, called
TLR5
what can recognize bacteria, and some studies suggest that the cells can then pass along signals to the immune system, possibly sending a stand-down command so that the immune system doesn't start trying to kill the microbes.
TLR5
So... what if these bacteria used QS to trigger production of a protein that disrupts TLR5
The bacteria would benefit because we would eat more, but we certainly don't benefit because we get obese and have heart disease and diabetes
Quorum Sensing
The process by which bacteria coordinate their behaviors in a density-dependent manner, using signaling molecules
what protozoan needs to get from rats to cats, and to help the process along, it makes rats lose their fear of cats and in fact be attracted to feline urine.
Toxoplasma
•Every time we take a dose of antibiotics, for example, the balance can change dramatically. And as the diversity of microbes changes, so do its ecological functions. (T/F)
True
Each bacterium continuously secreties a small molecule called _________ that can diffuse readily through the cell membrane.
VAI (Vibrio fischeri autoinducer)
One of the most widely studied bacteria is
Vibrio fischeri
Symbiosis
Vibrio fischeri and bioluminescence in squid
When the inducer binds the receptor , it _______ _________ of certain genes, including those for inducer synthesis.
activates transcription
AI-1 System have ____ homoserine lactone
acylated
What are produced as microbes reproduce and biofilm matures?
additional polymers
do interactions occur on attached or free floating organisms?
attached: exchanges take place metabolically, DNA uptake and communication
In this process bacteria communicate via secreted signalling molecules called __________ which contribute to the regulation of the expression of particular genes.
autoinducers
_______ are the most numerous of the light emitting life forms.
bacteria
quorum sensing
bacterial cells in biofilms communicate in a density-dependent manner
attached microbes (sessile) are members of a slime enclosed community called a
biofilm
what can be formed on any conditioned surface
biofilm
what are ubiquitous in water
biofilms
Discovery of QS example
bobtail squid
How are Acyl-homoserine lactones (AHLs) synthesized
by an autoinducer synthase LuxI and recognized by a autoinducer receptor/DNA binding transcriptional activator protein LuxR.
each morning the squid flushes out most of its _____ of glowing vibrios leaving enough cells to start the cycle anew.
cache
autoinducer peptides regulate?
competence and sporulating gene expressions
produce small proteins that increase in level as microbes replicate and convert a microbe to a ________ state.
competent
mature biofilm
complex, dynamic community of microorganisms
•When these autoinducers reach a _____ ________ ________, they activate bacterial quorum sensing genes that enable the bacteria to behave as a multicellular population rather than as individual single-celled organisms. In this way, individual bacteria within a group are able to benefit from the activity of the entire group.
critical threshold level
Thus, there is a _________ concentration of the small molecule in a growing circumference around the bacterium.
declining
heterogeneity
differences in metabolic activity and locations of microbes
So if TLR5 is present, immune system
doesn't kill those recognized by TLR5
oligotrophic
environment in which there are extremely low levels of nutrients
how do Acyl-homoserine lactones (AHLs) mediate communication
exclusively intracellular
planktonic
free floating microbes
When the local concentration of VAI is very ______, it binds to luxR, enabling it to bind to the operator (luxO) and turn on transcription
high
When there are many bacteria around, the local concentration of the small molecule will be very:
high
Processes regulated by quorum sensing involve
host-microbe interactions.
when biofilm microorganisms are formed on medical devices such as implants, what happens?
illness can result
If TLR5 is absent
immune system may kill (any, some, all, just different) bacteria
When the density of bacteria is very high, the bacteria know that they must be
inside a light organ instead of floating around in the ocean.
AI-2 System have what kind of communication
interspecies
AI-1 System _________ communication
intraspecies
ComX
involved in competence development
some microbes live in nutrient-______ environments
labile
If VAI is ______, luxR is in a conformation such that it cannot bind to the operator, and not very much luciferase can be made
low
LuxR is consistently transcribed at a _____ ______ so that there is always some around to affect regulation
low level
This increases transcription of the DNA and makes more
luciferase
The genes for making luciferase are contained in the:
lux operon
_____ is the gene that encodes for the enzyme that synthesizes VAI.
luxI
A DNA binding site:
luxO
Lux promoter
luxP
A DNA binding site (luxO) near the lux promoter (luxP) binds a protein called:
luxR
autoinducer peptides are recognized by?
membrane bound histidine kinase receptor
what cooperate with one another to get food they need and produce the conditions in which they can thrive (biofilm)
microbes
sessile
microbes grow attached to surfaces
AI-1 System are gram
negative bacteria
Most microbes inhabit what kind of environments?
oligotrophic
what can contaminate water phase above biofilm such as in a drinking water system
organism sloughing
The core of bacteria are found where in the human body
our gut
The water circulating through a hollow chamber in the squids body contains millions of species of microbes, but cilia in the squids light organ expel all but the V. fischeri cells. Once this is fed with _____ and _____ ______, they multiply and begin to emit light.
oxygen and amino acids
Peptide-based systems are gram:
positive bacteria
Pathogenicity and increased virulence factor
production
Acyl-homoserine lactones (AHLs) mediate ______ ______ in gram negative bacteria
quorum sensing
autoinducer peptides regulate what? in gram what?
regulate gene expression in Gram-positive bacteria such as Bacillus subtilis, Staphylococcus aureuas etc.
Why do bobtail squid get rid of their bacteria every day?
so the bacteria can change their environment to suit them rather than the host: bobtail squid.
CSF (competence and sporulation factor): regulates
spore formation
competence
the ability of a cell to alter its genetics by taking up extracellular DNA from its environment in the process called transformation
When a bacterium undergoes the transition from not making luciferase to making luciferase, it needs to have:
the autoinducer around in order to promote binding of LuxR to the operator
Bioluminescence is defined as
the emission of visible light from living organisms.
Scientists have found that if they transfer microbes from an obese mouse to a regular mouse that has had all its own germs stripped out, the recipient mouse will develop extra fat. In the case of these obese mice, it appears that:
the microbes become less efficient at helping the animals digest food, triggering a series of changes that leads the mice to be fat.
the bacteria only make luciferase when:
there are lots of other bacteria around
Once a certain population is reached, the bacteria can change their environment to suit what circumstances?
to suit them rather than their host.
Thus, luxR is a
transcriptional activator of the lux operon
Bobtail squids possess a "light organ" that shines with a blue glow, perfectly matching the amount of light shining down through the water (T/F)
true
The secret of the squids ability to stimulate moonlight is densely packed community of luminescent bacteria called?
vibrio fischeri
Do the diversity of microbes vary from person to person and change over our lifetime??
yes
are Acyl-homoserine lactones (AHLs) able to diffuse through the membrane
yes
Do we carry enough bacteria that outnumber our own cells?
yes, 10 trillion
N-acylhomoserine lactone (AHL)
•Diffuses across plasma membrane. Once inside the cell, induces expression of target genes regulating a variety of functions
What has debunked the idea that bacteria live solitary lives?
•that bacteria communicate using molecules comparable to pheromones. By tapping into this cell-to-cell network, microbes are able to collectively track changes in their environment, conspire with their own species, build mutually beneficial alliances with other types of bacteria, gain advantages over competitors, and communicate with their hosts - the sort of collective strategizing typically ascribed to bees, ants, and people, not to bacteria.
